Nanoparticles and the environment
ENVIRONMENTAL FATE AND ECOTOXICITY 2304 OF ENGINEERED NANOPARTICLES 2007
Nanoparticles and the environment (TA-2304/2007)
This report may be cited as: Norwegian Pollution Control Authority (2008) Environmental fate and ecotoxicity of engineered nanoparticles. Report no. TA 2304/2007. Eds.: E.J. Joner, T. Hartnik and C.E. Amundsen. Bioforsk, Ås. 64 pp.
ISBN 978-82-7655-540-0
2 Nanoparticles and the environment (TA-2304/2007)
Environmental fate and ecotoxicity of engineered nanoparticles
Norwegian Pollution Control Authority Report no. TA-2304/2007
This report has been produced by Bioforsk (Norwegian Institute for Agricultural and Environmental research) on behalf of the Norwegian Pollution Control Authority (Statens forurensningstilsyn).
Authors: Erik J. Joner, Thomas Hartnik and Carl Einar Amundsen
Project leader: Erik J. Joner, Bioforsk Soil and Environment.
Responsible at the Pollution Control Authority: Bård Nordbø
3 Nanoparticles and the environment (TA-2304/2007)
Preface
The present report is a review of scientific results on the potential negative impact of engineered nanoparticles on the environment. It is intended as a background document for the Norwegian Pollution Control Authority (Statens forurensningstilsyn) in their work with regulatory issues related to the release of engineered nanoparticles into the environment. The report was written by senior scientist Erik J Joner and colleagues at the Soil and Environment Division of BIOFORSK (Norwegian Institute for Agricultural and Environmental Research), who are currently conducting research in this area. Responsible at the Norwegian Pollution Control Authority has been Bård Nordbø.
Forord
Denne rapporten er en gjennomgang av vitenskaplig litteratur som omhandler mulige negative miljøvirkninger av produserte nanopartikler. Den er ment som et bidrag i Statens Forurensningstilsyns arbeid med forvaltningsmessige problemstillinger i forhold til utslipp og spredning av produserte nanopartikler til miljøet. Rapporten er skrevet av seniorforsker Erik J Joner og medarbeidere ved Bioforsk Jord og Miljø som deltar aktivt i forskning på dette området. Kontaktperson i Statens forurensningstilsyn har vært Bård Nordbø.
Ås, January 2008
Erik J Joner Senior scientist, Bioforsk Soil and Environment
4 Nanoparticles and the environment (TA-2304/2007)
Table of contents
1. Summary...... 6. 2. Norsk sammendrag (Norwegian summary) ...... 7. 3. Abbreviations ...... 8. 4. Background ...... 9. 5. Definitions ...... 11. 6. Crude classification and occurrence of nanoparticles ...... 13. 7. An overview of different types of engineered nanoparticles (ENPs)...... 15. 8. How to describe nanoparticles ...... 19. 9. Methods to describe and detect nanoparticles ...... 22. 9.1. Qualitative methods ...... 22. 9.2. Quantitative methods for measurements in environmental samples ...... 23. 10. State-of the-art knowledge on behavior and ecotoxicity of ENPs ...... 26. 10.1. Background ...... 26. 10.2. Mobility of ENPs ...... 27. 10.3. Other aspects affecting the fate of ENPs ...... 29. 10.4. Degradability ...... 29. 10.5. Toxicity and ecotoxicity, general considerations ...... 30. 10.6. Reactive oxygen species (ROS) ...... 31. 10.7. Ecotoxicity ...... 32. 10.8. Bioassays – taking bioavailability into account ...... 33. 10.9. Ecotoxicity of C60 fullerenes...... 34. 10.10. Ecotoxicity of carbon nanotubes ...... 36. 10.11. Ecotoxicity of metal nanoparticles ...... 37. 10.12. Ecotoxicity of oxide nanoparticles ...... 38. 10.13. Ecotoxicity of other nanoparticles ...... 39. 11. Exposure to ENPs ...... 40. 12. Environmental hazards and risks...... 42. 12.1. Background ...... 42. 12.2. Environmental risk assessment of nanoparticles ...... 43. 12.2.1. Overview ...... 43. 12.2.2. Hazard assessment ...... 43. 12.2.3. Dose-response assessment ...... 43. 12.2.4. Exposure assessment ...... 44. 12.2.5. Risk characterisation ...... 46. 12.3. Current state of environmental risk assessment of ENPs ...... 46. 12.4. Challenges in the risk assessment of ENPs ...... 48. 12.5. The European Commission’s efforts on risk assessment of ENPs ...... 49. 12.6. Norwegian efforts in risk assessment of ENPs ...... 50. 13. Regulatory efforts ...... 51. 14. Future research needs ...... 53. 15. Further reading ...... 55. 16. References ...... 57.
5 Nanoparticles and the environment (TA-2304/2007)
1. Summary
The present report is an overview of the scientific knowledge on potential negative effects that engineered nanoparticles may have on the environment. Research and development in nanotechnologies increase strongly and attract substantial funding, but environmental consequences of resulting materials and applications are poorly known. One group of nanomaterials, namely free engineered nanoparticles, have attracted attention in this context, as they have been highlighted as a group of materials that may have potentially adverse effects on human health and the environment. Research on human and environmental toxicity (i.e. ecotoxicity) of this group of materials has recently started, and draws upon existing knowledge in toxicology, ecotoxicology and environmental sciences in an attempt to predict potential future problems related to spreading of engineered nanoparticles in the environment.
This report has gathered the existing knowledge in this area as an aid to Norwegian regulatory bodies to take proactive initiatives to prevent future large-scale environmental problems with these materials. Such efforts will also depend on coordinated international initiatives in which Norway wish to play an active part.
The report points out that a number of engineered nanoparticles are indeed suspicious in an environmental and ecotoxicological context. Yet, no immediate action seems necessary to prevent pollution with these particles in Norway since there are no current applications that are expected to result in significant losses to the environment.
Regulatory initiatives should be based on demonstrated or suspected harmful effects of specific nanoparticles and a high probability of such particles being mobile in the environment. So far, scientific evidence show that some nanoparticles have toxic effects under laboratory conditions, but practically nothing is known about their mobility and uptake in organisms under environmental conditions. There is thus an urgent need for research on interactions between nanoparticles and environmental matrices (water, sediments and soils) and ecotoxicity studies that take into account the anticipated modifying effect of such matrices on uptake in organisms and toxicity.
This report has been written by a group of researchers at Bioforsk Soil and Environment who are currently conducting research on environmental fate and toxicity of nanoparticles (Erik J. Joner), ecotoxicity studies (Thomas Hartnik) and environmental risk assessment (Carl-Einar Amundsen).
6 Nanoparticles and the environment (TA-2304/2007)
2. Norsk sammendrag
Denne rapporten gir en oversikt over hva som er kjent om mulige negative miljøeffekter av produserte nanopartikler. Forskning og utvikling innen nanoteknologi er et sterkt vekstområde som tilgodeses med store pengebeløp. Samtidig er miljømessige konsekvenser ved spredning og utslipp av nanomaterialer ukjent. En gruppe nanomaterialer, såkalte frie, produserte nanopartikler, har kommet i søkelyset i denne sammenheng idet man har påvist at denne typen nanomaterialer kan ha negative helse- og miljøeffekter. Forskning på disse materialenes giftighet og miljøgiftighet (dvs. økotoksikologiske effekter) har nylig blitt igangsatt, og trekker på kunnskap innen toksikologi, økotoksikologi og miljøfag i et forsøk på å beskrive mulige framtidige problemer som kan oppstå ved spredning av nanopartikler til miljøet.
Denne rapporten har samlet forskningsresultater på dette området som et hjelpemiddel for norske myndigheter til å ta et tidlig initiativ for å hindre at det skal oppstå betydelige framtidige miljøproblemer som skyldes spredning nanomaterialer. Om slike tiltak blir aktuelle vil de være avhengige av å samkjøres med tilsvarende internasjonale initiativer som Norge ønsker å tilslutte seg og være en aktiv del av.
Rapporten framhever at flere typer produserte nanopartikler er suspekte i forhold til økotoksisitet og spredning til miljøet. Likevel er det tilsynelatende ikke nødvendig med noen umiddelbare tiltak for å hindre forurensning med slike nanopartikler i Norge pga. at de har liten eller ingen anvendelse i som tilsier umiddelbare utslipp til miljøet.
Innføring av tiltak som angår bestemte typer nanopartikler må baseres på kjente eller antatte miljøskadelige egenskaper og en betydelig sannsynlighet for at slike partikler vil være mobile i miljøet. Så langt har forskning vist at noen typer nanopartikler har giftvirkning i laboratorieforsøk. Men svært lite er kjent om nanopartiklers mobilitet og opptak i organismer i jord vann og sedimenter. Det er derfor et presserende behov for forskning på interaksjoner mellom nanopartikler og slike miljøbestanddeler så vel som økotoksikologiske studier som tar hensyn til antatte endringer som slike miljøbestanddeler har på opptak i organismer og giftighet.
Denne rapporten er utarbeidet av en gruppe forskere ved Bioforsk Jord og Miljø. Deres faglige kompetanse er særlig knyttet til nanopartiklers toksisitet og mobilitet i miljøet (Erik Joner), økotoksikologi (Thomas Hartnik) og miljørisikovurderinger (Carl-Einar Amundsen).
7 Nanoparticles and the environment (TA-2304/2007)
3. Abbreviations
AFM Atomic force microscopy APS Average particle size BET (i.e. Brunauer, Emmett, Teller) Method for measuring surface area
C60 A fullerene consisting of 60 C atoms CB Carbon black, inorganic C. A major constituent of soot CNT Carbon nanotube EC50 Effective concentration reducing activity or survival by 50% ENP Engineered nanoparticle ERA Ecological risk assessment ICP-MS Inductively coupled plasma-mass spectrometry MWCNT Multi-walled carbon nanotube NA Neutron activation
nC60 Fullerene aggregate with enhanced water solubility NOEC No observed effect concentration NP Nanoparticle PEC Predicted environmental concentration PNEC Predicted no effect concentration Q-dot Quantum dot, a nanosized binary crystal for fluorescent imaging QSAR Quantitative structure-activity relationships RA Risk assessment ROS Reactive oxygen species SEM Scanning electron microscopy SWCNT Single-walled carbon nanotube TEM Transmission electron microscopy
8 Nanoparticles and the environment (TA-2304/2007)
4. Background
This section describes why this report has been written, in which way nanotechnology concerns us, and why the topic of spreading nanoparticles to the environment is causing concern. Today, we lack information both on which types of nanoparticles that may be harmful, and on production volumes and use of nanomaterials in general. Such information is necessary to determine if certain types of nanoparticles should be
considered as potentially harmful environmental pollutants.
The background for the present report is that the Norwegian environmental regulatory authorities need an Q: Why do you updated overview of the possible impacts that distinguish between nanotechnology and its derived materials may have on “nanomaterials” and the environment. Nanotechnology is still in its infancy, “nanoparticles”? so it is timely to consider the potential future problems A: Engineered before large amounts of materials/products reach the nanoparticles are the only market, and inevitably the environment. In this way, one nanomaterials that are may prevent undesirable large scale effects through likely to spread in the environment and be taken proactive approaches. Similar concerns all over the up by Man and other world have resulted in several panel investigations and a organisms. range of white papers or similar documents emerging from large countries and organizations (AFSSET 2006; Breggin and Pendergrass 2007; The International Risk Governance Council 2006; The Royal Society and the Royal Academy of Engineering 2004; UNEP 2007; US-EPA 2007). Similar efforts have taken place in our neighbor countries in Scandinavia (Kemikalieinspektionen 2007; Miljøstyrelsen 2007). The latter countries have traditionally set some of the world’s highest standards for protection of public health and the environment and are particularly relevant for comparisons with Norwegian activities. While the documents above all underline the lack of data for judging potential negative effects, they also illustrate the general concern and a will to investigate and prevent unforeseen risks.
Nanotechnology is an area where research and development are growing fast and attract substantial funding, both from public and private sectors. According to Lux Research, a New York-based independent intelligence and technology research and advisory firm (www.luxresearchinc.com), investments in the nanotechnology industry grew from $13 billion in 2004 to $50 billion in 2006. The firm projects that investments will reach $2.6 trillion by 2014. Consequently, large amounts of materials and products will be marketed and may come in contact with the environment, either during production, transport, use or when they end up as waste.
9 Nanoparticles and the environment (TA-2304/2007)
Nanotechnology is, however, not a single thing. It is rather a collective term that implies the capacity to work with materials (surface structures, pores, particles, etc.) at a nanometer scale. Nanotechnology thus has potential applications in a wide range of sectors, from energy (production, catalysis, storage), materials (lubricants, abrasives, paints, tires, sportsware), electronics (chips, screens), optics, remediation (pollution absorption, water filtering, disinfection), to food (additives, packaging), cosmetics (skin lotions and sun screens) and medicine (diagnostics, drug delivery). This width reflects a diversity of materials that are or will be used in the different applications. Already today, nanotechnology are used for the development or production of a range of products from nano-porous membranes for filtering water (to remove microbes, pollutants or salts), via nano-etched computer chips (to reduce size and energy demand in microprocessors) to silver particle coatings in refrigerators, tennis shoes, band aids, etc. (to kill bacteria and reduce odor problems).
The Royal Society and the Royal Academy of Engineering published an important report in July 2004 (The Royal Society and the Royal Academy of Engineering 2004). Here, concern for negative effects of nanotechnology to both public health and the environment was limited to a single type of nanomaterials, namely engineered nanoparticles in a free form (hereafter abbreviated to ENPs). Most nanomaterials are not particulate, but rather structural larger sized objects. Even engineered nanoparticles are often embedded in a matrix that prevents immediate contact with organisms and release to the environment (e.g. carbon nanotubes embedded in a polymer as structural reinforcement of a golf club or a baseball bat). Contrary to such nanomaterials, ENPs have the potential for spreading in the environment, being taken up by organisms. Some of them have already been shown to have noxious effects on organisms. This report is thus limited to treating ENPs, their fate in the environment and their toxicological properties to ecologically relevant organisms.
It is still a possibility that other nanomaterials, and ENPs embedded in various matrices, could reach the environment and cause environmental concern. This would be possible if the handling of such materials during recycling or as waste leads to fragmentation and significant spreading into the environment. The risks associated with such issues will depend on a wide range of currently unknown parameters such as; what kind of future applications different nanomaterials will have; their tendency to end up in untreated waste; their propensity to fragmentation, mobility and reactivity; product labeling; recycling strategies; volumes; etc. It is somewhat premature to treat these issues at the present time because they require that we can easily identify products that contain nanomaterials. To do so, we would also need reliable inventories of production/use which do not currently exist.
10 Nanoparticles and the environment (TA-2304/2007)
5. Definitions
This section defines and explains some terms that are used in nanotechnology. The definitions are derived from different national standardization and nomenclature organizations in the UK and the USA . There is no common internationally adopted terminology on this area, but definitions in e.g. the two sources used here do not differ
significantly.
The definitions below comply with those of the British Standards Institution and/or those of the American Society for Testing and Materials (ASTM 2006; BSI 2005). Some explanations and examples have been added for the purpose of this report.
Nanotechnology. Design, characterization, production and application of structures, devices and systems controlling shape, size and composition at the nanoscale.
Nanoparticle. A sub-classification of ultrafine particles with lengths in two or three dimensions greater than 1 nanometer (nm) and smaller than about 100 nm, and which may or may not exhibit size-related intensive properties.
Natural nanoparticles. Particles with one or more dimensions at the nanoscale originating from natural processes, e.g. soil colloids.
Incidental nanoparticles. Nanoparticles formed as a by-product of man-made or natural processes, e.g. welding, milling, grinding or combustion.
Engineered nanoparticles (less frequently also “manufactured nanoparticles”). Nanoparticles manufactured to have specific properties or a specific composition.
Size-related intensive properties. Physical or chemical properties of a particle that change as a particle size falls below a certain threshold (surface charge, conductivity, color, etc.).
Agglomerate. A group of particles held together by relatively weak forces.
Aggregate. A discrete group of particles in which the various individual components are not easily broken apart.
Ultrafine particles. Term frequently used by those dealing with industrial products, aerosols
and air pollution, and referring to particulate matter smaller than 2.5 micrometer (PM2.5)
11 Nanoparticles and the environment (TA-2304/2007)
Carbon black (CB) is particulate elemental carbon. Often formed in large quantities as a by- product during production of CNTs and fullerenes, but also a major constituent of soot (constituting nearly spherical aggregates) and recovered as a stable fraction upon incomplete combustion of organic matter. It is unlikely that CB will be considered an ENP in the context of human and environmental risk assessment.
Graphene is a sheet-like building block in graphite, and is made up by a single planar layer of carbon atoms arranged in a honeycomb-like lattice structure (see also Figure 2).
12 Nanoparticles and the environment (TA-2304/2007)
6. Crude classification and occurrence of nanoparticles
This section further describes different categories of nanoparticles as a background to understand their behavior and potential impact on organisms and the environment. It also describes levels of existing nanoparticles in the major environmental recipients and some other properties of these recipients as a background for understanding how ENPs may interact with the environment.
Natural nanoparticles have existed since before Life began on Earth. All life forms that have developed have been exposed to at least some types of nanoparticles during their evolution, and they have thus developed mechanisms to tolerate their presence (Buffle 2006). The most common natural nanoparticles are soil colloids, which are constituted of silicate clay minerals, iron- or aluminum oxides/-hydroxides or humic organic matter, including black carbon. Also, airborne nanocrystals of sea salts formed from evaporation of sea water sprays are among the most common natural nanoparticles.
Incidental nanoparticles are largely either of anthropogenic (from grinding of primary or secondary minerals, wear of metal or mineral surfaces, combustion) or pyrogenic (smoke from volcanoes or fires) origin. One of the most abundant ENPs, carbon black, are also formed incidentally, e.g. during fires, and are thus not new to the environment.
Engineered nanoparticles (ENPs) are particles that are produced by man because have specific nanotechnological properties. They can be made of single elements like carbon (C) or Silver (Ag) or a mixture of elements/molecules. Several ENPs are described in paragraph 5, below.
Air contains large numbers of nano-sized particles, frequently reaching concentrations of 10.000-500.000 particles per cm3 (Tardif 2007). Contrary to what most people believe, indoor air is frequently containing higher concentration of particles than out-door air. How to detect a relatively low number of ENPs released into air with such high background levels of other particles is thus a challenging task to which no good methods have yet been developed. This is mainly a problem in relation to surveillance of workers health during manufacturing of ENPs. It may also pose problems if we want to measure e.g. the quantity of ENPs released into the atmosphere or the stratosphere (it is possible that e.g. ENPs with catalytic properties may interfere with gas transformation processes of atmospheric/stratospheric ozone, NOx, etc.).
Water can also be extremely rich in natural nanoparticles in the form of organic and inorganic colloids, mostly originating from soil. These are commonly natural dissolved or condensed humic substances, inorganic colloids (clays, silicate and iron oxides/hydroxides) or humic-mineral complexes formed from these.
13 Nanoparticles and the environment (TA-2304/2007)
Sediments contain particles that are mainly far larger that nanoparticles, as colloids (by definition) are particles that do not settle by sedimentation, even in non-disturbed water. This is true for primary particles (single, free particles that are not aggregated) and agglomerated particles (loose clusters of a few primary particles), but primary particles and agglomerated particles tend to aggregate into larger particles which will fall out by sedimentation when they reach a certain size. This is happening to a large extent e.g. when fresh water hits the higher salt concentrations of the sea or when waste water is treated with Ca-, Fe- or Al-salts in flocculation basins at waste water treatment plants.
Soil is the environmental matrix that is richest in natural nanoparticles, both as primary particles and agglomerates/aggregates. This is due to constant physical/chemical weathering and re-arrangement of its geogenic constituents coupled with a high biological activity that transform both dead organic matter and minerals. Nano- and micron-scale particles, together with humic substances, give soils (and sediments) a high porosity and extremely high specific surface areas (tens to hundreds of square meters per gram). Most of these particle surfaces are charged, but a high number of sites are also uncharged or hydrophobic. The high surface area and the abundance of both charged and hydrophobic adsorption sites vouch for extensive interactions with all introduced dissolved (solutes) and suspended (particles) materials. This is what makes soils and sediments the ultimate recipients and reservoirs of all sorts of particulate matter, and this is where ENPs will ultimately end up if they are not re-used or destroyed. The question that remains is to what extent ENPs can be mobilized or re- suspended from soils and sediments, and herein lies one of the main challenges in environmental risk assessment of spreading ENPs.
14 Nanoparticles and the environment (TA-2304/2007)
7. An overview of different types of ENPs
This section classifies and describes some of the most common types of engineered nanoparticle with respect to composition and properties that influence their anticipated
behavior in the environment. Some ENP, like fullerenes and carbon nanotubes, have hydrophobic properties while others, like oxides, are hydrophilic. These properties will to some extent determine their behavior in the environment.
Engineered nanoparticles are often classified based on their chemical composition, occasionally supplemented with size or morphology characteristics. A crude division is between carbon-based ENPs and mineral ENPs. A more detailed classification distinguish between
• Fullerenes (grouping Buckminster fullerenes, CNTs, nanocones etc.) • Metal ENPs (e.g. elemental Ag, Au, Fe)
• Oxides (or binary compounds when including carbides, nitrides etc.). E.g. TiO2, Fe- oxides. • Complex compounds (alloys, composites, nanofluids etc., consisting of two or more elements) e.g. Cobalt-zinc iron oxide • Quantum dots (or q-dots) are binary or complex compounds often coated with a polymer. They are usually regarded apart due to unique use and composition. Q-dots are ENPs that exhibit size-dependent electronic or optical properties due to quantum confinement. E.g. cadmium-selenide (CdSe) which has light emission peaks that varies according to particle size; green for 3 nm diameter particles, red for 5 nm, etc. Used in electronics/experimental biology/medicine. • Organic polymers (dendrimers, polystyrene, etc.).
Fullerenes are made up of pure carbon, and represent a newly discovered (1985) carbon allotrope (Gr. allos, other, and tropos, manner. Other well known carbon allotropes are diamond and graphite). The simplest fullerene, C60, is a ball made up of 60 C atoms (Figure 1), and resembles a football. These are also known as buckminster fullerenes or “bucky balls”, named after the architect Richard Buckminster Fuller who constructed a range of geodesic spheres and domes with structures resembling the fullerene.
The next stable fullerene is C70 and has an oblong form. This is followed by C74, C76, C78 and so on, to which six-membered rings are added. When grown by vapor deposition, fullerenes form tubes with a spherical end, and are then called carbon nanotubes. Fullerenes are -1 hydrophobic and soluble in organic solvents, like toluene (2.8 mg l for C60). Fullerenes may contain atoms, ions or small clusters inside their spherical structure, and are then called endofullerenes (named e.g. M@C82 for a metal “M” being enclosed by a fullerene consisting of 82 C atoms). The surface of fullerenes may be modified by functionalization (functional groups are attached covalently to a C atom of the fullerene). A common functionalization is
15 Nanoparticles and the environment (TA-2304/2007)
hydroxylation (attaching OH-groups) which renders the molecule (called fullerol) more hydrophilic (Brant et al. 2007b), but other polar adducts will also have the same effect (Angelini et al. 2001). Fullerenes may form highly stable hydrophilic nano-sized aggregates
(n-C60; 100-200 nm diameter) that can exist as stable aqueous suspensions at low (<0.05 M) ionic strength (Brant et al. 2006; Deguchi et al. 2001).
Figure 1. Fullerenes of different size and an endofullerene containing lanthanum. Image from www.photon.t.u-tokyo.ac.jp
Carbon nanotubes (CNTs) are fibrous fullerenes consisting of rolled-up graphene sheets that may or may not be capped at the ends by a half fullerene Q: Approximately how sphere. They can be made e.g. by laser ablation using large is the current production of CNTs? graphite as a starting material or made from CH4 or A: It is difficult to find other carbon containing gases through chemical vapor reliable inventories on deposition. Resulting CNTs may consist of a single this. I have seen figures layer of C (single-walled carbon nanotubes or like 300 metric tons per SWCNT), double layers (DWCNT), or multiple layers year for 2007, but also of C (MWCNT). A specificity of CNTs is that they are somebody who claims light and have high mechanical strength. Also, they that annual production have conductive properties which depend on the was already >800 metric tons in 2002. In our view, symmetry of the C-C bonds (see Figure 2). If one the former figure is too imagines a sheet of hexagons, like in graphene, this low. sheet may be rolled up to form a cylinder with an axis that is parallel to a third of the C-C bonds, or has an angle Φ that deviates from this perpendicular angle. Electric and thermal conductivity of CNTs depend entirely on this angle Φ, and makes different CNTs more or less useful as semiconductors in electronics and a range of other applications. Production of CNTs yields a mixture of configurations, and purification of the different types is a major challenge (Jolivet and Barron 2007). SWCNTs are believed to have superior mechanical strength, and thermal and electric conductivity, compared to MWCNTs.
The hydrophobicity and fibrous structure of CNTs make them prone to aggregation in bundles, termed nanofibres, nanoropes and nanowires, depending on their dimensions
16 Nanoparticles and the environment (TA-2304/2007)
(nanofibres are relatively short and thin, while nanoropes and nanowires are thicker and longer, up to a millimeter scale).
Figure 2. A graphene sheet and resulting nanotubes with armchair- (a), zigzag- (b) and chiral configurations (c). Images from www.seas.upenn.edu and theor.jinr.ru
Carbon black (CB) may be considered an ENP, though CB has been produced and used industrially since long before the era of nanotechnology. CB is a by-product of combustion, and is also formed naturally during fires. CB is e.g. a major constituent of car tires (up to 30% by mass used as a filler) and is frequently also referred to as black carbon or soot. Basically, CB consists of graphene fragments, and as for fullerenes and CNTs, they are very stable against degradation and thus accumulate in the environment. Some reports claim that stable organic matter in soils and sediments is composed of a substantial part of CB, e.g. in the order of 5-10% (Cornelissen et al. 2005). CB has been used as a reference substance (a control treatment) in studies of toxicity and ecotoxicity of CNT and fullerenes (e.g. Cheng et al. 2007) and then display no or far lower toxic effects.
Q-dots are fluorescent semiconductor nanocrystals, commonly made up by a 3-6 nm diameter core of CdS, CdSe, PbSe, CdHg or a range of other metals, and coated by an organic polymer (to protect against oxidation and to permit linking to biologically active moieties, like antibodies). Due to their small size, being smaller than the so called Bohr exciton radius, they can emit light (i.e. photons) with a specific wavelength that is limited by quantum confinement and determined by particle size and composition (i.e. the resulting band gap energy). Within biology/medicine q-dots are mainly used for fluorescence imaging to localize specific cells (e.g. tumor cells) (Michalet et al. 2005).
Other mineral nanoparticles can be made of single elements (Ag, Au, Cu, Fe, etc.), compounds (SiC, Si3N4, WC, etc.), single-metal oxides (Al2O3, TiO2, ZnO, etc.) and multi- element oxides (MgAl2O4, SrTiO3, etc.). The list here is extremely long, and includes ENPs from different preparation methods, with different particle sizes, different degrees of purity,
17 Nanoparticles and the environment (TA-2304/2007)
different coatings, etc. A wide range of these (close to 900 entries ultimo 2007) may be seen e.g. in the database of www.nanowerk.com.
ENPs based on organic C escape some of the concern for potential environmental impact due to the fact that they are composed of degradable polymers, and unless prepared to resist biodegradation will have a short life span once entering the environment. Also, their composition or preparation indicate few or no immediate noxious properties if absorbed by organisms. A series of organic ENPs are developed as liposome, micelle or dendrimer transport cages for pharmaceutical products (targeted drug delivery). These are often designed to degrade without leaving any trace once the drug is delivered in the target tissue. Starch polymers are also the basis for a type of organic ENPs that are used e.g. in biodegradable plastic films, some times combined with other ENPs, like nanoclays to modify permeability properties (see e.g. Avella et al. 2005).
Other nanoparticles that are commonly encountered in the literature are zero-valent iron (nZVI or Fe0) and nanoclays. These are comprised by the mineral nanoparticles described in the paragraphs above, but have been given these popular names due to applications that are under development, and require adapted terminology. The former is often not used as dispersed nanoparticles, but rather as aggregates of Fe/Fe-oxides with a high internal surface or organically coated particles that are exploited for absorption of various environmental pollutants in soil or water (He and Zhao 2007; Tratnyek and Johnson 2006). Nanoclays are chemically and mechanically dispersed clay minerals (natural clays are composed of packages of nanosized layers, 2-50 nm thickness, of silica-, aluminum and/or iron oxides), and the properties that these flat sheets have (e.g. impermeable to gas) can be exploited when mixed into a matrix like a plastic wrapping material (improving storage of foods or other products that are prone to oxidation).
18 Nanoparticles and the environment (TA-2304/2007)
8. How to describe nanoparticles
To be able to compare different research results, it is crucial that the nanomaterials examined are characterized and described as thoroughly as possible. A thorough characterization is also important to be able to develop mechanistic explanations of behavior and effects based on ENP characteristics. The present section will explain some of the most important characteristics that are used to describe ENPs, and that are relevant parameters for studies on fate and ecotoxicity.
Characterization of nanometer sized materials is particularly challenging due to the fact that materials in this size range fall into a gray area where they may, in many cases, behave either as small particles or as large solutes (Brant et al. 2007a). Yet, the most evident parameter to describe for nanoparticles is size, as it can influence a wide range of material properties such as electronic properties, and interactions with light and other types of electromagnetic radiation. Below particle diameters of 10-20 nm, the number of atoms on a particle’s surface starts to constitute a significant fraction of the total number of atoms in a particle, which may lead to a number of changes related to free surface energy (lattice properties, cell parameters etc.) (Rose et al. 2007).
A batch of ENPs is usually not homogeneous in size. Thus, it is often best characterized by an average particle size (APS), or a particle size range. This is a Q: What is a monodisperse suspension? value that is often given by the manufacturer of A: When you add commercially available nanoparticles. Yet, certain nanoparticles to water in a ENPs have defined dimensions, like fullerenes, where bottle and shake it, they the diameter is determined by the number of atoms that may either float around as they contain (e.g. 0.7 nm for C60). Also single-walled single particles (a carbon nanotubes have rather narrow ranges of well mondisperse suspension), or clump together in defined diameters (1-3 nm), while their length can vary 5 aggregates. In the latter a lot (aspect ratios as high as 10 ). For ENPs to remain case, the ENPs will be suspended as single particles in a liquid (i.e. form meta- much less available for stable monodisperse suspensions), most ENPs interactions with surfaces suspensions must be stabilized with surfactants or other and dissolved molecules, coatings. This establishes more or less permanent layers as they would have to be of molecules that envelope the particles, giving them if they should be used in most industrial far larger effective particle size. Further, the size of applications. individual nanoparticles is also poorly relevant when particles are aggregated or agglomerated, making them behave as far larger particles. Thus, for aggregated or agglomerated ENPs, aggregate size and average agglomeration number (AAN), an estimate of the degree of agglomeration in a suspension, may be more useful parameters. Size, together with charge, is among the most
19 Nanoparticles and the environment (TA-2304/2007)
important characteristics of ENPs, as they seem directly linked to both mobility, uptake and toxicity of ENPs (see also paragraph 8).
Aspect ratio is the ratio between the longest diameter of a particle to the shortest perpendicular diameter (e.g. length and diameter of a tube). It describes one of the most important parameters regarding the shape of a particle and is probably affecting both mobility and uptake of ENPs in organisms.
The surface area of ENPs is the total area of both external and internal surfaces available from the outside of a particle. This is an important parameter because all interactions between ENPs and other surfaces or solutes will relate to (or be quantitatively proportional to) the particle’s surface. As mentioned above, the proportion of atoms exposed to a particle surface constitute a significant proportion of the total number of atoms when the diameter of a nanoparticle is smaller than 10-20 nm. Consequently, the reactivity of ENPs increases strongly with decreasing particle size (i.e. with increasing surface area).
Specific surface area is the ratio of the surface area to the mass for a particle.
Crystalinity refers to more or less stable three- dimensional atom arrangements, and is a property that Q: May ENPs be regarded defines many oxide ENPs, as crystal structure may as persistent in the context have several direct and indirect effects on chemical of environmental and morphological parameters like surface area, pollution? charge, aspect ratios, etc. A: Yes, most ENPs may be perceived as persistent Degradability or persistence of ENPs relates to their pollutants because they chemical composition, with organic ENPs being will not be degraded. Mineral ENPs may be biodegradable, other C allotropes being extremely dissolved and change state persistent, and mineral ENPs being more or less from particles to ions, but prone to weathering by oxidation and/or dissolution, with respect to as for corresponding larger sized materials (see also persistence, they are in the treatment of degradability and persistence in many ways analog to paragraph 8 on behavior and ecotoxicity of ENPs metals and heavy metals. below). Fullerenes and carbon nanotubes are similarly
analogs to carbon black Elemental composition is a description of which and soot. elements an ENP is composed of. The purity of ENPs, and concentrations of major contaminants, is often given by the manufacturer.
Surface charge is a measure of a particle’s propensity to interact with charged surfaces and ions. Surface charge of ENPs may be either pH dependant, as in oxide minerals (due to protonation and deprotonation of functional groups), or they may be fixed, as in clays, where this charge results from crystal lattice defects and atomic substitution (Rose et al. 2007).
20 Nanoparticles and the environment (TA-2304/2007)
Surface charge is closely related to hydrophobicity, which is a particle’s capacity to interact with water. Many ENPs are hydrophobic (e.g. non functionalized fullerenes and CNTs), but may be treated to become hydrophilic. Surface charge/hydrophobicity is presumably an important factor which determines ENP behavior in the environment.
Point of zero charge (PZC) is the pH at which the positive and negative charges are balanced (by dissociation of H+ and OH- ions to an embedding liquid) so that there is no net charge making a particle mobile in an electric field. The PZC determines if a given ENP is charged or uncharged (i.e. more or less hydrophilic in an aqueous suspension), meaning that suspension pH may determine its mobility.
In special cases, other parameters may also be examined with more sophisticated equipment, like chemical structure or surface properties using nuclear magnetic resonance (NMR) or speciation studies using synchrotron experiments (EXAFS, XANES). For an in-depth treatment of structural and chemical characterization of ENPs, the reader should consult e.g. Rose et al. 2007, and references therein, from which much of the information above is collected.
21 Nanoparticles and the environment (TA-2304/2007)
9. Methods to describe and detect nanoparticles
A number of methods may be used to characterize materials on a nano scale, and the evolution of analytical equipment with ever increasing resolution is actually what has led us into the nano-era. Some of these may also be used to trace and detect ENPs in more or less complex matrices, like organisms or tissues, air, water, sediments and soils. But the task of detecting and quantifying ENPs in complex environmental
matrices like natural waters, sediments and soils may truly be a challenge. This is both because of the size of ENPs that makes single particles constitute infinitely small amounts of chemicals that require extremely low detection limits, but also due to interactions with environmental constituents that obscure clear analytical signals. Thus, no methods currently exist that can reliably quantify ENPs in the environment. Some tools may still be used to describe and trace ENPs during laboratory experiments with relevant environmental matrices like soils, sediments and water.
9.1 Qualitative methods
Elemental composition of bulk ENPs is measured with standard chemical analysis, like ICP- MS. Mineral ENPs may in many cases be spiked with specific elements (often rare earth elements) as to modify their physical/chemical properties. These may be present in very low amounts and thus difficult to detect. The surface composition of an ENP may differ from its core, either due to functionalization, added coatings or oxidation. Determination of such surface constituents may require more specialized analytical methods, depending on their nature and concentration.
The morphology of pure nanomaterials is frequently described using high resolution scanning electron microscopy (HR-SEM) or high resolution transmission electron microscopy (HR-TEM). These methods permit a direct visualization of nanoparticles (in a dry state, fixed to a support) and can thus provide data on size, shape and structure. HR-SEM can be used for particles as small as 10-20 nm, while HR-TEM can have a resolution below 1 nm. Backscattering and x-ray detection of elements (EELS and EDX) coupled to TEM, which are a common methods to characterize larger objects with respect to composition, may in some cases be sufficiently sensitive to provide data on elemental distribution at a very low spatial scale (several nm) (Rose et al. 2007). Certain speciation issues regarding oxides forming on the surface if mineral ENPs may also be obtained through diffraction measurements during HR-TEM, as illustrated in figure 3 where the presence of CoO on the surface of Co nanoparticles was shown by selected area electron diffraction (SAED) in addition to the anticipated surface oxide layer composed of Co3O4.
Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have resolution down to the atomic level, and permit both three dimensional imaging of nanometer scale
22 Nanoparticles and the environment (TA-2304/2007)
surfaces and the measurement of forces between surfaces at the piconewton scale, both in liquid and gaseous environments.
Figure 3. HR-TEM image of Co/Co3O4 nanoparticles (bar = 5 nm) and associated SAED pattern demonstrating the presence of CoO in the surface oxide layer (from (Oughton et al. (submitted))
Static light and x-ray scattering experiments may be used to characterize particles in suspension with respect to size, shape and agglomeration state. Particle size in dilute suspensions may also be determined indirectly by dynamic light scattering (DLS), based on Brownian motions of nanoparticles (Rose et al. 2007).
Surface charge is often measured as Zeta potential for particles dispersed in a liquid (i.e. electrophoretic mobility, as velocity, when subjected to an electric field). It is essential that the modification of the surface charge is determined as a function of pH and ionic strength. His permits the determination of the point of zero charge (PZC), which is the pH where an ENP dispersion is the least stable and the highest propensity to aggregate (Rose et al. 2007).
ENP surface area is most reliably determined as BET surface area (based on a theoretical model for monolayer gas adsorption developed by Brunauer, Emmet and Teller published in 1938). This is the most widely used method in surface science for the calculation of surface areas of solids by physical adsorption of gas molecules. It includes internal pore space accessible from the particle surface and thus e.g. gives surface areas of hundreds of m2/g for clays and soil organic matter.
9.2 Quantitative methods for measurements in environmental samples
The methods described above are mainly useful for describing ENPs in a pure state or in “clean” systems, and do not permit their recognition in complex mixtures like environmental samples. To do so, some tools exist:
23 Nanoparticles and the environment (TA-2304/2007)
One may detect very small changes in concentration of rare elements like Ag, Au, Ce, etc by chemical analyses (e.g. by ICP-MS) in samples Q: Does this mean that one cannot distinguish between where their background levels are very low, but elements derived from ENPs such analyses do not distinguish between particles and other sources? and dissolved ions (whether these originate from A: Yes. ENPs or other sources).
For Q-dots or aromatic structures, like fullerenes and CNTs which have intrinsic fluorescent properties, detection based on autofluorescence may be used (Cherukuri et al. 2006; Mureau et al. 2007). The presence of large amounts of other compounds that have fluorescence during detection (e.g. complex organic matter) may however hamper the use of such techniques in complex matrices unless removed e.g. by acid digestion prior to analysis.
Fullerenes may be extracted from environmental matrices using organic solvents, and can be quantified by chromatography and UV-vis spectroscopy or HPLC. Recovery of C60 in e.g. soil or sediments may be non-exhaustive, as is commonly observed with other hydrophobic pollutants like polycyclic aromatic hydrocarbons (PAHs).
CNTs may be detected by UV-vis spectroscopy at high concentrations, and their extreme persistence can permit acid digestion of a surrounding matrix to avoid interference in subsequent analyses. Single-walled CNTs can also be detected by Raman spectroscopy due to specific resonance properties which are not present in MWCNTs. This may possibly also be exploited in complex media (M. Glerup, Dept. of Chemistry, Univ. of Oslo, personal communication)
Isotopic labeling of ENPs in laboratory experiments is a powerful tool tracing and quantification. This can be used to describe behavior of certain ENPs in natural waters, sediments and soils, as well as uptake in organisms. Fullerenes, for example, may be produced with either stable (Fortner et al. 2007) and radioactive isotopes (Masumoto et al. 1999; Yamago et al. 1995) and can then be followed by GC-MS and scintillation counting, respectively. For mineral ENPs, one may exploit stable isotopes of elements like Ag, Fe, Si, Ti, W and a range of others (see e.g. (Gulson and Wong 2006), or use neutron activation of another range ENPs. The latter renders the ENPs radioactive and traceable, and may be used in studies on ENP behavior and uptake in complex systems with soils or sediments (Oughton et al. (submitted)).
ENPs with magnetic properties (containing e.g. Fe, Ni, Co, Mn, etc.) may be extracted, detected or even quantified using a strong magnetometer, like the superconducting quantum interference device (SQUID) (E.Mendoza, Catalan Inst. for Nanotechnology, personal communication).
24 Nanoparticles and the environment (TA-2304/2007)
Certain methods for characterization and quantification of natural colloids may also be applied to ENPs if coupled with appropriate detectors, as Q: Is it possible that ENPs described by Nowack and Bucheli (2007). may be transported in air over long distances and fall out in areas remote The lack of tools to detect and quantify ENPs in from the source of natural waters, sediments, soil, waste, sewage sludge, emission? etc., is a major constraint to describe fate, exposure A: Depending on how and risks associated with spreading of ENPs in the ENPs will enter air, and environment. Research efforts in this area are under how they will react with way, and will hopefully gain more funding (and thus atmospheric constituents, it is possible that certain momentum) when it is realized that the lack of such ENPs released to air and tools hamper the advancement is research on other avoid immediate prioritized areas within this field. aggregation and fallout. So: Yes, it is possible, but there are many “ifs”.
25 Nanoparticles and the environment (TA-2304/2007)
10. State-of the-art knowledge on behavior and ecotoxicity of ENPs
The present section summarizes scientific results on behavior and ecotoxicity of ENPs. It also describes some of the basic characteristics of soil, sediments and water that are likely to make ENP far less available to organisms once contact with these matrices are involved. Ecotoxicity studies of ENPs are scarce and difficult to compare, and few have taken into account the modifying effects of soil, sediment and water constituents. Still, data from experiments under simplified conditions indicate that some ENPs are toxic to a number of organisms, even in very low amounts. This concerns fullerenes, silver nanoparticles and q-dots, and to a lesser degree carbon nanotubes, and nanoparticles
of Cu, ZnO, TiO2 and SiO2. To determine if ENPs represent a risk to organisms and the environment, crucial information is lacking regarding mobility, transfer and uptake as affected by environmental matrices.
10.1. Background
To describe what happens with ENPs once released into the environment, we need to consider some key compartments where organisms are likely to be exposed in different ways. Human toxicity studies, with a main focus on workers environments, are primarily considering dispersion and uptake from air, but also direct uptake through ingestion, dermal exposure and in some special cases related to medical use; injections. Environmental issues also concern air, as particulate matter dispersed in air will fall out by gravity once they condense or aggregate and thus reach a certain size. Both in this and other scenarios for spreading ENPs, water may serve as a transport medium and a temporary reservoir for ENPs. Yet, the ultimate recipients for any non-volatile compound or particle spreading in the environment will be sediments and soils.
Sediments and soils are porous environmental matrices composed of a complex mixture of solids, liquids and dissolved compounds. Sediment and soil constituents, like clay and organic matter, typically have large specific surface areas (typically around 300-500 m2/g), and a high electrochemical surface charge that is likely to make them interact with charged particles, like many ENPs. Natural organic matter in water, sediments and soils also contain hydrophobic domains that are likely to interact with hydrophobic ENPs, like fullerenes and CNTs.
Natural organic matter can be divided into two major classes: non-humic substances (polysaccharides, amino acids, etc.) and humic substances. The latter comprise organic macromolecules formed by partial degradation and transformation of recalcitrant plant and microbial polymers. While some of these are water soluble, others may not be dissolved. Soluble humic substances may be subdivided in fulvic acids, which are water soluble at all pH, and humic acids which are defined as humic substances that are insoluble at low pH (<2) but soluble at alkaline pH. Humic and fulvic acids can constitute up to 50% of natural organic matter in sediments (Jones and Bryan 1998). In aqueous solutions, humic and fulvic acids
26 Nanoparticles and the environment (TA-2304/2007)
exist as dissolved macroligands at low concentrations, and as aggregates at higher concentrations (Gaffney et al. 1996).
Both natural waters in lakes and steams, and pore water in sediments and soils contain natural colloids (dissolved organic carbon, mineral colloids) and dissolved ions. Dispersed colloids are particles in the ENP range (1-200 nm) that are kept in a stable suspension in water. They do not precipitate by gravitation due to their small size, a certain surface charge, and the fact that electrostatic interactions, van der Waals forces and steric forces maintain a stable suspension. Any changes in Q: What is meant by “particle stability”? Are such a system with respect to pH, ion concentrations, nanoparticles unstable? etc. may destabilize the situation. According to classical A: This refers to double-layer and colloid stability theories (O'Melia nanoparticles in 1972), particle stability is affected by the concentration suspension. A stable of cations (coagulants), meaning that at increasing salt suspension keeps particles concentrations free nanoparticles will start to aggregate. floating, but if it is This is typically a process that occurs when river water destabilized the particles will e.g. aggregate and fall reaches the high salt concentrations of sea, or when Ca-, out by sedimentation. Fe- or Al salts are added to waste water in water treatments plants, to induce flocculation and sedimentation.
Releasing ENPs into such complex systems is bound to lead to a range of interactions, and it is not evident whether a given ENP will be adsorbed to a surface or if it is stabilized by natural polymers so that it remains mobile.
10.2. Mobility of ENPs
The production, use and imperfect waste treatment of nanomaterials and their derived products will inevitably lead to losses where nanomaterials end up in the environment, i.e. in water, sediments and soil (Nowack and Bucheli 2007).
Three aspects seem important when assessing the impact of ENPs as pollutants ending up in the environment: 1) Mobility (transport and transfer); their ability to move from one place to another (e.g. from a spill site to an uncontaminated site) or from one recipient to another (e.g. from soil to drinking water or food plants) 2) Ecotoxicity; the possible harm that ENPs can cause to organisms living in water, sediments and soils that they enter. 3) Modification; how and to which extent ENPs are modified by contact with the environment (and the consequences of such modifications on ecotoxicity and mobility).
27 Nanoparticles and the environment (TA-2304/2007)
Transport of common environmental pollutants occurs to a large extent through water transport, either directly as dissolved compounds, or by using suspended materials as vectors. For most ENPs, dissolution is low and particle adsorption to surfaces high, so particulates will probably account for most of the transport. Intuitively, small particles in suspension should move easily through a porous medium where the pore size is large compared to the size of the particles, as is the case for ENPs moving through porous media like soils and sediments. This perception is, however, strongly modified by the physical-chemical properties of the ENPs, the solute and the solid surfaces of the matrix it passes through (Brant et al. 2005b). All other factors being equal, smaller particles are in fact not very mobile because their relatively large diffusivity produces more frequent contacts with the surfaces of a porous medium (Wiesner et al. 2006). This would lead to more extensive interactions with these surfaces, and thus particle deposition. Particle deposition and aggregation are closely related phenomena that can be described as a two-step process of particle transport followed by attachment to a surface. In deposition, the surface is a large immobile site, while in aggregation it is another mobile particle of similar or larger size. The physics of particle transport, at least when considering simple shapes like spheres, are well understood and can be modeled. In contrast, the ability to model and predict attachment as a particle approach a surface is far more limited (Wiesner et al. 2006).
Thus, the study of attachment and transport of ENPs through porous media started by taking an applied approach using simplified model systems with e.g. glass beads or quartz sand as a solid phase and pure water as a transport medium. Such experiments have been able to describe and quantify some of the main mechanisms governing mobility of ENPs in porous media. Lecoanet et al. were the first to study mobility of ENPs in porous media (Lecoanet and Wiesner 2004). They used columns packed with glass beads (APS 355 µm) and assessed mobility of three types of fullerenes (fullerol, nC60 and SWCNTs), TiO2 and SiO2 at two different flow rates. Later, the same authors broadened their selection of ENPs, and conducted a similar experiment which also included alumoxane, larger silica ENPs and ferroxane, in addition to the five ENPs from the previous experiment (Lecoanet et al. 2004). Here, they observed a high mobility of fullerol and surfactant-modified SWCNTs (equivalent to 14 and 10 meters migration in an unfractured sand aquifer, respectively). The lowest mobility in this experiment was observed for nC60, which was approximately 100 times lower than for fullerol.
A major determinant for particle mobility is the stability of its suspension. If destabilized, a particle suspension will aggregate, which in turn may lead to massive deposition (Gimbert et al. 2007). Several factors that affect ENP surface potential may destabilize a suspension, including pH changes, increased ion concentration, dilution or degradation of stabilizing agents (surfactants or coatings), etc. (Guzman et al. 2006). On the other hand, nanoparticles have large surface area to volume ratios and potentially high sorption capacities for other aqueous species such as natural organic matter (Brant et al. 2007a; Fukushi and Sato 2005).
As described above, soils and sediments are complex porous media that are likely to constitute natural barriers against transport and remobilization of ENPs. The extent of ENP
28 Nanoparticles and the environment (TA-2304/2007)
mobility in such matrices depends on porosity, surface charge and reactivity of each matrix constituent, and the prevailing physical-chemical conditions. The fate and bioavailability of ENPs dispersed in these systems thus strongly depend on the filtering properties resulting from these conditions (Ryan and Elimelech 1996). Thus, simple porous media are of limited relevance to describe mobility of ENPs in soils and sediments. The organic and mineral compositions and structural heterogeneity of natural media is complex and must be taken into account to understand the transport and fate of nanoparticles under natural conditions.
Practically nothing is known about how ENPs interact with soils and sediments (Oberdörster et al. 2006; Wiesner et al. 2006). Soils, sediments and water bodies contain solid and dissolved matter which can be powerful geosorbents. While some constituents retain hydrophilic, polar substances, others strongly bind hydrophobic, non-polar compounds. Some ENPs, such as fullerenes and carbon nanotubes (CNTs), are non-polar and do not easily disperse or dissolve in water. In this manner they may resemble common hydrophobic organic contaminants, like polycyclic aromatic hydrocarbons (PAH).
Environmental factors like pH and ionic strength (Brant et al. 2005b; Luthy et al. 1997) together with the physical-chemical properties, structure and concentration of ENPs (Huuskonen 2002; Schwarzenbach et al. 2003) may determine whether they are bound within or transported out of soils and sediments. However, interactions with dissolved constituents may also affect their mobility. As described above, dissolved organic matter is a constituent of both surface waters and soil and sediment pore water, and has recently been shown to interact with CNTs in a way that may enhance their dispersion and transport (Hyung et al. 2007). Therefore, this and other possibilities for remobilization of CNTs and other ENPs into the environment need further examination.
10.3. Other aspects affecting the fate of ENPs
Another interesting issue is how redox transformations may influence the transformation and fate of engineered nanoparticles (Wiesner et al. 2006). Redox reactions occur in a wide range of environments, and are important for the degradation of organic matter, for generation of energy by chemolithotrophic organisms, and for the precipitation and dissolution reactions that influence sequestration and mobility of metals. To what extent nanomaterials will be transformed by redox processes in the environment and how these processes may influence toxicity or other hazards of various nanomaterials is still an open question. Due to chemical composition, surface charge and high specific surface area, some ENPs may have a large capacity to adsorb both inorganic and organic pollutants. One important topic is therefore how nanoparticles may influence mobility, bioavailability and degradation of potentially harmful compounds in the environment (PAHs, heavy metals, etc.).
29 Nanoparticles and the environment (TA-2304/2007)
10.4. Degradability
Degradability, or persistence, of ENPs is highly relevant in the context of environmental impact of ENPs, as persistent particles with negative effects may be able to continue having negative effects for a very long time. C-based ENPs, like fullerenes and CNTs, can theoretically be degraded and re-enter the biogeochemical C cycle as CO2. In practice, however, CNTs, and to slightly lesser extent fullerenes, are extremely persistent to both high temperatures (Cataldo 2002), strong acids and photolytic/ozonation attack (Robichaud et al. 2007). They are thus more likely to accumulate in the environment than to disappear. Mineral ENPs are more or less prone to weathering and dissolution, and some mineral ENPs, like ZnO, are known to dissolve over time when exposed to common environmental conditions. Aggregates of mineral ENPs that are e.g. formed during preparation in an aqueous environment may be easily broken up mechanically, as has been demonstrated with Fe2O3 (Xu et al. 2004). The presence of Al2O3 nanoparticles facilitated disruption of inter-particle attractive forces and similar easy mechanical degradation of aggregates was thus also observed in soil samples containing aggregated nano- Fe2O3. Organic polymer-based or polymer-like ENPs, like starch derivatives, dendrimers, etc., are highly biodegradable, and will be degraded rapidly both in the environment and within organisms (this is indeed the functional role of many ENPs in medical applications; that they serve as a transporter cage that is degraded and releasing it’s pharmaceutical content once inside the target tissue). Similarly, organic coatings and surfactants, that are used to disperse ENPs for various applications, are easily degradable in the environment. It is thus likely that organically coated ENPs will be prone to degradation of the coating, and release their core particles upon such degradation. This has been observed e.g. for lipid-coated SWCNTs that were ingested by the crustacean Daphnia magna and stripped of its lipid coating during passage through the intestines (Roberts et al. 2007).
10.5. Toxicity and ecotoxicity, general considerations
Toxicity and ecotoxicity are two quite different concepts. Whereas toxicity focuses on human beings and aims at protecting individuals, ecotoxicity looks at various trophic organism levels and intend to protect populations and ecosystems. Toxicology traditionally assesses adverse effects of a compound once it is absorbed by an organism, while ecotoxicity includes natural uptake mechanisms and the influence of environmental factors on bioavailability (and thereby on toxicity). While a dry, dispersed nanopowder instilled directly into the respiratory tract of an animal is likely
to be absorbed and provoke a maximum of adverse effects, it is not at all evident that the same particles mixed into river water rich in salts, clay and organic matter will be absorbed by the gills of a fish or the filtering apparatus of a mussel. Before they reach such absorbing organs, they may have aggregated or interacted with other particles or solutes in a way that render them far less reactive and perhaps even entirely unavailable for biological absorption.
30 Nanoparticles and the environment (TA-2304/2007)
Toxicity of fine and ultrafine particles in ambient air (atmospheric pollution, coal dust, asbestos, etc.) has a long history which has been exploited to give “nanotoxicity” studies a flying start (Oberdorster et al. 2005). Indeed, large amounts of nanoparticles are naturally present in the atmosphere, including carbon-nanotubes and other fullerene-related nanocrystals (Murr et al. 2004), and already before the nanotechnology era, we understood a lot about what happens when incidental nanoparticles deposit in mammalian airways and lungs, inducing oxidative stress, inflammation and cardiopulmonary disease (Handy and Shaw 2007; Oberdorster et al. 1995).
However, the unique qualities of ENPs, which include size, large specific surface area, reactivity, shape, etc. not only make them interesting for technological applications, but also open the possibility for them to enter organisms and travel through tissues, cells and even into cell organelles in ways that larger particles may not (Kovochich et al. 2007). Thus, a number of studies have appeared in later years that address these questions, using both in vivo and in vitro techniques (see e.g. Oberdorster et al. 2005).
To complement or replace ethically dubious animal instillation experiments, a range of in vitro tests have been developed that have elucidated some major mechanisms involved in response to ENPs. The generation of reactive oxygen species (ROS) is one important toxicity mechanism, as ROS are known to damage cell membranes, cellular organelles, and nucleic acids contained in DNA and RNA (Hoffmann et al. 2007). These studies have also helped develop more ecologically relevant toxicity measurements, as many of the same enzyme systems or other stress indicators may also be targeted in the context of ecotoxicology.
10.6. Reactive oxygen species (ROS)
A radical (or “free radical”) is an atom or group of atoms that have one or more unpaired electrons. Radicals are formed as necessary intermediates in a variety of normal biochemical reactions, but when generated in excess, or not appropriately controlled, radicals can damage a broad range of macromolecules. A prominent feature of radicals is that they have extremely high chemical reactivity, which explains not only their normal biological activities, but how they inflict damage on cells. There are many types of radicals, but those of most concern in biological systems are derived from oxygen, and known collectively as reactive oxygen species (ROS). Oxygen has two unpaired electrons in separate orbitals in its outer shell. This electronic structure makes oxygen especially susceptible to radical formation. ROS include, -· -2· among others: superoxide anion (O2 ), peroxide (O2 ), hydroxyl radical (·OH), and singlet 1 oxygen ( O2), an excited form of oxygen. Oxygen-derived radicals are generated constantly as part of normal aerobic life. They are e.g. formed in mitochondria as oxygen is reduced along the electron transport chain. But despite their beneficial activities, ROS can clearly be toxic to cells. By definition, radicals possess an unpaired electron, which makes them highly reactive and thereby able to damage all macromolecules, including lipids, proteins and nucleic acids.
31 Nanoparticles and the environment (TA-2304/2007)
One of the best known toxic effects of oxygen radicals is damage to cellular membranes (plasma, mitochondrial and endomembrane systems), which is initiated by a process known as lipid peroxidation. Peroxidation of membrane lipids can have numerous effects, including increased membrane rigidity, decreased activity of membrane-bound enzymes (e.g. Na pumps), altered activity of membrane receptors, and altered permeability. In addition to effects on phospholipids, radicals can also directly attack membrane proteins and induce lipid-lipid, lipid-protein and protein-protein cross-linking, all of which obviously have effects on membrane function (Bowen 2003).
Oxidative stress in terms of ROS generation is a parameter that is convenient to measure in the context of toxicity and ecotoxicity, because cells respond to oxidative stress by mounting a number of protective responses that can easily be measured as enzymatic or genetic expression responses (Kovochich et al. 2007). Several in vitro studies on the toxicity of ENPs have shown generation of ROS, e.g. by TiO2 (Long et al. 2006) and fullerenes (Sayes et al. 2005). On the other hand, some authors have found that ENPs, including e.g. fullerenes, may also protect against oxidative stress (Daroczi et al. 2006; Wang et al. 1999). This apparent dichotomy underlines the need for research on nanoparticle-cell interactions and mechanistic aspects of ENP metabolism in organisms and specific cells.
Many ENPs are photochemically active in the sense that they generate excited electrons when exposed to light (e.g.TiO2, ZnO, SiO2, fullerenes). In the presence of oxygen, these electrons can form superoxide radicals by direct electron transfer (Hoffmann et al. 2007). Thus, situations where organisms are simultaneously exposed to ENPs and light (and in particular UV light which is more energetic than visible light) are of particular concern in an ecotoxicity context.
10.7. Ecotoxicity
Ecotoxicity measurements are conducted on different trophic levels including microorganisms, plants, invertebrates and vertebrates, and test systems have been standardized for some organisms and for some exposure conditions. Thus, one may find protocols approved by the OECD or ISO on how to test the adverse effects of e.g. heavy metals or pesticides towards earthworms, daphnia or zebrafish. The standardized protocols specify some physical and physiological conditions (medium composition, age of organisms, etc.) as well as exposure times (e.g. for acute or chronic toxicity) and which endpoints to measure (growth, fecundity, activity of enzymes, expression of genes, etc.).
But there are of course a far wider range of environmentally relevant organisms living in nature that are or may be used in non-standardized methods to test whether a substance has harmful effects on organisms or processes in the environment. Many of these employ microorganisms as test organisms. Microorganisms (mainly bacteria, but also fungi, protozoa and algae) have the advantage that they are ubiquitous and highly diverse (filling a range of habitats and functions), small (permitting miniaturized tests) and with short generation times
32 Nanoparticles and the environment (TA-2304/2007)
(permitting rapid tests). Also, they are in immediate contact with liquids and surfaces and absorb nutrients and other molecules from their environment directly through their cell walls. Many microorganisms are also easy to culture, and easy to extract DNA from. The latter permits identification based on sequencing of DNA and more importantly to describe whether or not (or to which extent) certain genes related to toxicity protection or stress have been activated (expressed). Identification of multiple microorganisms in a single sample through molecular methods (DNA or other) permits us to describe the composition (or diversity) of complex microbial communities and changes in composition due to a suspected harmful agent. Measurements of such changes are often far more sensitive than tests based on isolation, pure culture and testing of individual microorganisms.
Apart from microorganisms, there are many very useful organisms from different environments that may be used in ecotoxicity testing. In water it may be pertinent to use free- living (pelagic) organisms or organism living on or in sediments (benthic organisms) depending on where the suspected harmful agent is found. Further it may be interesting to use organisms of different trophic level (from different steps in a food chain), from primary producers to grazers and predators, as some environmental pollutants may accumulate in the food chain (biomagnification). Test organisms may also be selected from targeted feeding habits (filtration, engulfment of particles, etc.) or possession of sensitive organs, like gills. In soil, organisms may also be selected based on specific modes of exposure (contact, ingestion, prey preferences), specific habitats (surface, shallow or deep sub-surface, aerated or anoxic environments, etc.) or specific functions (denitrification, bioperturbation, etc.). In either water or soil, organisms may also be chosen because they are important for carrying out an ecologically process, e.g. related to biogeochemical cycling of elements.
10.8. Bioassays – taking bioavailability into account
Ecotoxicity strictly means toxicity to environmental relevant organisms, while the term “bioassay” implies that toxicity or stress caused by a compound has been measured in an environmental matrix pertinent to the habitats where the organism live in nature. Exposing a fish to ENPs in pure water (maybe with some added salts) may thus be an ecotoxicity test, while exposing it to ENPs in water containing both salts, dissolved organic carbon (DOC) and other colloidal materials would constitute a bioassay. Needless to say, the latter situation may give very different results from the first due to interaction between ENPs and dissolved/colloidal materials, as discussed under the paragraph on fate. So far, most ecotoxicity studies of ENPs have not included the modifying effect of environmental matrices, and thus need to be complemented with bioassays.
The modification of ENPs after entering in contact with environmental matrix constituents, like ions, natural colloids and other charged surfaces (see paragraphs 8.2. – 8.4.), are likely to affect not only mobility, aggregation etc., but also to modify toxicity characteristics (Lyon et al. 2007). Further, an ENP that interacts with e.g. a charged surface of a larger particle may not be available for absorption in the same way or to the same extent as a freely suspended
33 Nanoparticles and the environment (TA-2304/2007)
ENP, rendering it less bioavailable. Consequently, a far lower exposure to ENPs may be observed in an environmental matrix compared to what is experienced in vitro.
In addition to this, there is a wide range of environments that will surely differ with respect to interactions with different ENPs, and a wide range of organisms with different feeding habits (exposure routes), trophic levels and niche preferences that will need individual considerations with respect to potential impact.
Like traditional toxicology, ecotoxicology may also use a wide range of physiological and genetic endpoints, but in addition, ecotox organisms may be assayed on a functional level, which adds to the complexity of such investigations.
Toxicity data are essential to describe the potential negative effects of ENPs. They can be used to establish precaution lists or a classification of ENPs for which special measures should be taken, e.g. for protection of workers during production and handling. In an environmental context it is equally important to know ENPs behave when entering in contact with the environment. Such knowledge can be used to predict where ENPs end up, if they are bioavailable, and whether they remain toxic after interacting with common constituents of environmental matrices (dissolved or condensed organic matter, mineral colloids and clays, dissolved salts, etc.).
Most studies on the adverse affects of ENPs have used very pure systems with few possible interactions between ENPs and matrix constituents affecting bioavailability. Thus, the conclusions that may be drawn from these results must acknowledge the fact that environmental constituents in water, soil and sediments (dissolved organic matter, condensed humic substances, clays, etc.) is likely to affect bioavailability and thus toxicity of ENPs.
Having outlined some fundamental concepts in ecotoxicology, we now turn to a presentation of research results on the ecotoxicity of ENPs reported in the literature.
10.9. Ecotoxicity of C60 fullerenes
C60 fullerenes have been among the first ENPs to be investigated with respect to ecotoxicity, starting with the pioneer work of Eva Oberdörster and colleagues. In Oberdörster’s first report on fullerene toxicity (Oberdörster 2004), she showed that low concentrations of C60 (0.5 mg/l) could cause oxidative damage (lipid peroxydation in the brain) and enzyme changes (glutathione reduction in gills) in fish (large mouth bass; Micropterus salmoides). In these experiments, C60 had been dissolved using the organic solvent tetrahydrofuran (THF) and mixed with water before evaporating the solvent to obtain an aqueous suspension of colloidal
C60 aggregates called nC60. Later it was demonstrated that nC60 dissolved with THF trap the solvent within its aggregate structure, and may release this for prolonged periods of time, giving rise to toxicity responses that should not be attributed to the C60, but rather to THF (Brant et al. 2005a). Alternative methods exist for preparing nC60 (Lyon et al. 2006), and
34 Nanoparticles and the environment (TA-2304/2007)
subsequent experimental data were mostly obtained with such methods, excluding confounding effects of THF or other organic solvents.
Comparisons of C60 ecotoxicity to the crustacean Daphnia magna as influenced by mode of C60 preparation have showed that while THF-treated C60 had an LC50 value of 0.46 mg/l and a no observed effect concentration (NOEC) of 0.18 mg/l, sonicated nC60 was far less toxic and had an LC50 value of 7.9 mg/l and a NOEC of 0.2 mg/l (Lovern and Klaper 2006). In later experiments, the same authors observed behavioral changes and increased heart rates in D. magna caused by 0.26 mg/l of THF-treated C60 (Lovern et al. 2007). A functionalized fullerene derivative, C60HxC70Hx, showed even stronger behavioral changes at the same mass- based concentration (0.26 mg/l). Comparisons of the effect of fullerene preparation method (THF solubilization or stirring in water) on ecotoxicity was also compared in an experiment in
Oberdorsters’s lab using daphnia, and showed a 48-h LC50 that was more than one order of magnitude lower for THF-nC60 (0.8 mg/l) than that for water-stirred-nC60 (> 35 mg/l) (Zhu et al. 2006a). These authors also exposed fathead minnow (Pimephales promelas) to the same fullerene preparations, and at 0.5 mg/l this led to 100 % mortality in the case of THF-nC60 within 8-16 h, whereas water-stirred nC60 at the same concentration induced no observable effects even after 48 h. Exposure of another fish species, zebrafish (Danio rerio), to nC60 at 1.5 mg/l delayed embryo and larval development, decreased survival and hatching rates, and caused pericardial oedema (Zhu et al. 2007).
Later experiments by Oberdoster et al. (2006) on the toxicity to daphnia of nC60 prepared without THF showed delayed molting and reduced offspring production at 2.5 mg/l, but could not establish any LD50 for any of their test organisms, as mortality was lower than 50 % at the maximum possible concentrations of C60 (35 mg/l for freshwater and 22.5 mg/l for seawater).
Bacterial tests of the toxicity of C60 fullerenes have shown reduced growth and respiration of at concentrations of <0.4 mg/l and 4 mg/l, respectively, using Escherichia coli and Bacillus subtilis (Fortner et al. 2005). Other studies have shown that bacterial membrane composition and fluidity are sensitive cellular characteristics that are affected by low nC60 concentrations (Fang et al. 2007). Here, Pseudomonas putida decreased its levels of unsaturated fatty acids and increased the proportions of cyclopropane fatty acids in the presence of nC60, possibly to protect the bacterial membrane from oxidative stress. B. subtilis responded to a low dose of nC60 (0.01 mg/l) by significantly increasing the levels of branched fatty acids, and to a high, growth-inhibiting concentration of nC60 (0.75 mg/l) by increasing synthesis of monounsaturated fatty acids. These findings show a physiological adaptation mechanism in bacteria as a response to contact with ENPs. Similar changes have been observed at a higher resolution (community level) in both terrestrial bacteria and protozoa in vivo (Johansen et al.
2008). In the latter experiment bacteria and protozoa were exposed to nC60 at 5-50 mg/kg in soil for 7 or 14 days, and subsequent changes in community structure measured by both culturing and growth independent techniques (PCR amplification of total genomic DNA and separation by DGGE). Changes in community structure were indicative of growth impediment for certain species of the indigenous microbial community, and demonstrated that even in the presence of a highly complexing medium like soil (containing 15 % clay and 2.5
35 Nanoparticles and the environment (TA-2304/2007)
% organic matter), ecotoxicological effects of nC60 may be encountered. A similar approach was used by (Tong et al. 2007) who did not observe any significant effects of 1 or 1000 mg/kg of C60 on the community structure of indigenous soil microorganisms, nor microbial respiration rates or on soil enzyme activities. In the latter experiment, the highest concentration of C60 was introduced in a dry state without any prior suspension in water. The absence of any ecotoxicological effects could indicate that the bioavailability of C60 in the latter experiment was lower in spite of higher total concentrations.
In comparison, one may remark that in vitro genotoxicity studies using human lymphocytes and comet assays have shown toxicity at concentrations as low as 2.2 µg/l for aqueous nC60 (Dhawan et al. 2006).
Fullerols (1 µM) in combination with UV light have been shown to inactivate viruses (bacteriophages) to a far higher extent (100 % increase) than UV light alone (Badireddy et al. 2007). Even dark inactivation was nearly as high as UV light alone. Fullerols have been less toxic than aggregated non-derivatized fullerenes (nC60) in a cytotoxicity study on human cell lines (Sayes et al. 2004). Other derivatized fullerenes, as e.g. the positively charged C60-NH2 inhibited growth, reduced substrate uptake and resulted in damage to cellular structures (cell walls and membranes) in two bacterial species (E. coli and Shewanella oneidensis) at a concentration of 10 mg/l (Tang et al. 2007). In the same study, neutrally charged C60 and C60- OH had milder or no negative effects. Similar results were found by Usenko et al. (2007) using embyonic zebrafish and comparisons of dimethyl sulfoxide suspended and sonicated
C60, C70 and C60(OH)24. Here, exposure to 0.2 mg/l C60 and C70 induced increased in malformations, pericardial oedema and mortality, while the response to C60(OH)24 exposure was less pronounced, even at concentrations one order of magnitude higher. Similarly, Zhu et al. (2007)observed no toxic effects of fullerol (C60OH16-18) at 50 mg/l on zebrafish embryos, while nC60 at 1.5 mg/l showed among others delayed embryo and larval development, and decreased survival and hatching rates.
10.10. Ecotoxicity of carbon nanotubes
Unprocessed single-walled and double-walled carbon nanotubes were investigated for ecotoxicity to zebrafish (Danio rerio) under different salinity conditions (Cheng et al. 2007). SWCNTs induced a significant hatching delay in zebrafish embryos at concentrations greater than 120 mg/l. Double-walled CNTs also induced a hatching delay at concentrations of greater than 240 mg/l, while carbon black did not affect hatching. Embryonic development was not affected at SWCNT concentrations of up to 360 mg/l. The size of the pores on the embryo chorion was nanoscaled while the size of SWCNT agglomerates was microscaled or larger, indicating that the chorion of zebrafish embryos was an effective protective barrier to SWCNT agglomerates. The hatching delay observed in this study likely was induced by the Co and Ni catalysts used in the production of SWCNTs that remained at trace concentrations after purification.
36 Nanoparticles and the environment (TA-2304/2007)
In an experiment with rainbow trout being exposed to dispersed SWCNT prepared using the surfactant sodium dodecyl sulphate (SDS) and sonication, Smith et al. (2007) observed a dose-dependent rise in ventilation rate and gill pathologies (oedema, altered mucocytes, hyperplasia) at concentrations between 0.1 and 0.5 mg/l. SWCNTs precipitated on the gill mucus, and the authors concluded that SWCNTs can act as a respiratory toxicant in trout.
No adverse effects of purified SWCNTs were observed on the estuarine copepod Amphiascus tenuiremis exposed to as much as 10 mg/l in seawater (Templeton et al. 2006). Copepods ingested purified SWNTs, but this had no significant effects on mortality, development or reproduction.
In a study on MWCNT toxicity to the unicellular protozoa Stylonychia mytilus it was observed that CNTs were ingested, redistributed during the dividing process of the cells, and excreted from the cells (Zhu et al. 2006b). Also, exposure to MWCNTs at concentration higher than 1 mg/l induced a dose-dependent growth inhibition of the cells.
A recent study showed that when nanotubes are coated with organic lipids they become more accessible to the water flea Daphnia magna (Roberts et al. 2007). The fleas ingest the materials and strip the lipid layer for food, eventually causing the uncoated nanotubes to block their digestive tracts and kill them.
According to Oberdörster et al. (2006), SWCNTs are less toxic to aquatic organisms than fullerenes. Further, they dismiss the pursuit of CNT toxicity testing until the question of which form(s) of CNTs should be examined, claiming that pure CNTs are not widely used and thus irrelevant in an environmental context. Also, they see reasons to avoid sonication for preparation of aqueous suspensions of CNTs, as they claim that sonication enhances CNT toxicity.
10.11. Ecotoxicity of metal nanoparticles
Silver nanoparticles are mainly produced for antiseptic applications, and they have well documented bacteriocidal (Fu et al. 2006; Jeong et al. 2005) and cytotoxic (Braydich-Stolle et al. 2005) effects, including specific effects on mitochondria and generation of ROS (Hussain et al. 2005). A recent study on uptake of Ag nanoparticles into zebrafish embryos in vivo showed a NOEC as low as 0.19 nM (Lee et al. 2007). Apart from this, data on ecotoxicity of nano silver are scarce.
Copper nanoparticles (particles with a biphasic size distribution broadly peaking at 80 and 450 nm) have been investigated for toxicity towards zebrafish (D. rerio) and compared to toxicity response towards soluble Cu ions (CuSO4) in dechlorinated tap water with a hardness of 142 mg CaCO3/l and a pH of 8.2 (Griffitt et al. 2007). In this study, Cu ENPs were less toxic than Cu ions, with a static LD50 after 48h of 0.25 mg/l for Cu ions and a corresponding value of 1.56 mg/l for Cu ENPs. Exposure to both Cu formulations caused similar gill injuries
37 Nanoparticles and the environment (TA-2304/2007)
(proliferation of epithelial cells and oedemas in primary and secondary gill filaments) and elevated gill Cu concentrations, but Cu ENPs resulted in higher expression levels of several genes related to oxidative stress in gills (but not in liver cells) compared to Cu ions. Cu ENPs are used as an antimicrobial agent in a similar way as Ag (Cioffi et al. 2005a; Cioffi et al. 2005b).
No data are available on the ecotoxicity of gold nanoparticles. Gold nanoparticles are widely used in biomedical imaging and diagnostic tests, and based on the chemical stability of Au0, such use of gold nanoparticles is assumed to be safe. A recent cytotoxicity study on Au nanoparticles ranging in size from 0.8 to 15 nm showed that several human cell types were sensitive to the smallest gold particles (≤1.4 nm) with EC50 values for cell death within 12 h ranging from 30 to 56 µM (Pan et al. 2007).
10.12. Ecotoxicity of oxide nanoparticles
Ecotoxicity of THF-treated titanium oxide (TiO2) to Daphnia magna was measured by (Lovern and Klaper 2006) who found LC50 of 5.5 mg/l after 48 h exposure. NOEC values were between 0.2 and 1 mg/l. Parallel treatments with TiO2 prepared by sonication showed a maximum mortality of 9 % for any TiO2 concentrations up to 500 mg/l.
The ecotoxicity of TiO2 (APS 330 nm), SiO2 (APS 205 nm), and ZnO (APS 480 nm) ENPs to Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria in water suspensions containing citrate and low PO4 concentrations was investigated by Adams et al. (2006). Exposure to these ENPs in sunlight for 6 hours was harmful to varying degrees, with antibacterial activity increasing with particle concentration (tested range 10-5000 mg/l).
Antibacterial activity generally increased from SiO2 to TiO2 to ZnO, and B. subtilis was most sensitive to such effects. Concentration effects were observed for all ENPs up to the highest concentrations (5000 mg/l), except for ZnO which showed high and constant inhibition of B. subtilis at all concentrations from 10 mg/l. Bacterial growth inhibition was also observed under dark conditions where ROS production was expected to be low.
In an ecotoxicity experiment with algae (Desmodesmus subspicatus) and daphnia (D. magna) exposed to pre-illuminated TiO2 showed that algae were the most sensitive of the two, with an EC50 of 44 mg/l (Hund-Rinke and Simon 2006). In this experiment, enhanced toxicity induced by pre-illuminating TiO2 particles shows that the photocatalytic activity of nanoparticles can last for a period of time. How long remains an open question.
Phytotoxicity of ENPs has been demonstrated for Zn and ZnO as inhibition of seed germination and root growth after 2 h exposure to ENP suspensions in deionized water (Lin and Xing 2007). Five types of nanoparticles (multi-walled carbon nanotubes, aluminum, alumina, zinc, and zinc oxide) and six plant species (radish, rape, ryegrass, lettuce, corn, and cucumber) were screened. Fifty percent inhibition of root growth (the most sensitive parameter) was observed for nano-Zn and nano-ZnO at approx. 50 mg/l for radish, and about
38 Nanoparticles and the environment (TA-2304/2007)
20 mg/l for rape and ryegrass, whereas other ENP-plant combinations showed weaker inhibition.
10.13. Ecotoxicity of other nanoparticles
Quantum dots (q-dots) is a diverse group of substances with different composition, size and coatings increasingly used in drug targeting and biomedical imaging. Some q-dots have a strong cytotoxic effect (Hardman 2006), but data on ecotoxicity are lacking. The low amounts necessary for detection of q-dots in medical imaging etc and stringent policies for recovery of medical waste in hospitals indicate that loss of q-dots to the environment will be very low.
Dendrimers are repeatedly branched organic molecules occasionally used to form hollow cages for transport of drug or other therapeutic agents in nanomedicine. There has been some indication that dendrimers display cytotoxicity (Duncan and Izzo 2005), and that cationic dendrimers were more cytotoxic and hemolytic than anionic or PEGylated dendrimers (Chen et al. 2004). No ecotoxicity studies have so far been performed on dendrimers as ENPs.
39 Nanoparticles and the environment (TA-2304/2007)
11. Exposure to ENPs
Exposure may be divided in external exposure (how much ENPs are present in a bioavailable form in the living environment of an organism) and internal exposure (how much ENPs are taken up by an organism, to what extent are these metabolized/transformed/modified and transferred to different organs and tissues, and how long is the residence time within a tissue or an organism before the ENPs are finally excreted). Studies of external exposure require measurements of environmental concentrations, speciation and mobility, whereas studies on internal exposure need to quantify uptake, metabolism and excretion of ENPs. The methodological difficulties in detection, quantification and speciation described in the previous sections indicate that exposure measurements will be inherently complicated.
So far, only controlled experiments exist, where a given external exposure is assumed based on the quantities and forms of ENPs added to a system. Most of the available data concern exposure of aquatic organisms (fish, daphnia and protozoa) to defined concentrations of fullerenes, CNTs, TiO2, Cu and ZnO. The quantities that have been used are in the range 0.01 - 1000 mg/l for fullerenes, 20 – 360 mg/l for SWCNT, 0.1 – 200 mg/l for MWCNT, 10 - 5000 mg/l for TiO2, 0.25 – 1.5 mg/l for Cu and 20 - 2000 mg/l for ZnO. These experiments have used more or less purified water (deionized water, dechlorinated tap water, reconstituted hard water), but avoided inclusion of complex compound like dissolved organic carbon (DOC). Thus, exposure was not modified significantly by the medium composition and these experiments do not permit conclusions beyond simplified dose-response relationships and mechanistic aspects of toxicity (though this is already a good starting point for ecotoxicity considerations).
The factors that influence external exposure are in some cases the same as those that affect mobility, and it is thus likely that e.g. in aqueous environments, increasing salt concentrations leading to ENP aggregation will reduce external exposure, while ENP association with dissolved organic matter in a manner that enhance mobility (Hyung et al. 2007) will lead to enhanced the external exposure.
Internal exposure has been tentatively described in earthworms (Eisenia fetida) which were given cobalt- Q: Is anything known ENP enriched food (Oughton et al. (submitted)). Using about biomagnification of a new technique that render ENPs radioactive, it was ENPs? possible to visualize and quantify ENPs inside different A: No, but this would be a body segments, spermatogenic cells, blood and very interesting question cocoons, and monitor the excretion during a period of 8 to pursue. weeks after transferring the worms to an environment free from ENPs. The results from this preliminary
40 Nanoparticles and the environment (TA-2304/2007)
study indicate that metallic ENPs are excreted very slowly (only about 10 % of absorbed ENPs were excreted after 8 weeks), meaning that internal exposure can be considerable and that bioaccumulation may take place. For MWCNTs, ingestion, internal redistribution during cell division and excretion have been observed in the protozoa Stylonychia mytilus (Zhu et al. 2006b). Here, excretion rates were not estimated, but CNTs were observed within mitochondria, demonstrating that exposure of specific organelles could potentially be detailed and linked to observed damage or quantifiable physiological processes controlled by the organelles in question.
Until more data are available, the question of exposure in complex media will remain open.
41 Nanoparticles and the environment (TA-2304/2007)
12. Environmental hazards and risks
12.1 Background
Risk assessment of ENPs has started with identification of hazards and exposure routes for humans in a production setting, as this is perhaps the most imminent situation where safety issues have to be resolved permit other areas of nanotechnology to advance (Kreyling et al. 2006; Lam et al. 2006). Here, some risks may be described, and by limiting such studies to well defined types of materials and a given setting (e.g. production) it is possible to adapt current risk assessment strategies and obtain a useful outcome where hazards and scenarios are identified. This may e.g. relate to the risks for explosion when dealing with extremely reactive ENPs like Fe0 that explode in contact with air, or the risk for inhalation exposure of workers at production and packaging work stations with dry nanopowders in an industrial setting.
It is premature to attempt the assessment of environmental risks at the present time, and it may indeed never be possible to provide any generally valid risk assessment model for ENPs, as they comprise such a broad and continuously developing class of substances (Colvin 2003). Current approaches for environmental risk assessment of chemicals basically compare (predicted) environmental concentrations to no adverse effect levels. We may assume that a similar strategy can be applicable to evaluate the environmental impact of released ENPs, if speciation- and concentration-dependent exposure and toxicity are taken into account. But as discussed in the chapters above, speciation may change rapidly, and concentrations may not be the appropriate basis for estimating hazards and environmental effects. Furthermore, ENPs might change the environment without being toxic in the traditional sense.
It should also be kept in mind that nanotechnology can have many positive effects also on the environment (sustainable energy, remediation, more efficient products), and that any possible negative effects and risks should be weighed against these benefits during risk assessment.
Risk assessment terminology
Hazard – potential to cause harm Risk – likelihood that potential being realized Environmental risk assessment – risk assessment for both humans and wildlife
Ecological risk assessment – risk assessment for ecological systems
42 Nanoparticles and the environment (TA-2304/2007)
12.2 Environmental risk assessment of nanoparticles
12.2.1 Overview Risk assessment is the task of characterizing a level of risk, usually in terms of a relative score or ranking. The goal of performing a risk assessment is to provide information that will help evaluate alternatives and arrive at decisions (Calow 1998). Traditionally the risk assessment is divided into four steps: 1. Hazard assessment 2. Dose-response assessment 3. Environmental exposure assessment 4. Risk characterization The first step is to identify and characterise the hazards, establish the relationship between dose and response for various endpoints, and then predict the likelihood of exposure. When both dose-response and exposure is quantified, they are compared to characterise the relative risk. In this chapter the different steps of risk assessment is discussed with focus on ENPs.
12.2.2 Hazard assessment In the hazard assessment, the potential of the nanoparticle to cause harm is evaluated. Many considerations should be made when characterizing hazards, e.g. how much is known about the biological uptake and metabolism, which kinds of toxicological studies have been performed (in-vitro/in-vivo, ecotoxicity), which effects have been observed (mortality, mutations, inflammation, irritation, growth reduction, reproductive effects, stress, etc.), are there other end-points of concern, are the data from experiments taking into account realistic exposure mechanisms, etc. When it comes to nanomaterials a lot of these (and other) considerations have not been done and the answers are missing due to lack of investigations. Hazards, such as toxicity and ecotoxicity, can be measured using different endpoints, including physiological, genetic or functional effects, either acute or chronic, etc. But there may also be other potentially negative environmental effects apart from toxicity that need to be considered in a risk assessment paradigm adapted to ENPs (impact on atmospheric/stratospheric processes, stability of soil, effects on bioavailability of mineral nutrients, etc; see paragraph 10.4 below). Robichaud et al. (2007) lists a wide range of various descriptors or characteristics of nanomaterials that may be useful in a hazard assessment addressing behaviour and toxicity (Table 1).
12.2.3 Dose-response assessment Dose-response assessments follow the hazard identification in the risk assessment process. The establishment of dose-response relationships may involve performing experiments in the laboratory or using mathematical models. However, dose-response relationships may not be straight forward for ENPs, as dose based on mass concentration may be less relevant than
43 Nanoparticles and the environment (TA-2304/2007)
dose based on surface area, and as different ENP preparations may result in differences in surface reactivity, and thus toxicity. As for hazard assessment, dose-response assessments need to take into account all relevant end-points (physiological, genetic and functional). Finally, when it comes to predictions of human effects, animal studies or other replacement tests have to be used if results from epidemiological studies are not available (and this is not the case for ENPs).
12.2.4 Exposure assessment Risk assessment of ENPs must build on a range of foreseen scenarios for their spreading. Such scenarios must be based on known or anticipated figures for quantitative and qualitative parameters related to ENP production, trade/transport and use, coupled with a range of possible routes for loss (accidents, leaks, disposal, wear, etc) and estimates of ENP transformation and persistence. The potential for exposure to nanomaterials begins with the production of these materials (as is the case for chemical compounds). Thus, knowledge on quantitative aspects linked to different production steps, purification, functionalization, conditioning, packaging and transport, as well as losses and waste streams associated with each of these are important. Prediction of industrial release must be based upon knowledge on the day-to-day operations, including the processes that are likely to be the most important for emission rates, e.g. those involving high temperatures and high pressures, high material flows and all waste streams. When considering environmental exposure it is also important to consider the frequency and magnitude of incidents that may lead to release to air, water, and soil (Robichaud et al. 2007). For environmental exposure it is important to have empirical data or procedures to predict the persistence and mobility in air, soil and water. Examples of parameters that may be needed to make predictions on environmental fate is chemical factors like adsorption capacity, degree of aggregation, photolytic degradation, dispersability, interactions with soil particles etc. (Table 1). The tendency of nanoparticles to aggregate is especially important for the environmental persistence and effects - it is still an open question whether we can expect to find individual free nanoparticles in the environment (Robichaud et al. 2007).
Table 1 (see next page) is not an exhaustive list of factors that are necessary for predicting exposure, particularly not in an environmental context. It is important to be aware of the differences in nanoparticles properties and the large differences that may occur due to e.g. aggregation. Methods to characterize many chemical and physical properties of nanoparticles are available today (see chapter 6) and many of the physical properties shown in Table 1 can be determined. The second and third categories of descriptors in Table 1, which are referred to as exposure factors and hazard factors, are similar in that they depend on additional variables beyond the physical-chemical characteristics of the nanomaterials (Robichaud et al. 2007). These factors largely remain to be described.
44 Nanoparticles and the environment (TA-2304/2007)
Table 1: Nanomaterial characteristics, behaviours, and effects that may affect their relative risk
Primary descriptors: Secondary descriptors: Tertiary descriptors: Physical characteristics Exposure Hazard • Added molecular • Adsorption tendency • ROS1 generation groups • Chemical • Ability to cross • Oxidative stress composition blood-brain barrier • Number of particles • Ability to cross • Mitocondrial placenta perturbation • Free or bound in • Degree of • Inflammation matrix aggregation • Size distribution • Ability to travel to • Protein denaturation, upper lung degradation • Shape • Ability to travel to • Breakdown in deep lung immune tolerance • Solubility • Bio-accumulation • Allergenicity potential • Magnetic behaviours • Ability to travel to • Damage to central central nervous nervous system system • Surface area • Interactions with • Cellular/subcellular natural occurring changes chemical species in aqueous phase • Surface charge • Transformation to • Damage to eyes other compounds • Surface coating • Interactions with • Damage to lungs natural soil components • Surface reactivity • Dispersability • Damage to GI tract2 • Thermal conductivity • Excretion from body • Electrical • Irritational effect conductivity • Tensile strength • Proportion of total number of atoms at the surface of a structure • Molecular weight • Boiling point • Optical behaviours 1: ROS - reactive oxygen species. 2: GI – Gastro intestinal tract
45 Nanoparticles and the environment (TA-2304/2007)
The final issue to be considered in the context of environmental exposure is to what degree various nanoparticles are taken up by biota, whether they are metabolised or degraded, and at which rates they are excreted. This is where least data are available, and particularly data that take into account the modifying effects of the environments where organisms live while they are exposed to ENPs.
12.2.5 Risk characterisation Risk characterisation is the final step in the risk assessment procedure, in which the information from the hazard identification, dose-response and exposure steps are considered together to determine and communicate the actual likelihood of risk to exposed populations. The risk is often characterised by comparing the exposure concentration (PEC - predicted environmental concentration) with an exposure level that is assumed to have no effect (e.g. PNEC - predicted no-effect concentration). Important issues in this final step is an evaluation of the overall quality of data, the assumptions and uncertainties associated with each step, and the level of confidence in the resulting estimates.
12.3 Current state of environmental risk assessment of ENPs
According to Robichaud et al. (2007) current tools for risk assessment (and life-cycle analysis) may provide useful guidance for short-term assessments for nanomaterials, as we await more results from studies on exposure and hazards. They describe a method for performing a relative risk analysis of nanomaterials using tools from the insurance industry. As an example they mention XL Insurance, a Swiss company that employs a numerical tool to quantify the relative risk of manufacturing processes with respect to financial liability of the insurer. By focusing on environmental pollution and health risks, this tool may be useful as a first step for making a risk assessment protocol for ENPs. Five nanomaterials (single-walled carbon nanotubes, C60 fullerenes, one variety of quantum dots, alumoxane nanoparticles, and TiO2) were selected based upon their current or near-term potential for large scale production. The assessment focused on the activities surrounding the fabrication of nanomaterials, and a list of input materials, output materials, and waste stream for each step of the fabrication process was developed. The influence of key production parameters such as temperature and pressure, in combination with chemical-physical properties of the materials, the relative risk were calculated based upon factors like volatility, carcinogeneity, flammability, toxicity, and persistence. After a qualitative ranking using these factors, they were combined with an actuarial protocol developed by the insurance industry to make a relative risk ranking. The overall conclusion when it comes to risk, is that there do not seem to be any unusual risk associated with the production of the selected materials (Robichaud et al. 2005). Another starting point is of course to establish a new risk assessment paradigm for ENPs, since descriptions of exposure and toxicity can only partly profit from the knowledge base in environmental chemistry, (eco)toxicology and ecology. As a part of this, it is necessary to
46 Nanoparticles and the environment (TA-2304/2007)
produce an inventory of potential hazards of ENPs on ecosystem structure, integrity and function based on new experimental evidence. The challenges of managing risk in situations where there exists a high uncertainty and variability can benefit from the use of weight of evidence (WOE) methods, like the TRIAD approach for contaminated soils and sediments (Jensen and Mesman 2006; Rutgers and Den Besten 2005). Using this approach, risk assessment will not depend on a uniform discipline, but will profit from a multidisciplinary approach. Multi-criteria decision analysis (MCDA) can then be used for a transparent application of a WOE based on different disciplines (Critto et al. 2007; Semenzin et al. 2007). Linkov et al. (2007) states that the essential contribution of MCDA is the possibility to link limited information on physical and chemical properties with decision criteria and weightings elicited from scientists and managers, allowing visualization and quantification of the trade- offs involved in the decision-making process. Figure 4 summarises the described path for a risk assessment framework that uses existing risk assessment models and characteristics of ENPs (hazard and exposure).
ENP-specific features
Characteristics of ENPs (hazard and exposure)
Development of scaling rules + weighing factors
Conceptual model Integration of old and specific for ENPs new concepts for risk (case by case) assessment of ENPs
Identify unaccounted risk factors for ENPs
Evaluate and fit existing systems to ENPs Existing risk assessment models
Figure 4: Proposed path for constructing an ENP risk assessment framework (adopted from (Robichaud et al. 2007).
Even though human risk assessment for ENPs has been attempted for a number of years both in the EU and the US, hazards, toxicity, and risks are still poorly known. From an environmental perspective, hazard characterization and risk assessment are even less developed. In the environment, one should of course consider exposure and toxicity to a range
47 Nanoparticles and the environment (TA-2304/2007)
of relevant organisms, including the modifying effect of their living environment (soil, sediment, water), which is why environmental risk assessment is a far more complex task which may depend on e.g. scientific consensus on which test systems and environmental parameters that need to be included (Warheit et al. 2007a; Warheit et al. 2007b). Such efforts are under way e.g. through national and international research projects and specifically dedicated working group within the European Commission (SCENIHR; Scientific Committee on Emerging and Newly-Identified Health Risks) and the OECD.
12.4 Challenges in the risk assessment of ENPs
When considering effects of ENPs one must also consider effects on ecosystem functioning and possible effects exerted directly on the matrices that serve as a support for life. A few examples of the latter are the effects that strongly photo-oxidizing ENPs may have on stable organic matter in soil. Such organic matter is very slowly degraded (half life of approx. 1000 years) and constitutes an enormous reservoir of carbon. Increasing the turn-over rate of stable organic matter by no more than 1 % world wide would potentially lead to a CO2 enrichment in the atmosphere that would give a substantial contribution to global warming. Similarly, the impact of ENPs entering soil and modifying it’s hydrophilicity may cause decreased wetability and increased problems with erosion, loss of soil fertility and water pollution. ENPs entering soil, sediments and water may also possibly affect the bioavailability of certain essential nutrients (e.g. phosphate) and lead to modified growth rates for algae, phytoplankton and plants. The same mechanisms may also have positive environmental effects through interactions with environmental pollutants like PAHs and heavy metals, which may become less bioavailable and thus less harmful when sequestered by ENPs (Kostal et al. 2005; Yang et al. 2006).
Yet, the most important issues to be resolved in environmental risk assessment are related to ecotoxicity, exposure and extent of future ENP waste streams ending up in the different environmental compartments (water, sediments, soils, sewage sludge, waste deposits, etc). Numerous ecotoxicity studies are under way world-wide to verify both whether currently available test systems for harmful effect are applicable for describing ENP ecotoxicity, and to standardize such tests for routine screening of new ENPs in the context of legislation and other regulatory efforts. The usefulness of standard ecotoxicity tests is however uncertain (Moore 2006), and these are likely only to assess physiological and genetic endpoints, with ecological functions being ignored. Impairment of ecological functions are by far more serious than e.g. the disappearance or genetic modification of single species, as their ecological function may easily be replaced by functionally related species or communities. Thus it is a major challenge not only to develop adapted ecotoxicity tests, but to include and implement functional assays to establish whether potentially harmful ENPs may have an impact on vulnerable ecosystem processes.
48 Nanoparticles and the environment (TA-2304/2007)
12.5 The European Commission’s efforts on risk assessment of ENPs
The European Commission (EC) has initiated research projects, technology platforms, working groups and other committees that deal with various aspects of public acceptance and risks related to nanotechnology:
The European Commission has, through the EC Action Plan for nanotechnology, implemented the intentions to investigate nanotechnology risks on health and the environment through funding of several research projects within the 6th and 7th Framework Programmes. A number of EU projects are thus concluded or running, and provide EC Research DG and other EC offices with views on research priorities and upto-date input on state-of-the-art.
Needs for standardisation of nanotechnology nomenclature, materials, tests systems etc. is currently treated in CEN (European Committee for Standardization), including aspects of testing nanomaterials for safety and risks. The SCCP (European Commission’s Scientific Committee on Consumer Products) are continuously evaluating consumer products and their major chemical components with respect to potential harm. They have e.g. evaluated the use of TiO2 ENPs in sun screens and judged that this is harmless in contact with skin at concentrations below 25%, irrespective of particle size (SCCP 2007). ZnO ENPs were not approved as a UV blocker, but permitted for use as a colouring agent. EFSA - The European Commission has requested a scientific opinion from the European Food Safety Agency (EFSA) relating to the risks arising from nanoscience and nanotechnologies on food and feed safety and the environment. The request also asks to identify the nature of the possible hazards associated with actual and foreseen applications in the food and feed area and to provide general guidance on data needed for the risk assessment of such technologies and applications. ETPIS – the European Technology Platform on Industrial Safety, is focussing a large part of their efforts on assessment risks for human exposure to ENPs in industrial working environments.
The Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) recently adopted an opinion on "the appropriateness of existing methodologies to assess the potential risks of nanotechnologies". Delivered at Commission's request, the report concludes that current risk assessment methodologies require some modification to deal with hazards associated with nanotech. The report states that "in particular, the existing toxicological and ecotoxicological methods may not be sufficient to address all of the issues arising with nanoparticles". SCENIHR points out that very little is known about the physiological responses to nanoparticles. Therefore, they request that conventional toxicity and ecotoxicity tests undergo modification regarding hazards evaluation and the detection of nanoparticle distribution in the human body and in the environment.
49 Nanoparticles and the environment (TA-2304/2007)
12.6 Norwegian efforts in risk assessment of ENPs
The Norwegian Research Council had published a national strategy for research on nanosciences and nanotechnology (Norwegian Research Council 2006) where health- and environmental risks are included. The establishment of the research programme Nanomat subsequently issued a call where risks were among the priority themes. There are thus currently ongoing research projects where health- and environmental risks are being investigated, but no results on these issues have been published yet.
The Norwegian Technology Board has nanotechnology as a prioritized area. The Norwegian Technology Board informs commercial, public and legislative bodies on several current and potential future implications of nanotechnology, including safety and risks. They recently (22nd of Nov. 2007) held an open national hearing on the topic of risks and environmental impacts of nanotechnology.
The Norwegian Scientific Committee for Food Safety is, through the European Food Safety Agency, taking part in risk evaluations of nanomaterials in contact with food and animal feed.
The Norwegian Pollution Control Authority (STF) is currently participating in working groups on environmental risks of nanotechnology within the OECD and the European Commission, and thereby following international efforts on this area closely.
50 Nanoparticles and the environment (TA-2304/2007)
13. Regulatory efforts
Apart from a US effort to regulate the use of nanosilver, no country has, to our knowledge, made any regulations yet that are imposed to nanomaterial producers or marketers. The feasibility of establishing regulations on this area is however intensely debated and evaluated, both within individual countries, supra-national federations like the EU (e.g through SCENIHR; Scientific Committee on Emerging and Newly Identified Health Risks, EFSA; European Food Safety Authority and CEN; European Committee for Standardization), and in international organizations like OECD and ISO. In general, the applicability of existing laws and the modification or establishment of new ones is limited by the lack of data on properties and use of nanomaterials in consumer products (Franco et al. 2007). These authors also point to the lack of tools for detecting and quantifying nanomaterials, establishment of threshold values that are validated for nanomaterials (as compared to dissolved chemicals), as well as toxicological data.
An important part of the debate on legal requirements for nanomaterials has to do with whether or not they should be considered "new chemicals", and at this point different national regulatory institutions are free to decide about their proper definition of this aspect. In the case of silver nanoparticles, the US has taken initiatives to classify this as a pesticide and are taking steps towards a possible ban. Initially, the US EPA decided that nanosilver-coated household appliances like washing machines were “devices”, escaping the regulations that apply to e.g. chemicals or pesticides. A strong pressure from various organizations, including the Natural Resources Defense Council, the US EPA decided to place nanosilver under the authority of the FIFRA (Federal Insecticide, Fungicide and Rodenticide Act), as it was redefined as an antimicrobial agent (Henig 2007). After transferring this regulatory issue to FIFRA, the US EPA decided to regulate only specific nanosilver products, namely those that state antimicrobial properties. While certain producers had marketed products as “infused with naturally antibacterial silver nanoparticles”, they continued to market and sell the same products (food storage containers) after changing their labeling to “specially treated” or “food stays fresh longer”, thus circumventing the law (Henig 2007).
Regulating the nanotechnology area is not the only possibility to ensure a sustainable development and prevent negative impacts on public health and the environment. This area may also be managed through different oversight initiatives, including stewardship programs developed by the industry, voluntary reporting programs and guidance on safe practices in manufacture and disposal. And indeed, volunteer reporting programs have been established. This is the case e.g. in the US and in the UK. The US EPA thus is proposing a voluntary reporting program, called the Nanoscale Materials Stewardship Program (NMSP). The NMSP proposal encourages companies to voluntarily report to EPA information on existing nanomaterials and nanobased products. The data should include chemical name; physical and chemical properties such as density, melting point, and surface area; expected uses; life cycle; and various byproducts that are likely to be produced during manufacture and use of the
51 Nanoparticles and the environment (TA-2304/2007)
materials (Chatterjee 2007). According to Hansen and Tickner (2007), it is uncertain whether voluntary measures will be sufficient to generate relevant data that can be used for protection of public health and the environment, and they conclude that “the key elements of any voluntary environmental program would be incentives to participate for various stakeholders, agency guidance and technical assistance, signed commitments and periodical reporting, quality of information, and transparency both in design reporting and evaluation”. In their opinion, voluntary environmental programs should be made mandatory no more than three years after their initiation, as to motivate voluntary participation at an early stage where companies may benefit from a head start and the possibility to exert an influence program development (Hansen and Tickner 2007).
52 Nanoparticles and the environment (TA-2304/2007)
14. Future research needs
In our view, the most urgent needs for research related to environmental impact of ENPs is to establish the degree of environmental mobility and bioavailability. These parameters will decide whether ENPs can be taken up and cause harm to various organisms (including plants). This is a prerequisite for ecological damage as well as effects on public health through entry into drinking water and the human food chain.
Research on environmental impact of engineered nanoparticles has merely started, and will face major methodological obstacles regarding detection, characterization and tracing (Hurt et al. 2006), as well as a dilemma on which nanoparticles to be examined. The first is due to the small size of nanoparticles and the complexity of the environments where it should be studied (water, sediments, soils, ecosystems), and the latter to the multitude of engineered nanoparticles that exist and their derivatives (e.g. surface modifications of pristine materials).
The future research needs for environmental impact of nanomaterials may be grouped into:
Metrology - Development of methods to detect and quantify ENPs in air, water and soils/sediments/waste. - Testing and adapting existing protocols for analyses of ENPs. - Establishment of standardized requirements for ENP characterization.
Basic toxicological knowledge on nanoparticles - Dose-response relationships for ENPs of different composition and particle size for well defined target organism/cell types and endpoints. - Toxicokinetics, including translocation, excretion dynamics, acute vs. chronic toxicity, toxicity mechanisms, etc.
Environmental behavior - Mobility in soils, sediments and waste. - Adsorption/desorption behavior in relation to organic, mineral and biological components of soil, sediments and water.
Ecotoxicity - Selection of appropriate terrestrial/aquatic organisms and end-points for judging ENP ecotoxicity (or judging fitness for purpose of existing methods). - Establishing procedures for realistic exposure of organisms to ENPs during ecotoxicity measurements.
53 Nanoparticles and the environment (TA-2304/2007)
- Establishing dose-response relationships, toxicokinetics, including translocation, excretion dynamics, acute vs. chronic toxicity, toxicity mechanisms, etc. (as for basic toxicological studies above).
Consumer-related issues - Inventories of production volumes, use and waste streams. - Behavior and fate of nanomaterials in consumer products.
Risk assessments - Development of a new paradigm for environmental risk assessment that takes ENP specificities into account. - Development of sub-models for site specific risk assessment
There is also a need for compiling results and establishing open databases that can serve the international society and reduce the duplication of research efforts.
In the near future, we will certainly see more attempts to make life cycle assessments of various nanomaterials, and such work has been initiated in spite of weak basis of data materials (Klöppfer et al. 2007).
54 Nanoparticles and the environment (TA-2304/2007)
15. Further reading
An overview of useful web-sites and organizations concerned with environmental and risk-related aspects of nanotechnology, and their activities related to information on these issues.
NanoRisk: a newsletter published by Nanowerk LCC ($ 49/year), presented as “a constructive contribution to the responsible development and use of engineered nanomaterials” (www.nanorisk.org).
Nanoforum: An information website started by the European Commission to provide news items on nanotechnology from across the EU, including information from projects and organizations (www.nanoforum.org).
SafeNano: A web service on health and safety driven by Institute of Occupational Medicine (IOM) in Edinburgh claiming to be “United Kingdom’s premier resource on nanotechnology hazard and risk” (www.safenano.org).
OECD Nanosafety: A program that focuses on the implications of the use of nanomaterials for human health and environment safety, and particularly on testing and assessment methods (www.oecd.org/env/nanosafety).
Nanoproject (Project on Emerging Nanotechnologies): An information site on nanotechnology and consumer issues hosted by the Woodrow Wilson International Center for Scholars and the Pew Charitable Trusts. Contains among others a product database with >500 consumer products based on nanotechnology that are currently on the market in one or more countries around the World. (www.nanotechproject.org and www.wilsoncenter.org/index.cfm?fuseaction=topics.home&topic_id=16619).
The Nanoscale Materials Stewardship Program (NMSP): A voluntary reporting program for nanomaterials producers established by the US EPA (www.epa.gov/oppt/nano/nmspfr.htm).
International Council on Nanotechnology (ICON), based at Rice University, USA, is an international, multi-stakeholder organization whose mission is to develop and communicate information regarding potential environmental and health risks of nanotechnology (http://icon.rice.edu/).
The Center for Biological and Environmental Nanotechnology (CBEN) is a National Science Foundation (NSF) funded Nanoscale Science and Engineering Center (NSEC) at Rice
55 Nanoparticles and the environment (TA-2304/2007)
University. CBEN focuses on research at the interface between "dry" nanomaterials and aqueous media such as biology and the environment (http://cben.rice.edu/).
Nanowerk: A portal with a comprehensive collection of nanotechnology information, including a large nanomaterials database (nanoBASE), a nanotechnology directory with links to laboratories, associations, networks and business-to- business companies involved in nanotechnology (NanoLink) and the newsletter NanoRisk (see above) (www.nanowerk.com).
SCENIHR (The Scientific Committee on Emerging and Newly Identified Health Risks) is an EU advisory committee with a Working Group dedicated to safety of nanomaterials who e.g. recently decided on the EC’s view on nanosized TiO2 and ZnO in sun screens and other cosmetic products.
Danish Ministry of The Environment and the Danish EPA recently published a report on nanotechnological consumer products that gives a pertinent and up to date inventory of the use and applications of different nanomaterials (Stuer-Lauridsen et al. 2007).
56 Nanoparticles and the environment (TA-2304/2007)
16. References
Adams L K, Lyon D Y and Alvarez P J J 2006 Comparative eco-toxicity of nanoscale TiO2, SiO2, and ZnO water suspensions. Water Research 40, 3527-3532. AFSSET 2006 Nanomatériaux - Effets sur la santé de l'homme et sur l'environnement. 248 pp. Agence Francaise de Sécurité Sanitaire de l'Environnement et du Travail, Maisons-Alfort, France. Angelini G, De Maria P, Fontana A, Pierini M, Maggini M, Gasparrini F and Zappia G 2001 Study of
the aggregation properties of a novel amphiphilic C60 fullerene derivative. Langmuir 17, 6404- 6407. ASTM 2006 Standard Terminology Relating to Nanotechnology. American Society for Testing and Materials. Avella M, De Vlieger J J, Errico M E, Fischer S, Vacca P and Volpe M G 2005 Biodegradable starch/clay nanocomposite films for food packaging applications. Food Chemistry 93, 467- 474. Badireddy A R, Hotze E M, Chellam S, Alvarez P and Wiesner M R 2007 Inactivation of bacteriophages via photosensitization of fullerol nanoparticles. Environmental Science and Technology 41, 6627-6632. Bowen R 2003 Hypertexts for Biomedical Sciences. Colorado State University. Brant J, Lecoanet H, Hotze M and Wiesner M 2005a Comparison of electrokinetic properties of colloidal fullerenes (n-C-60) formed using two procedures. Environmental Science and Technology 39, 6343-6351. Brant J, Lecoanet H and Wiesner M R 2005b Aggregation and deposition characteristics of fullerene nanoparticles in aqueous systems. Journal of Nanoparticle Research 7, 545-553. Brant J A, Labille J, Bottero J Y and Wiesner M R 2006 Characterizing the impact of preparation method on fullerene cluster structure and chemistry. Langmuir 22, 3878-3885. Brant J A, Labille J, Bottero J Y and Wiesner M R 2007a Nanoparticle transport, aggregation and deposition. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 231-294. McGraw Hill, New York. Brant J A, Labille J, Robichaud C O and Wiesner M 2007b Fullerol cluster formation in aqueous solutions: Implications for environmental release. Journal of Colloid and Interface Science 314, 281-288. Braydich-Stolle L, Hussain S, Schlager J J and Hofmann M C 2005 In vitro cytotoxicity of nanoparticles in mammalian germline stem cells. Toxicological Sciences 88, 412-419. Breggin L K and Pendergrass J 2007 Where does the nano go? End-of-life regulation of nanotechnologies. 61 pp. Woodrow Wilson International Center for Scholars, Washington DC. BSI 2005 Vocabulary - Nanoparticles. In Publicly Available Specification. 26 pp. British Standards Institution, London. Buffle J 2006 The key role of environmental colloids/nanoparticles for the sustainability of life. Environmental Chemistry 3, 155-158. Calow P 1998 Handbook of Environmental Risk Assessment and Management. Blackwell Science, Oxford. 590 pp. Cataldo F 2002 A study on the thermal stability to 1000 degrees C of various carbon allotropes and carbonaceous matter both under nitrogen and in air. Fullerenes Nanotubes and Carbon Nanostructures 10, 293-311. Chatterjee R 2007 The challenge of regulating nanomaterials. In Environmental Science and Technology Online Policy News – November 14, 2007.
57 Nanoparticles and the environment (TA-2304/2007)
Chen H T, Neerman M F, Parrish A R and Simanek E E 2004 Cytotoxicity, hemolysis, and acute in vivo toxicity of dendrimers based on melamine, candidate vehicles for drug delivery. Journal of the American Chemical Society 126, 10044-10048. Cheng J, Flahaut E and Cheng S H 2007 Effect of carbon nanotubes on developing zebrafish (Danio rerio) embryos. Environmental Toxicology and Chemistry 26, 708-716. Cherukuri P, Gannon C J, Leeuw T K, Schmidt H K, Smalley R E, Curley S A and Weisman B 2006 Mammalian pharmacokinetics of carbon nanotubes using intrinsic near-infrared fluorescence. Proceedings of the National Academy of Sciences of the United States of America 103, 18882-18886. Cioffi N, Ditaranto N, Torsi L, Picca R A, De Giglio E, Sabbatini L, Novello L, Tantillo G, Bleve- Zacheo T and Zambonin P G 2005a Synthesis, analytical characterization and bioactivity of Ag and Cu nanoparticles embedded in poly-vinyl-methyl-ketone films. Analytical and Bioanalytical Chemistry 382, 1912-1918. Cioffi N, Torsi L, Ditaranto N, Tantillo G, Ghibelli L, Sabbatini L, Bleve-Zacheo T, D'Alessio M, Zambonin P G and Traversa E 2005b Copper nanoparticle/polymer composites with antifungal and bacteriostatic properties. Chemistry of Materials 17, 5255-5262. Colvin V L 2003 The potential environmental impact of engineered nanomaterials. Nature Biotechnology 21, 1166-1170. Cornelissen G, Gustafsson O, Bucheli T D, Jonker M T O, Koelmans A A and Van Noort P C M 2005 Extensive sorption of organic compounds to black carbon, coal, and kerogen in sediments and soils: Mechanisms and consequences for distribution, bioaccumulation, and biodegradation. Environmental Science and Technology 39, 6881-6895. Critto A, Torresan S, Semenzin E, Giove S, Mesman M, Schouten A J, Rutgers M and Marcomini A 2007 Development of a site-specific Ecological Risk Assessment for contaminated sites: Part I. A multi-criteria based system for the selection of ecotoxicological tests and ecological observations. Sci. Tot. Environ. (accepted). Daroczi B, Kari G, McAleer M F, Wolf J C, Rodeck U and Dicker A P 2006 In vivo radioprotection by the fullerene nanoparticle DF-1 as assessed in a zebrafish model. Clinical Cancer Research 12, 7086-7091. Deguchi S, Alargova R G and Tsujii K 2001 Stable dispersions of fullerenes, C-60 and C-70, in water. Preparation and characterization. Langmuir 17, 6013-6017. Dhawan A, Taurozzi J S, Pandey A K, Shan W, Miller S M, Hashsham S A and Tarabara V V 2006
Stable colloidal dispersions of C60 fullerenes in water: Evidence for genotoxicity. Environmental Science and Technology 40, 7394-7401. Duncan R and Izzo L 2005 Dendrimer biocompatibility and toxicity. Advanced Drug Delivery Reviews 57, 2215-2237. Fang J S, Lyon D Y, Wiesner M R, Dong J P and Alvarez P J J 2007 Effect of a fullerene water suspension on bacterial phospholipids and membrane phase behavior. Environmental Science and Technology 41, 2636-2642. Fortner J D, Kim D I, Boyd A M, Falkner J C, Moran S, Colvin V L, Hughes J B and Kim J H 2007
Reaction of water-stable C60 aggregates with ozone. Environmental Science and Technology. Fortner J D, Lyon D Y, Sayes C M, Boyd A M, Falkner J C, Hotze E M, Alemany L B, Tao Y J, Guo W, Ausman K D, Colvin V L and Hughes J B 2005 C-60 in water: Nanocrystal formation and microbial response. Environmental Science and Technology 39, 4307-4316. Franco A, Hansen S F, Olsen S I and Butti L 2007 Limits and prospects of the "incremental approach" and the European legislation on the management of risks related to nanomaterials. Regulatory Toxicology and Pharmacology 48, 171-183.
58 Nanoparticles and the environment (TA-2304/2007)
Fu J H, Ji J, Fan D Z and Shen J C 2006 Construction of antibacterial multilayer films containing nanosilver via layer-by-layer assembly of heparin and chitosan-silver ions complex. Journal of Biomedical Materials Research Part A 79A, 665-674. Fukushi K and Sato T 2005 Using a surface complexation model to predict the nature and stability of nanoparticles. Environmental Science and Technology 39, 1250-1256. Gaffney J S, Marley N A and Clark S B 1996 Humic and fulvic acids and organic colloids in the environment. In Humic and Fulvic Acids. Isolation, Structure and Environmental Role. Eds. J S Gaffney, N A Marley and S B Clark. pp 2-16. American Chemical Society, Washington. Gimbert L J, Hamon R E, Casey P S and Worsfold P J 2007 Partitioning and stability of engineered ZnO nanoparticles in soil suspensions using flow field-flow fractionation. Environmental Chemistry 4, 8-10. Griffitt R J, Weil R, Hyndman K A, Denslow N D, Powers K, Taylor D and Barber D S 2007 Exposure to copper nanoparticles causes gill injury and acute lethality in zebrafish (Danio rerio). Environmental Science and Technology 41, 8178-8186. Gulson B and Wong H 2006 Stable isotopic tracing - A way forward for nanotechnology. Environmental Health Perspectives 114, 1486-1488. Guzman K A D, Finnegan M P and Banfield J F 2006 Influence of surface potential on aggregation and transport of titania nanoparticles. Environmental Science and Technology 40, 7688-7693. Handy R D and Shaw B J 2007 Toxic effects of nanoparticles and nanomaterials: Implications for public health, risk assessment and the public perception of nanotechnology. Health, Risk & Society 9, 125-144. Hansen S F and Tickner J A 2007 The challenges of adopting voluntary health, safety and environment measures for manufactured nanomaterials: Lessons from the past for more effective adoption in the future. Nanotechnology Law & Business 4, 341-359. Hardman R 2006 A toxicologic review of quantum dots: Toxicity depends on physicochemical and environmental factors. Environmental Health Perspectives 114, 165-172. He F and Zhao D 2007 Manipulating the size and dispersibility of zerovalent iron nanoparticles by use of carboxymethyl cellulose stabilizers. Environmental Science and Technology 41, 6216- 6221. Henig R M 2007 Our silver-coated future. In Onearth. pp 22-29. Hoffmann M, Holtze E M and Wiesner M R 2007 Reactive oxygen species generation on nanoparticulate material. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 155-203. McGraw Hill, New York.
Hund-Rinke K and Simon M 2006 Ecotoxic effect of photocatalytic active nanoparticles TiO2 on algae and daphnids. Environmental Science and Pollution Research 13, 225-232. Hurt R H, Monthioux M and Kane A 2006 Toxicology of carbon nanomaterials: Status, trends, and perspectives on the special issue. Carbon 44, 1028-1033. Hussain S M, Hess K L, Gearhart J M, Geiss K T and Schlager J J 2005 In vitro toxicity of nanoparticles in BRL 3A rat liver cells. Toxicology in Vitro 19, 975-983. Huuskonen J 2002 Prediction of soil sorption of a diverse set of organic chemicals from molecular structure. Journal of Chemical Information and Modeling 43, 1457-1462. Hyung H, Fortner J D, Hughes J B and Kim J-H 2007 Natural organic matter stabilizes carbon nanotubes in the aqueous phase. Environmental Science and Technology 41, 179-184. Jensen J and Mesman M 2006 LIBERATION, Ecological risk assessment of contaminated land, decision support for site specific investigations. RIVM, Bilthoven, The Netherlands. Jeong S H, Hwang Y H and Yi S C 2005 Antibacterial properties of padded PP/PE nonwovens incorporating nano-sized silver colloids. Journal of Materials Science 40, 5413-5418.
59 Nanoparticles and the environment (TA-2304/2007)
Johansen A, Pedersen A L, Binnerup S J, Karlson U, Hansen B M, Scott-Fordsmand J J and Winding
A 2008 Effects of C60 fullerene nanoparticles on soil bacteria and protozoans. Environmental Toxicology and Chemistry In press. Jolivet J P and Barron A R 2007 Nanomaterials fabrication. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 29-103. McGraw Hill, New York. Jones M N and Bryan N D 1998 Colloidal properties of humic substances. Advances in Colloid Interface Sciences 78, 1-48. Kemikalieinspektionen 2007 Nanoteknik - Store risker med små partikler? In KEMI. Eds. A F Filipsson and C Österwall. 75 pp. Kemikalieinspektionen, Sundbyberg. Klöppfer W, Curran M A, Frankl P, Heijungs R, Köhler A and Olsen S I 2007 Nanotechnology and Life Cycle Assessment. A systems approach to nanotechnology and the environment. 34 pp. Woodrow Wilson International Center for Scholars Washington DC. Kostal J, Prabhukumar G, Lao U L, Chen A, Matsumoto M, Mulchandani A and Chen W 2005 Customizable biopolymers for heavy metal remediation. Journal of Nanoparticle Research 7, 517-523. Kovochich M, Xia T, Xu J, Yeh J I and Nel A E 2007 Principles and procedures to assess nanomaterial toxicity. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 205-229. McGraw Hill, New York. Kreyling W G, Semmler-Behnke M and Moller W 2006 Health implications of nanoparticles. Journal of Nanoparticle Research 8, 543-562. Lam C W, James J T, McCluskey R, Arepalli S and Hunter R L 2006 A review of carbon nanotube toxicity and assessment of potential occupational and environmental health risks. Critical Reviews in Toxicology 36, 189-217. Lecoanet H F, Bottero J Y and Wiesner M R 2004 Laboratory assessment of the mobility of nanomaterials in porous media. Environmental Science and Technology 38, 5164-5169. Lecoanet H F and Wiesner M R 2004 Velocity effects on fullerene and oxide nanoparticle deposition in porous media. Environmental Science and Technology 38, 4377-4382. Lee K J, Nallathamby P D, Browning L M, Osgood C J and Xu X-H N 2007 In vivo imaging of transport and biocompatibility of single silver nanoparticles in early development of zebrafish embryos ACS Nano 1, 133–143. Lin D and Xing B 2007 Phytotoxicity of nanoparticles: Inhibition of seed germination and root growth. Environmental Pollution 150, 243-250. Linkov I, Satterstrom F K, Steevens J, Ferguson E and Pleus R C 2007 Multi-criteria decision analysis and environmental risk assessment for nanomaterials. Journal of Nanoparticle Research 9, 543-554. Long T C, Saleh N, Tilton R D, Lowry G V and Veronesi B 2006 Titanium dioxide (P25) produces reactive oxygen species in immortalized brain microglia (BV2): Implications for nanoparticle neurotoxicity. Environmental Science and Technololgy 40, 4346-4352. Lovern S B and Klaper R 2006 Daphnia magna mortality when exposed to titanium dioxide and fullerene (C-60) nanoparticles. Environmental Toxicology and Chemistry 25, 1132-1137. Lovern S B, Strickler J R and Klaper R 2007 Behavioral and physiological changes in Daphnia magna
when exposed to nanoparticle suspensions (titanium dioxide, nano-C60, and C60HxC70Hx). Environmental Science and Technology 41, 4465-4470. Luthy R G, Aiken G R, Brusseau M L, Cunningham S D, Gschwend P M, Pignatello J J, Reinhard M, Traina S J, Weber W J and Westall J C 1997 Sequestration of hydrophobic organic contaminants by geosorbents. Environmental Science and Technology 31, 3341-3347.
60 Nanoparticles and the environment (TA-2304/2007)
Lyon D Y, Adams L K, Falkner J C and Alvarez P J J 2006 Antibacterial activity of fullerene water suspensions: Effects of preparation method and particle size. Environmental Science and Technology 40, 4360 -4366. Lyon D Y, Thill A, Rose J and Alvarez P J J 2007 Ecotoxicological impacts of nanomaterials. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 445-479. McGraw Hill, New York. Masumoto K, Ohtsuki T, Sueki K, Kikuchi K and Mitsugashira T 1999 Direct synthesis of radioactive carbon labeled fullerenes using nuclear reactions. Journal of Radioanalytical and Nuclear Chemistry 239, 201-206. Michalet X, Pinaud F F, Bentolila L A, Tsay J M, Doose S, Li J J, Sundaresan G, Wu A M, Gambhir S S and Weiss S 2005 Quantum dots for live cells, in vivo imaging, and diagnostics. Science 307 (5709), 538-544. Miljøstyrelsen 2007 Nanoteknologi, miljø og sundhed - ansvarlig udnyttelse af teknologi i udvikling. Eds. B H Andersen, P B Larsen, F Ingerslev and D B Lerche. 36 pp. Miljøstyrelsen, København. Moore M N 2006 Do nanoparticles present ecotoxicological risks for the health of the aquatic environment? Environment International 32, 967-976. Mureau N, Mendoza E and Silva S R P 2007 Dielectrophoretic manipulation of fluorescing single- walled carbon nanotubes. Electrophoresis 28, 1495. Murr L E, Soto K F, Esquivel E V, Bang J J, Guerrero P A, Lopez D A and Ramirez D A 2004 Carbon nanotubes and other fullerene-related nanocrystals in the environment: A TEM study. Journal of Metals 56, 28-31. Norwegian Research Council N F 2006 National Strategy on Nanosciences and Nanotechnology (Nasjonal strategi for nanovitenskap og nanoteknologi, in Norwegian). p. 56, Oslo. Nowack B and Bucheli T D 2007 Occurrence, behavior and effects of nanoparticles in the environment. Environmental Pollution 150, 5-22. O'Melia C R 1972 Coagulation and flocculation. In Physicochemical Processes for Water Quality Control. Ed. W J Weber jr. pp 61-109. Wiley Interscience, New York. Oberdorster E, Zhu S Q, Blickley T M, McClellan-Green P and Haasch M L 2006 Ecotoxicology of carbon-based engineered nanoparticles: Effects of fullerene (C-60) on aquatic organisms. Carbon 44, 1112-1120. Oberdorster G, Gelein R M, Ferin J and Weiss B 1995 Association of particulate air-pollution and acute mortality - Involvement of ultrafine particles. Inhalation Toxicology 7, 111-124. Oberdorster G, Oberdorster E and Oberdorster J 2005 Nanotoxicology: An emerging discipline evolving from studies of ultrafine particles. Environmental Health Perspectives 113, 823-839. Oberdörster E 2004 Manufactured nanomaterials (Fullerenes, C60) induce oxidative stress in the brain of juvenile largemouth bass. Environmental Health Perspectives 112, 1058-1062. Oberdörster E, Zhu S Q, Blickley T M, McClellan-Green P and Haasch M L 2006 Ecotoxicology of carbon-based engineered nanoparticles: Effects of fullerene (C-60) on aquatic organisms. Carbon 44, 1112-1120. Oughton D H, Hertel-Aas T, Pellicer E, Mendoza E and Joner E J (2008) Neutron activation of engineered nanoparticles as a tool in studies on their environmental fate and uptake in organisms. Environmental Toxicology and Chemistry, accepted for publication. Pan Y, Neuss S, Leifert A, Fischler M, Wen F, Simon U, Schmid G, Brandau W and Jahnen-Dechent W 2007 Size-dependent cytotoxicity of gold nanoparticles. Small 3, 1941-1949. Roberts A P, Mount A S, Seda B, Souther J, Qiao R, Lin S, Ke P C, Rao A M and Klaine S J 2007 In vivo biomodification of lipid-coated carbon nanotubes by Daphnia magna. Environmental Science and Technology 41, 3025 - 3029.
61 Nanoparticles and the environment (TA-2304/2007)
Robichaud C O, Tanzil D, Weilenmann U and Wiesner M R 2005 Relative risk analysis of several manufactured nanomaterials: An insurance industry context. Environmental Science and Technology 39, 8985-8994. Robichaud C O, Tanzil D and Wiesner M R 2007 Assessing life-cycle risks of nanomaterials. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 481-524. McGraw Hill, New York. Rose J, Thill A and Brant J 2007 Methods for structural and chemical characterization of nanomaterials. In Environmental Nanotechnology. Applications and Impacts of Nanomaterials. Eds. M R Wiesner and J Y Bottero. pp 105-154. McGraw Hill, New York. Rutgers M and Den Besten P 2005 Approach to legislation in a global context, B. the Netherlands perspective - soils and sediments. In Environmental toxicity testing. Eds. K C Thompson, K Wadhia and A P Loibner. pp 269-289. Blackwell Publishing CRC Press, Oxford. Ryan J N and Elimelech M 1996 Colloid mobilization and transport in groundwater. Colloid Surface A 107, 1-56. Sayes C M, Fortner J D, Guo W, Lyon D, Boyd A M, Ausman K D, Tao Y J, Sitharaman B, Wilson L J, Hughes J B, West J L and Colvin V L 2004 The differential cytotoxicity of water-soluble fullerenes. Nano Letters 4, 1881-1887. Sayes C M, Gobin A M, Ausman K D, Mendez J, West J L and Colvin V L 2005 Nano-C-60 cytotoxicity is due to lipid peroxidation. Biomaterials 26, 7587-7595. SCCP 2007 Preliminary opinion on safety of nanomaterials in cosmetic products. 56 pp. European Commission's Scientific Committee on Consumer Products. Schwarzenbach R P, Gschwend P M and Imboden D M 2003 Environmental Chemistry. John Wiley and Sons, New Jersey. Semenzin E, Critto A, Rutgers M and Marcomini A 2007 Development of a site-specific Ecological Risk Assessment for contaminated sites: Part II. A multi-criteria based system for the selection of bioavailability assessment tools. Sci. Tot. Environ. (accepted). Smith C J, Shaw B J and Handy R D 2007 Toxicity of single walled carbon nanotubes to rainbow trout, (Oncorhynchus mykiss): Respiratory toxicity, organ pathologies, and other physiological effects. Aquatic Toxicology 82, 94-109. Stuer-Lauridsen F, Kamper A, Borling P, Petersen G I, Hansen S F and Baun A 2007 Survey of nanotechnological consumer products. 68 pp. Environmental Protection Agency, Danish Ministry of the Environment. Tang Y J J, Ashcroft J M, Chen D, Min G W, Kim C H, Murkhejee B, Larabell C, Keasling J D and Chen F Q F 2007 Charge-associated effects of fullerene derivatives on microbial structural integrity and central metabolism. Nano Letters 7, 754-760. Tardif F 2007 Nanoparticle monitoring. State of the art and development strategies In HUB meeting of the European Technology Platform for Industrial Safety, Brussels. Templeton R C, Ferguson P L, Washburn K M, Scrivens W A and Chandler G T 2006 Life.cycle effects of single-walled carbon nanotubes (SWNTs) on an estuarine meiobenthic copepod. Environmental Science and Technology 40, 7387-7393. The International Risk Governance Council 2006 White paper on nanotechnology and risk governance. Eds. O Renn and M Roco. 108 pp, Geneva. The Royal Society and the Royal Academy of Engineering 2004 Nanoscience and nanotechnologies: Opportunities and uncertainties. 111pp. The Royal Society and the Royal Academy of Engineering, London.
Tong Z, Bischoff M, Nies L, Appelgate B and Turco R F 2007 Impact of fullerene (C60) on a soil microbial community. Environmental Science and Technology 41, 2985 - 2991.
62 Nanoparticles and the environment (TA-2304/2007)
Tratnyek P G and Johnson R L 2006 Nanotechnologies for environmental cleanup. Nano Today 1, 44- 48. UNEP 2007 Emerging challenges - The environmental risks of nanotechnology. In The GEO Year Book 2007. An overview of our changing environment. pp 61-70. United Nations Environment Programme, Washington DC. US-EPA 2007 US Environmental Protection Agency Nanotechnology White Paper. Eds. J G Morris and J Willis. 132 pp, US Environmental Protection Agency. Usenko C Y, Harper S L and Tanguay R L 2007 In vivo evaluation of carbon fullerene toxicity using embryonic zebrafish. Carbon 45, 1891-1898. Wang I C, Tai L A, Lee D D, Kanakamma P P, Shen C K F, Luh T Y, Cheng C H and Hwang K C 1999 C-60 and water-soluble fullerene derivatives as antioxidants against radical-initiated lipid peroxidation. Journal of Medicinal Chemistry 42, 4614-4620. Warheit D B, Borm P J A, Hennes C and Lademann J 2007a Testing strategies to establish the safety of nanomaterials: Conclusions of an ECETOC workshop. Inhalation Toxicology 19, 631-643. Warheit D B, Hoke R A, Finlay C, Donner E M, Reed K L and Sayes C M 2007b Development of a
base set of toxicity tests using ultrafine TiO2 particles as a component of nanoparticle risk management. Toxicology Letters 171, 99-110. Wiesner M R, Lowry G V, Alvarez P, Dionysiou D and Biswas P 2006 Assessing the risks of manufactured nanomaterials. Environmental Science and Technology 40, 4336-4345. Xu M, Bahl C R H, Frandsen C and Morup S 2004 Interparticle interactions in agglomerates of a-
Fe2O3 nanoparticles: influence of grinding. Journal of Colloid and Interface Science 279, 132- 136. Yamago S, Tokuyama H, Nakamura E, Kikuchi K, Kananishi S, Sueki K, Nakahara H, Enomoto S and Ambe F 1995 In vivo biological behavior of a water-miscible fullerene - C-14 labeling, absorption, distribution, excretion and acute toxicity. Chemistry & Biology 2, 385-389. Yang K, Zhu L Z and Xing B S 2006 Adsorption of polycyclic aromatic hydrocarbons by carbon nanomaterials. Environmental Science and Technology 40, 1855-1861. Zhu S Q, Oberdorster E and Haasch M L 2006a Toxicity of an engineered nanoparticle (fullerene, C- 60) in two aquatic species, Daphnia and fathead minnow. Marine Environmental Research 62, S5-S9. Zhu X S, Zhu L, Li Y, Duan Z H, Chen W and Alvarez P J J 2007 Developmental toxicity in zebrafish (Danio rerio) embryos after exposure to manufactured nanomaterials: Buckminsterfullerene aggregates (nC(60)) and fullerol. Environmental Toxicology and Chemistry 26, 976-979. Zhu Y, Zhao Q F, Li Y G, Cai X Q and Li W 2006b The interaction and toxicity of multi-walled carbon nanotubes with Stylonychia mytilus. Journal of Nanoscience and Nanotechnology 6, 1357-1364.
63 Nanoparticles and the environment (TA-2304/2007)
Statens forurensningstilsyn (SFT) Postboks 8100 Dep, 0032 Oslo Besøksadresse: Strømsveien 96
Telefon: 22 57 34 00 Telefaks: 22 67 67 06 E-post: [email protected] Internett: www.sft.no
Utførende institusjon Kontaktperson SFT ISBN-nummer Bioforsk Jord og Miljø Bård Nordbø 978-82-7655-540-0
Avdeling i SFT TA-nummer Tilsynsavdelingen 2304/2007
Oppdragstakers prosjektansvarlig År Sidetall SFTs kontraktnummer Erik J. Joner 2007 64 5007148
Utgiver Prosjektet er finansiert av SFT SFT
Forfatter(e) Erik J. Joner, Thomas Hartnik og Carl-Einar Amundsen Tittel – norsk Produserte nanopartiklers opptreden og giftighet i miljøet
Tittel - engelsk Environmental fate and ecotoxicity of engineered nanoparticles
Norsk sammendrag Denne rapporten er en gjennomgang av vitenskaplig litteratur som omhandler mulige negative miljøvirkninger av produserte nanopartikler. Den er ment som et dokument som skal danne grunnlag for Statens forurensningstilsyns arbeid med forvaltningsmessige problemstillinger i forhold til utslipp og spredning av produserte nanopartikler til miljøet, og et utgangspunkt for norske standpunkter i slike spørsmål når disse drøftes i internasjonale fora. English summary The present report is a review of scientific results on the potential negative impact of engineered nanoparticles on the environment. It is intended as a background document for the Norwegian Pollution Control Authority (Statens forurensningstilsyn) in their work with regulatory issues related to the release of engineered nanoparticles into the environment and a basis for Norwegian points of view when such questions are debated in international forums.
4 emneord 4 subject word Nanopartikler, miljøgifter, toksisitet, Nanoparticles, environmental pollutants, ecotoxicity, risiko risks
64
Statens forurensningstilsyn Postboks 8100 Dep, 0032 Oslo Besøksadresse: Strømsveien 96
Telefon: 22 57 34 00 Telefaks: 22 67 67 06 E-post: [email protected] www.sft.no
Statens forurensningstilsyn (SFT) ble opprettet i 1974 som et direktorat under miljøverndepartementet. SFT skal bidra til å skape en bærekraftig utvikling. Vi arbeider for at forurensning, skadelige produkter og avfall ikke skal føre til helseskade, gå ut over trivselen eller skade naturens evne til produksjon og selvfornyelse.
TA-2304/2007 ISBN 978-82-7655-540-0