See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/280945058 Transformations that affect fate, form and bioavailability of inorganic nanoparticles in aquatic sediments Article in Environmental Chemistry · August 2015 DOI: 10.1071/EN14273 CITATIONS READS 9 512 1 author: Richard Cross University of Exeter 2 PUBLICATIONS 11 CITATIONS SEE PROFILE All content following this page was uploaded by Richard Cross on 27 August 2015. The user has requested enhancement of the downloaded file. RESEARCH FRONT CSIRO PUBLISHING Environ. Chem. Review http://dx.doi.org/10.1071/EN14273 Transformations that affect fate, form and bioavailability of inorganic nanoparticles in aquatic sediments Richard Kynaston Cross,A,B Charles TylerA and Tamara S GallowayA AGeoffrey Pope Building, Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter, EX4 4QD, UK. BCorresponding author. Email: [email protected] Environmental context. Engineered nanomaterials are increasingly being used and their release to the aquatic environment poses potential risk. We review the research on transformations of engineered nanomaterial in the aquatic sediment environments, and consider the implications of their release. The key factors defining the fate of engineered nanomaterials in aqueous and sediment systems are identified. Abstract. Inorganic nanoparticles are at risk of release into the aquatic environment owing to their function, use and methods of disposal. Aquatic sediments are predicted to be a large potential sink for such engineered nanomaterial (ENM) emissions. On entering water bodies, ENMs undergo a range of transformations dependent on the physicochemical nature of the immediate environment, as they pass from the surface waters to sediments and into sediment-dwelling organisms. This review assesses the current state of research on transformations of metal-based ENMs in the aquatic environment, and considers the implications of these transformations for the fate and persistence of ENMs and their bioavailability to organisms within the benthos. We identify the following factors of key importance in the fate pathways of ENMs in aqueous systems: (1) extracellular polymeric substances, prevalent in many aquatic systems, create the potential for temporal fluxes of ENMs to the benthos, currently unaccounted for in predictive models. (2) Weak secondary deposition onto sediment grains may dominate sediment–ENM interactions for larger aggregates .500 nm, potentially granting dynamic long-term mobility of ENMs within sediments. (3) Sulfurisation, aggregation and reduction in the presence of humic acid is likely to limit the presence of dissolved ions from soluble ENMs within sediments. (4) Key benthic species are identified based on their ecosystem functionality and potential for ENM exposure. On the basis of these findings, we recommend future research areas which will support prospective risk assessment by enhancing our knowledge of the transformations ENMs undergo and the likely effects these will have. Received 18 December 2014, accepted 6 May 2015, published online 14 August 2015 Introduction Attempts have been made to model the release of ENMs The use and application of engineered nanomaterials (ENM) is into the environment at both national and global scales[13–15]; rapidly expanding, with a global industry estimated to be worth however, a lack of data on production[16] and emission rates US$3 trillion by 2020.[1] This growth is reflective of their wide- inhibits accurate prediction of the release potential of ENMs.[17] ranging applications, spanning environmental remediation,[2,3] Recent estimates predicted 1100–29 200 Mg of the global ENM commercial products[4–7] and medicine.[8] The expansion of production in 2010 was released directly into water bodies[18]. commercial uses for ENMs is fuelled by the unique properties Most of these ENMs will pass through some form of water- materials display at the nanoscale compared with the larger treatment process before entering the aquatic environment, (bulk) form of the material, principally due to their high surface which can be highly effective at removing ENMs such as silver area-to-volume ratio.[9] It is this high reactivity at the nanoscale (AgNPs).[19] In one study, silver in the effluent from a model that has established ENMs as a contaminant separate from their waste-water treatment plant accounted for only 2.5 % of the bulk form. The commonly used definition of a nanomaterial is a original dosed concentration.[20] However, some ENMs may material with at least one dimension ,100 nm.[10,11] Nano- also be released directly to aquatic systems. Coatings and particles (NP) have all three dimensions ,100 nm, whereas cosmetics comprise the largest share of commercial products nanosheets and nanorods exist with one or two dimensions containing ENMs[21] and are the two largest potential sources of ,100 nm. In terms of regulation, the European Commission has ENM release into the environment.[18] Most ENMs utilised in a working definition of engineered nanomaterials as ‘containing coatings and cosmetics are inorganic metal or metal oxide NPs [22,23] particles, in an unbound state or as an aggregate or as an (MeO) such as titanium dioxide (TiO2), zinc oxide (ZnO), agglomerate and where, for 50 % or more of the particles in the silicon dioxide (SiO2) and cerium oxide (CeO2), which have number size distribution, one or more external dimensions is in high production and release volumes.[14,16,18] These may be the size range 1–100 nm’.[12] released from painted exterior facades and other consumer Journal compilation Ó CSIRO 2015A www.publish.csiro.au/journals/env R. K. Cross et al. products directly into the aquatic environment[23,24] with uncer- cellular internalisation may be physically or temporally con- tain ecological consequences.[25] There is little regulation in strained, whereas bioavailable ENMs may be readily interna- place for their production or disposal, making the area of nano- lised by cells and tissues. As such, transformations of ENMs ecotoxicology one of vital importance for prospective risk and their effect on bioavailability in sediments are an important assessment.[25–27] component of ENM hazard prediction. There has been recent Water bodies receiving ENMs present a diverse range of progress in standardising approaches to measuring the toxicity environments, from fast-flowing rivers to lakes high in natural of chemicals in sediment environments,[36] but the existing organic matter (NOM) or oceans of high ionic strength. Differ- framework for chemical contaminants may not be suitable for ences in both physical and chemical conditions of the immediate ENMs owing to the fundamental differences between solute environment may drastically alter the fate and behaviour of and colloidal chemistry. International efforts are working ENMs. Both naturally occurring NPs[28,29] and ENMs[30,31] towards achieving the same quality of standardisation and have been shown to aggregate and sediment on transport into environmental realism for nano as for traditional chemical saline environments as occurs when entering estuarine waters. ecotoxicology.[25,37,38] To do this, a firm understanding of the In the Gironde estuary, France, silver from anthropogenic transformations that occur through the products’ lifecycle is sources contributes 24–90 % of particulate Ag fluxes into of utmost importance.[39] [32,33] sediments. In some instances, for example TiO2 in the The present review critically analyses knowledge concerning Rhine river, modelled sediment concentrations exceed that in the hazard potential of inorganic ENMs in the benthic environ- the overlying water by up to six orders of magnitude.[34] ENMs ment. We distinguish between organic and inorganic ENMs have also been observed to move in run-off from terrestrial soil for the purposes of the current review owing to unique fate into aquatic sediments.[35] Therefore, sediments are predicted as processes of inorganic ENMs concerning dissolution and the a major sink for ENM emissions.[11] presence of ions, and the differences in the specific challenges The transformations that an ENM may experience on enter- for investigators that organic and inorganic ENMs present, ing the aquatic and benthic environment can be subdivided into which must be dealt with separately. The reviews focus is on four main categories: the interactions that occur between inorganic ENMs with both biotic and abiotic components of the benthic environment and Physical transformations, including aggregation processes the implications of these transformations for the fate and and deposition onto sediment grains. bioavailability of ENMs to benthic species. Investigating these Chemical transformations, including dissolution, exchange of processes and transformations will help identify the form of surfactants, influence of other inorganic chemicals and redox inorganic ENMs likely to be present within the benthos. In doing reactions. so, this information can be used in support of standardised Interactions with macromolecules external to organisms such testing for predictive risk assessment of ENMs in sediments. as NOM and extra-cellular polymeric substances produced in the water column or by biofilms at sediment surfaces. Biologically mediated transformations involving partitioning Transformations in the water column among benthic communities, bioturbation and transforma- Many transformations occur in the water