Biophysical Environmental Chemistry and the Other Environmental Disciplines Within Tion of Data Be Possible

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Chimia 49 (/995) 102-109 scribing in detail the primary to quater- © Neue Schweizerische Chemische Gesellschaft nary structures of proteins, polysaccha- /SSN 0009-4293 rides or DNA, and of even more complicated structures like biological membranes, even though such achievements were con- Biophysical Environmental sidered as impossible at the beginning of the century. Thus, undoubtedly, environ- Chemistry: A New Frontier for mental chemistry will succeed in describ- ing the components and structures that Chemistry play key roles in environmental processes. However, to achieve this as much time and effort as have been put in other disciplines Jacques Buffle*, Montserrat Filella, and Jingwu Zhang will be required and new sophisticated technologies and concepts should be developed. In particular, it is crucial to real- Abstract. The paper discusses the position and role of environmental chemistry among ize that environmental chemistry (like bi- the other environmental disciplines. It discusses the various aspects of environmental ochemistry) is more than just an applica- chemistry and emphasizes the need for developing fundamental studies in biophysical tion of 'classical' chemistry concepts and environmental chemistry in order to better understand the functioning ofenvironmental methods. Most of the latter have been systems. These systems include a large number of various structures in the nanometer developed for chemical systems composed to meter range which play key roles on compound fluxes and consequently on the of small molecules, often with only few homeostasis of ecosystems and on their disturbance by anthropogenic activities. Both components. Similarly, most analytical structures and fluxes are presently ill-known and new concepts and methods must be techniques have been developed for ho- developed in this field. For chemistry, this is a challenging area where supramolecular mogeneous systems, so that, physically structures and processes play dominant roles. It is also a challenging field for the complicated systems should initially be development of environmental sciences since detailed and sound physico-chemical transformed (by preliminary steps such as processes are needed in macroscopic modeling of compound circulation in ecosystems. filtration, dissolution of solid phases or In addition, teaching this discipline to chemistry students would allow them to confront extraction) into well homogenized sys- complex, structured real systems. This paper also discusses the relationship between tems in order that meaningful interpreta- biophysical environmental chemistry and the other environmental disciplines within tion of data be possible. Although such a integrated multidisciplinary studies. The structure used at the Faculty of Sciences of the 'classical' chemical approach has been University of Geneva to favour a flexible but efficient integration is briefly described. and is still useful in environmental sciences, it is not sufficient to understand the chemical basis of environmental system 'If you ask a chemist to find for you what biochemistry have passed through long functioning which largely depends on a dynamo is, the first thing he would do is descriptive periods in which important physico-chemical processes based on the to dissolve it in hydrochloric acid' (ALbert discoveries allowed deducing structures existence of biological and physical struc- Szent-Gyorgyi, 1893-1986; biochemist, and properties of elements and compounds. tures and of corresponding concentration Nobel price of Medicine 1937). This led to quantitative formulation of gradients and fluxes of compounds. This modem concepts allowing predictions to is again exemplified by means of the anal- be made on compound reactivity. Where- ogy with biological systems: the chemical 1. Introduction as descriptive phase in chemistry has prob- analysis of a homogenized biological cell ably reached its pinnacle, in biochemistry gives some information on its composi- Not all scientific disciplines have still a great deal has to be done. This lag is tion, but little on its functioning. reached the same stage in their develop- due to the greater complexity of the sys- The main goal of this paper is to em- ment. Today, environmental chemistry, as tem studied and, particularly, to the key phasize this particular aspect of environ- rational discipline, parallels the emergence role played by supramolecular organized mental chemistry which may be less fami- of biochemistry (formerly called biologi- structures. liar to the reader and which is called here- cal chemistry) in the first half of the present Environmental chemistry deals with after 'Biophysical Environmental Chemis- century. Achievement of scientific knowl- even more complicated systems than bio- try' to suggest the important role of su- edge includes several steps: formulation chemistry and it is a much younger disci- pramolecular physico-chemical structures of concepts, collection, classification, and pline. Therefore, despite the development and their links with biological activity. interpretation of data, and generalization of modem sophisticated analytical tech- We believe that this aspect of environ- and formulation of new more rigorous and niques, it is still at its infancy, i.e. much mental chemistry should be significantly quantitative concepts. Both chemistry and work has still to be done on experimental more developed to allow ultimately effi- data collection and classification. Let us cientenvironmental protection. To clearly think for instance about sediments, soil point out the peculiar features of this as- *Correspondence: Prof. J. Buffle aggregates or humic compounds which pect of environmental chemistry, we com- Groupe de Chimie Analytique et Biophysico- are key environmental components but pare it with 'classical' environmental chimique de l'Environnement (CAB E) whose rigorous chemical description is chemistry based on the application of well- Departement de Chimie Minerale, extremely difficult. This enormous diffi- established general chemistry and chemi- Analytique et Appliquee Universite de Geneve culty does not mean that rigorous descrip- cal analysis concepts to environmental Quai Ernest Ansermet 30 tion of environmental systems is impossi- systems. The term 'classical' chemistry is CH-121] Geneve 4 ble: biochemistry has succeeded in de- used here for the sake of clarity to distin- UMWELTSCHUTZ 103

CHIMIA 49 (1995) Nr. 4 (April) guish it from 'biophysical' chemistry. This comparison should help to understand the .- Environmental microbiology - role of environmental chemistry amongst --- Geochemistry, ecology, hydrogeology ~ the other environmental sciences as well Environmental chemistry as one of the chemical disciplines, which Spatial may bring new challenges to the develop- scale ment of chemistry. We will discuss here • co Mathematical mostly this latter aspect and put 'classical' c CI) :CE modelling chemistry and biophysical environmental c _CI)tIl- chemistry in perspective with one another. CI):>' <1>_-CI) "0 til r::- Molecular + microscopic Macroscopic + global ",c iiiE processes 1 processes 2 2. The Place of Environmental 13eE'- til 1; Chemistry in Environmental Sciences "0<1> c_ ~ Environmental ~ ~o analytical chemistry 4 A simplified but useful representation discriminates between three aspects of all co til c- environmental natural sciences (Fig. 1): .-"0='" """'------_/ ~~{co , the fundamental understanding of the func- ,!!lo. ~o Anthropogenic effects tioning of unperturbed environmental sys- "0<1><1>_ co on environment 3 tems (boxes 1 and 2), and the understand- ;:)- ing of anthropogenic perturbations on these systems (box 3).lt is essential to make the Fig. 1. Different aspects covered by environmental natural sciences distinction between aspects 1 and 2 on the one hand and 3 on the other: anthropogen- far the most widely used. In particular, ing (box 3). Obviously, since chemistry ic perturbations cannot be understood and such approaches are the ones applied to influences many geological and biologi- controlled without a preliminary under- quality monitoring in governmental insti- cal processes, these methods are required standing of the behavior of unperturbed tutions. As mentioned above, they have not only by chemists but also by most ecosystems (see below the analogy with their usefulness but environmental chem- other environmental scientists. Analytical medicine, Fig. 2). A major role of environ- istry should not be restricted to this classi- chemistry has thus a key role to play in mental chemistry, therefore, is to study the cal approach, as it is not sufficient to almost all aspects of Fig. 1.Because of it, physico-chemical processes occurring in provide the necessary concepts and infor- a common idea is that the development of unperturbed environmental systems. mation for developing predictive models analytical methods for environmental qual- It is also useful to discriminate be- of ecosystem functioning. Complementa- ity control is the major role of environ- tween environmental 'microprocesses' ry studies on molecular and microscopic mental chemistry. This notion is not cor- (occurring at small scales: nm to mm; box structures and related processes (box 1), rect, as itcan be understood by the analogy I) and 'macroprocesses' (large scales: mm i.e. biophysical environmental chemistry, between environmental and medical sci- to km; box 2) corresponding to whole are required. They need long-term physi- ences discussed below (Fig. 2): ecosystems. Fig. 1 shows that in both co-chemical investigations, with sophisti- - Although, unquestionably, environ- cases their study should be done in close cated techniques and high-level biophys- mental analytical chemistry is of great association with microbiology and geo- ical, biochemical or physico-chemical importance to all environmental scien- chemistry. Although the border between competence which are generally only avail- tists, environmental chemistry should these two scale ranges is rather arbitrary, able in chemistry and biochemistry de- not be confined to it. The study of the nature of the corresponding processes, partments. Therefore, full development of biophysico-chemical processes is an- the techniques used to study them and, environmental chemistry should include other key component of environmen- consequently, the corresponding concep- the biophysico-chemical approach as well tal chemistry, as important for the ulti- tual approaches are very different. Tradi- as the aforementioned classical aspects. mate protection of environmental tionally, in many universities, environ- Both branches should be in close contact health as biochemistry and biophysics mental chemistry has been developed in with non-chemical environmental disci- are for medicine. Incidentally, the anal- non-chemistry departments (department plines. But, while the classical approach ogy with medical sciences also hel ps to of soil science or agriculture for soil chem- can be developed in non-chemical depart- understand the difference between istry, of oceanography for chemical ocea- ments since it is based on well-established 'classical' and biophysical environ- nography, of meteorology for atmospher- concepts and methods, the biophysico- mental chemistry: they parallel physi- ic chemistry, of civil engineering or geol- chemical approach should be studied and ology, and biochemistry or biophysics ogy for geochemistry or groundwater developed in chemistry or biochemistry respectively. At any rate, the simulta- chemistry, etc.). Consequently, the devel- departments and requires its recognition neous development of anal ytical chem- opment of environmental chemistry has by the other chemical disciplines as an istry and process studies is as vital for been largely driven by non-chemical dis- important branch of applied chemistry, solving environmental chemistry prob- ciplines interested in macroscopic as- equivalent to biochemistry. lems as for combating diseases in the pects of environmental sciences (box 2), Another major task of environmental medical domain. and hence 'classical' chemistry concepts, chemistry is to develop the analytical - The nature of environmental analyti- valid for well-mixed systems, as well as chemical methods (box 4) needed to study cal chemistry itself should be discussed. 'classical' analysis applicable to homoge- environmental processes (boxes 1 and 2) Because environmental chemistry has nized samples, have been and are still by and allow environmental quality monitor- often grown in non-chemical universi- UMWELTSCHUTZ 104 CHIM1A 49 (1995) NT.4 (April)

ty departments, environmental analyt- to undertake fundamental studies in phate through biological membranes, ox- ical chemistry has been largely restrict- this field, thus hampering environmen- idation of organophosphorous compounds, ed to the application of classical ana- tal science to develop into a sound phosphate adsorption on iron hydroxide, lytical methods to environmental sam- science. This may have dramatic con- nucleation of iron phosphate, oxidation of ples. Even though quite sophisticated sequences for the future generations, Fell into FellI, calcium phosphate crystal and very useful adaptations of instru- which will be confronted to more seri- formation, growth and dissolution which mental analytical techniques have been ous pollution problems than ours, but itself may depend on adsorption of surface done, original analytical concepts or who will have no rigorous scientific active organic compounds, etc. Each of approaches (Sect. 3.2) are only rarely discipline to solve them. these steps is intricately related to other developed specifically for studying en- Sect. 3 gives more details on the type of physico-chemical processes, in a manner vironmental processes. In fact, such fundamental biophysico-chemistry stud- analogous to the metabolic cycles in bio- developments require i) long term in- ies and advanced analytical chemistry de- chemistry (e.g. Krebs cycle for glucide vestigations, and ii) tight coupling with velopments which are needed. metabolism in organisms). The primary detailed physico-chemical process role of biophysical environmental chem- studies which are outside the scope of istry is to elucidate the most important most non-chemistry departments. 3. Specificity of Biophysical steps at the molecular and microscopic - Because of the urgency of solving pol- Environmental Chemistry as a level, in particular, those which playa rate lution problems, most administrations Chemical Discipline limiting role in the overall cycle of the and many research foundations favor element of interest. The aforementioned the founding of strategic short-term 3.1. Study of Environmental microprocesses are examples of processes and, therefore, empirical studies. Be- Biophysico-Chemical Processes which are rarely studied in detail in mac- cause of the key role that environmen- As far as physico-chemical processes roscopic non-chemical disciplines, as tal chemists have to play in developing are concerned, work conducted over the pointed out in Sect. 2, and that would be analytical methods for environmental last 20-30 years by Stumm [2][3], Schin- more easily tackled in chemistry or bio- quality monitoring, they are under a dler [4] and others have clearly shown that chemistry departments. Only then would strong pressure to move progressively global geochemical cycles of elements are it be possible to model rigorously the from fundamental studies onto bio- ultimately controlled by the reactivity and corresponding physico-chemical process- physico-chemical processes to tackle physico-chemical properties of compounds es to include them as submodels in global short-term problems related to envi- at the molecular level and that, without a models of ecosystem functioning. Pres- ronmental management. A real danger good knowledge of the behavior of chem- ently, most global models include physi- lies here for the future. Urgent pollu- ical compounds at this level, no prediction cal, biological, or geochemical macro- tion problems must be solved without will be possible at the global level [25]. processes, but they rarely include detailed any doubt, but one should not forget The cycling of phosphorous in lakes (with microprocesses, because of the dearth of that for the long-term basic research is possible concomitant lake eutrophication) available data. As a result, global models the most useful and it pays off [1]. is an interesting example of an old impor- often fail to represent adequately detailed Without the results oflong term funda- tant problem, which has been studied for spatial distribution or seasonal evolution mental studies in biochemistry and decades, without yet being able to find ofchemicalcompounds [5][25]. Converse- microbiology, it would not be possible models giving satisfactory quantitative ly, in cases where such detailed studies of to fight against tuberculosis, diabetes, description of the complete cycle [5]. This physico-chemical, and/or microbial proc- cancer and many other diseases today. is because phosphorous cycling (as that of esses have been made, good concordance By favoring short term empirical stud- most chemical compounds) depends on between experimental and predictive cal- ies on the environment, the authorities many still largely ill-known physico-chem- culations are obtained, such as that for the discourage thorough-minded scientists ical mechanisms such as transfer of phos- fate of herbicides in the Rhine River after Schweizerhalle accident [6]. In contrast to the usual systems studied in chemistry, environmental chemistry systems have the striking feature that many «l of their properties are closely related to c: Biochemistry Biophysical -(I) their physical and chemical heterogenei- E Biophysics environmental chemistry «l ty. The study of environmental physico- "0 c: chemical processes, therefore, requires us- ;:, U. ~ ~ ing new conceptual approaches combin- Medical Environmental analysis ing classical chemistry concepts with ad- analysis (Monitoring) ditional ones, in particular reactivity probability concepts and supramolecularstruc- tural physical models. The main features ! ! characteristic of biophysical environmen- Health Environ mental tal chemistry are described below. control management a) The chemical heterogeneity of environmental systems is a first major difficulty for non-environmental chem- HUMAN HEALTH ENVIRONMENTAL HEALTH ists who are usually trained to think in terms of reactivity of individual, small Fig. 2. Analogy between environmental and medical sciences molecules. According to this approach, UMWELTSCHUTZ 105

CHIMIA 49 (1995) Nr. 4 (April)

b) .-.... •....) c) -,. OH .....W·'-·· ', .:.:\.).• ·.:.v•...•. ~. _:0, "• '-....1/,.,oH "I ,/"OH .~ ....•...... ;"~...... •...,. Ho~le"OH~Fi~OH : ":':'" ....•'..... '. ..~'''. fA :. HO...... ••.I /OH HO~ I/" ....•.f.:,~-:,~. •• .•...... ~~. /Fi'lOH Hor'j'---OH .. ." .. ••... l,;;, ..•.• HO"" I /OH" , /OH ' . Fe Fe .:.:. ') . ,...... HO,./" I-...... OH~I""-... .~...... HO 200 nm -

Fig. 3. a) Iron hydroxo-phosphate globules (spherical black particles with size < 0.2 1lJU)formed at the oxic-anoxic boundary layer of a eutrophic lake (Hret, YD, CH) [15]. These globules are aggregated with other colloidal material, filaments, and bacteria (not visible in this figure), which influence the sedimentation rate and bioavailability of iron and phosphate. b) Kinetics of aggregation between spherical colloids and comparatively larger filamellts or macromolecules can be simulated by numerical modelling. c) Cyclic hexanuclear precursor which has been shown to beformed in laboratory during the oxidation of Fell at neutral pH [16]. The iron globules of Fig. 3a have well-defined chemical composition, and transmission electron microscopy shows that they are themselves aggregates of small units (1-2 nm in size), possibly the precursor shown in Fig, 3c.

the study of a complex mixture con- the properties of individual molecules sediments or dust particles in the low sists of a first detailed characterization by introducing the concept of reaction troposphere are examples of micro- of each component of the mixture. The probability [9-11]. Description of such structures in the range nm to mm (Fig. complexity of environmental systems, chemical systems should then be based 3). They playa key role for example for however, is huge and complete charac- on rigorous statistical concepts, appli- the circulation of oxygen and water in terization is never possible. Even if cable not only to a large number of soils and for that of most nutrients in one casts aside the enormous efforts identical molecules (as usually done in the whole biosphere, and, therefore, required to study environmental prob- classical thermodynamics), but also to they exert key influences on the main- lems in this manner, the solutions to a system consisting of a large number tenance of life. Sediment-water inter- the questions posed are not always of similar but nevertheless not identi- faces in lakes and oceans are other obtained. Indeed, this approach ignores cal molecules. Similar approaches are example. They are stratified at the ~n that heterogeneity by itself is a key applicable to some of the chemical to mm level (Fig. 4) in sllccessive property of the environmental systems properties of whole soils and sediments. layers of varying chemical composi- of interest. Fulvic and humic com- b) It is now well established that the most tion, which controls the overall ex- pounds of soil and waters provide a important reactions in environmental changes of chemicals between the bulk good example of such a case. Even systems (soil, sediment, oce,an, fog water and the sediment. Similarly, the after 'purification', fulvic and humic droplet) occur in solid-liquid and gas- gas exchanges at the ocean/atmosphere

samples are composed of a large liquid inteifaces [3][12-14]. Theelec- interface (such as that of CO2 with its number of similar but not identical tric field and solvent structure are very link to climate change) are predomi- compounds. As an ensemble, they act different at these interfaces (over a nantly controlled by a diffusion layer cooperatively as a complexing system thickness of tens of nm) than in the of 30-80 f..U1l thickness whose chemi- for metal ions (and small organic mol- bulk solution and thus may drastically cal composition is very different from ecules), with significant buffering in- modify the nature and rates of chemi- the bulk solution. In all cases, the func- tensities spanning over an extremely cal reactions. Unfortunately, a fast tioningoflivingenvironmental macro, wide concentration range of metal ion. glimpse at many chemistry curricula and microsystems is very much de- As such they playa key role in main- for chemistry students shows that sur- pendent on their physico-chemical taining acceptable concentrations of face reactions (adsorption isotherm, structure (see d); indeed the function- vital and toxic metal ions for organ- interface catalysis, etc.) are barely ing of living systems (organisms or isms in soils and waters [7-9]. Alone, (sometimes not at all) taught. ecosystems) is based on pH, redox and none of the individual molecules will c) The previously mentioned interfaces other chemical gradients which can impart this property. Hence, they should are the simplest examples of environ- only develop with physical heteroge- be thought of as a single chemical mental microstructures. All environ- neity [15][18]. A good characteriza- system rather than as a mixture of mental systems are physically struc- tion of environmental microstructures individual compounds. This buffering tured at all levels, from nm to km is, therefore, a key task of environmen- action due to chemical diversity (or range. Examples oflarge structures are tal chemists (as characterization of cell chemical heterogeneity) can be seen as soil horizons; lake, ocean or atmos- structure is a key aspect in biochemis- equivalent to the increased stability of phere stratification; geological layers. try). This implies knowledge in colloid ecological niches when the number of Microstructures are those which envi- chemistry, macromolecular physico- biological species increase (biodiver- ronmental chemistry is more concerned chemistry and biophysical concepts as sity). It has been shown that the overall with. Aggregates between large poly- well as the development of adequate properties of heterogeneous chemical saccharide macromolecules, clays and analytical tools. These fields are also systems may be rigorously related to microorganisms in soils, water, and rarely included in the usual training of UMWELTSCHUTZ 106

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chemists which is largely focused on students. Not only the coupling of 3.2. Environmental Analytical homogeneous solution chemistry (see chemical and diffusion equations is Chemistry introductory quotation by Szent-Gyor- rarely taught, but often more emphasis Anal ytical chemistry, i.e. development gyi). is laid on chemical equilibria than on of new analytical methods based on new d) The physical structures existing at all chemical kinetics. The coupling of physico-chemical principles, is a well- scales of environmental systems and chemical reactions with hydrodynam- established branch of chemistry and will the corresponding chemical gradients ic transport processes is also not taught not be discussed here. However, environ- imply the existence of fluxes of com- to university chemistry students. With mental sciences definitely need the devel- pounds within the system of interest respect to that particular aspect, chem- opment of new analytical methods specif- (e.g. soil aggregate), or between one ical engineers may have a better train- ically adapted to the physico-chemical compartment and the neighboring one ing to solve macroscopic environmen- nature and properties of the environmen- (sediment-water interface). Environ- tal chemical problems. tal systems under study. Many pollutants mental systems (micro- and macrosys- It is essential to realize that properties or vital compounds in environmental systems) are, therefore, dynamic ones. related to items a to d above, in combina- tems are present at trace levels. Concen- Understanding environmental process- tion with classical chemical reactions, are tration levels below the ppb are currently es then necessarily implies coupling key factors for the maintenance of the determined. High sensitivity combined to kinetics of chemical reactions with homeostasis of environmental systems. large selectivity (due to the complexity of physical transport processes [18][ 19]. They also correspond to processes of en- environmental systems) are, therefore, key This often occurs by molecular diffu- vironmental systems which are particular- characteristics of environmentally useful sion in microsystems (e.g. soil or un- ly sensitive to impacts of anthropogenic analytical methods. This also implies much derground pore water), as well as by activities. These concepts should then be precaution to avoid contaminations and eddy (turbulent) diffusion and laminar taught in detail to future environmental losses by adsorption on vessels. Much or turbulent hydrodynamic flow, at the scientists, and even given at a general work has been done to solve these prob- macroscopic level (e.g. lakes, rivers, level to chemistry students, so that they lems for environmental applications, by atmosphere). This is an additional la- could take them into account during their combining careful sampling and sample cuna in the training of most chemistry professional life. handling to sometimes very sophisticated instrumental techniques, such as ICP-MS, GC-MS, HPLC-MS, Flow Field Flow Fractionation techniques, NMR and FTIR, or Surface analysis techniques (e.g. Parti- cle Induced X-Ray Emission, Laser Mi- croprobe Mass Spectrometry, X-Ray Flu- orescence or Electron Energy Loss Spec- troscopy, etc.). Such analytical developments are extremely helpful for the progress of environmental sciences. In most cases, however, the sample structure is destroyed and/or average analysis is done. Such analysis cannot give any information on the links between chemical composition or properties and sample structure. These analytical developments hence are similar to those made for non environmental fields, and belong to 'classical' analytical chemistry, according to the distinction made in this paper. As discussed in Sect. 3.1, what is more specific to en vironment is that ecosystems are dynamic and physically nonhomoge- neous. Monitoring average concentrations of compounds is then not sufficient for quality control; concentration gradients which occur over distances sometimes smaller than mm are also key parameters -100 Ilm for making predictions on chemical fluxes within or between environmental com- Fig. 4. Fine chemical stratification at the top sediment of sediment-water interface in an anoxic lake. partments. This implies developing new The two layers correspond, from top to bottom, to manganese oxide, and iron oxide formed in situ on specific methods enabling to perform in Teflon plates inserted vertically in the sediment [17]. Picture is obtained by electron microscopy situ, remote sensing of these fluxes, with- coupled to mapping by energy dispersion spectroscopy. Each sediment layer is a few nun thick and out perturbing environmental systems ei- the separation zone between the two layers is LOO/lI11 reflecting very steep vertical redox gradients in ther by chemical contamination or by phys- the sediment. Transmission electron microscopy shows that the iron oxide layer is composed of either amorphous iron hydroxide globules (similar to those of Fig. 3a) or crystallized lepidocrocite, ical disturbance. This will also allow con- depending on lake pH (neutral or acid, respectively). The exact nature of these layers influences tinuous monitoring of chemical parame- phosphate and many other trace compound fluxes between water and sediments. ters, in real time, which is required for UMWELTSCHUTZ 107

CHIMIA 4Y (1995) Nr. 4 (April) efficient pollution control. The development of such systems became recently feasible, thanks to new technological ad- vances. For instance devices have been CHEMISTRY built which allow to determine oxygen, anions or trace metal concentration pro- files (e.g. [20]) at the sediment-water interface, while keeping a resolution of 100 CABE llJ11, i.e. that corresponding to the strata thicknesses on the top sedi ment layer (Fig. m BIOLOGY ::> CENTRE OF S 4). Another example is the development of < c ENVIRONMENTAL •• R "" a E ::> EARTH NOx sensors with very fast response time ca ::> c .., 3 NATURAL SCIENCES 0 HUMAN co e g, SCIENCES (fraction of second) for recording fluctua- ••::> ";; BIOLOGY (CESNE) c tions of NOx concentrations in the low ~ w troposphere. Such fluctuations are direct- Fig. 5. Links het\l'een ly linked to eddy diffusion processes, and the various experi- Envlronmentel provide more precise estimates of NOx mental groups of the groups fluxes than gradients based on classical Faculty of Sciences concentration profile measurements. at the Universi(\' of Geneva, their hasic Another specific aspect of environ- PHYSICS Departments (Sec- mental analytical chemistry is related to AND ASTRONOMY tions) and the Fac- speciation [7]. Bioavailability, and conse- ulry Centre of Natu- quently, toxicity of any particular element ral Environmental or compound for a microorganism de- Sciences (CESNE) pends both on its flux inside the microec- osystem surrounding the organism and on its chemical form (so-called chemical spe- interfere with most sensors. They can be concepts for solving macroscopic en- cies, e.g. redox state, complexation with easily separated by filtration in laboratory vironmental problems, by knitting natural ligands, etc.) [21]. Presently, most but this procedure is not applicable at closely with other scientific disciplines, of the threshold limits oftoxic compounds depths of several 100 m in lakes oroceans: in a fully integrated manner. are fixed by rather arbitrary governmental obviously new analytical concepts and The second type corresponds to 'bio- regulations, imposing generally a maxi- methods have to be developed for in situ physical environmental chemistry' and mum tolerable average total concentra- remote analytical methods. Such develop- advanced environmental analytical tion of the compound in the ecosystem of ments require that analytical developments chemistry as discussed in Sect. 3. It interest (soil, water, etc.). Chemical speci- be done in close cooperation with bio- should be dealt with in biochemistry or ation in particular is often not considered physico-chemical studies and that analyt- chemistry departments, by specialists because of the lack of data or adequate ical chemists go to work on the field, with in biophysical, physico-chemical or bi- analytical technique. Development of non- real systems, under natural conditions, in ochemical processes, trained to apply perturbing speciation analytical methods close cooperation with environmental sci- these concepts and methods, and de- coupled to detailed biophysico-chemical entists, micromechanic and electronic en- velop new ones, to environmental sys- environmental studies are, therefore, a pre- gineers to consider the constraints of in tems. Eventually, these latter will be- requisite for building sound ecotoxicolog- situ measurements. This makes environ- come the concepts and methods used ical regulations. mental analytical chemistry a challenging in the above 'classical' approach. This Such analytical developments are a multidisciplinary science. discipline, therefore, is very important basic requirement if we wish to solve also for the improvement of environ- future environmental problems. But it is mental monitoring and management. also a big challenge. It is becoming feasi- 4. Teaching and Research in Although enough interactions should ble thanks to the fast progresses of nano- Environmental Chemistry exist between this discipline and other and microtechnologies and their applica- environmental sciences for ensuring tion to the development of remote control- 4.1. The Position of Environmental the study of environmentally relevant led microsensors and integrated micro- Chemistry in a Faculty of Sciences problems, integration with other disci- analytical systems [22]. It should be real- From the above discussion, in particu- plines may be less stringent than for ized, however, that laboratory develop- larSect. 2, it appears that, both for research 'classical' environmental chemistry. ment of such systems by analytical chem- and teaching, there is a need for two types Classical environmental chemistry can ists (as good as they can be) will not be of environmental chemistry (without clear- be taught at various levels, as one type of successfully applicable in the field unless cut boundary between them): applied chemistry to chemistry or non- an important research effort is also done to - The first type has been called here chemistry students interested in general transform the sensors operative in labora- 'classical' environmental chemistry, environmental sciences, with a view to tory conditions, into probes working rou- including 'classical' environmental an- work ultimately on multidisciplinary stud- tinely and reliably in situ. This requires alytical chemistry. It may be incorpo- ies of anthropogenic impacts. Biophysical developments which may be at least as rated in non-chemistry departments. environmental chemistry should be spe- difficult as the sensor development itself. Its role is not to form front-line chem- cifically taught to chemistry and biochem- Let us just think for instance of the sus- ical research but to apply modern istry students. We believe that such teach- pended particles of water samples which though well-established methods and ing is of vital importance for environ men- UMWELTSCHUTZ 108

CHIMIA 49 (1995) Nr. 4 (April) tal chemistry (and environmental protec- These considerations apply to all disci- lar macroscopic process. However, tion), and is also a key training for chem- plines. But, as a learning mean, modelling results of in situ measurements cannot istry students since this is one of the few is particularly important in environmental provide precise values of physico- opportunities they have to confront com- chemistry: it is the only too] available to chemica] parameters. These can only plicated structured systems in the rest of quickly evaluate the indirect but some- be determined in the ]aboratory, by their curriculum. times predominant influence, on the mac- using model experimental systems that Various types of organization may be roscopic evolution of ecosystems, of fac- mimic natura] ones. The combination imagined to solve the dilemma of environ- tors which affect molecular or microscop- of these two complementary approach- mental chemistry which should be inte- ic processes [25]. Lets take again lake es is essential to build environmental grated both in a multidisciplinary institu- eutrophication as an example: it depends chemistry as a rigorous discipline. tion as far as 'classical' environmental on a number of molecular or microscopic - Deve]opment in the laboratory and chemistry is concerned, and into chemis- processes such as formation rate of iron application in situ of analytical meth- try departments for biophysical environ- hydroxide species like that shown in Fig. ods specifically designed for studying mental chemistry. At the Faculty of Sci- 3, its reactivity with phosphate ions, its environmental processes. Measuring ences of University of Geneva (Fig. 5), the aggregation processes to form microscop- the right parameters in correct condi- environmental group of each scientific ic globules and more complicated aggre- tions is a key issue in order to under- discipline (environmental chemistry, en- gates (Fig. 3), and its sedimentation. Al- stand natural processes. This is far to vironmental biology, etc.) belongs to the though each step must be studied experi- be trivia] in complicated and struc- department (Section in Geneva University mentally, only mathematical simulation tured natural systems, and often signif- language) of its individual discipline combining microscopic and macroscopic icantly more complicated than with (Chemistry, Biology, etc.) and to a larger processes allows understanding the re- well controlled systems, in laboratory structure (CESNE = Centre of Natural spective role of each of them on the overall conditions. Environmental Sciences) directly attached evolution of the lake. In general, the time to the Faculty. This for instance allows and space domains of chemical processes 4.4. Teaching Environmental Chemistry CABE (group of Analytical and Biophys- are very far away from those occurring at Concepts ical Environmental Chemistry) to perform the macroscopic or global scale in envi- Sect. 3 discusses the basic physico- biophysical chemistry research and to teach ronmental systems (Fig. 6). It is thus ex- chemical concepts which are currently to chemistry students in the chemistry tremely difficult, both for students and missing in many curricula of chemistry department, while contributing by means researchers, to assess the actual impor- and are a prerequisite for understanding of 'classical' environmental chemistry to tance of chemical processes on ecosystem environmental chemical processes. The multidisciplinary studies and teaching in evolution. Modelling is an extremely use- teachers, in the classroom, will be faced the frame of CESNE and its Diploma in ful tool to do it (Fig. 1, box 5). It is also with two additional difficulties of a gener- Natural Environmental Sciences. This flex- helpful for non-chemists to learn the im- a] type, other than those specifically relat- ible structure is helpful not only to envi- portance of using detailed physico-chem- ed to the principles, while teaching these ronmental chemistry, but for the same ical processes instead of empiric a] param- concepts to the students. The first is relat- reasons, to all other environmental disci- eters to make reliable quantitative predic- ed to the time and space scales covered by plines. tions. environmental sciences (Fig. 6). It is not always easy to make the students to grasp 4.2. Role of Modelling 4.3. Experimental Work the idea as to how chemical processes In recent years, the use of numerical As mentioned earlier, expertise in any occurring at the ns to ms level can affect simulation models as a means to evaluate scientific discipline can only be acquired ecosystem evolutions over centuries or large-scale or complex natural processes by working experimentally in that field for even geological times and again, mode- has increased sharply. In some cases, the some period of time. This is even more ling is a very useful too] here. Another predictions generated by these models are important in environmental sciences be- problem is our 'sensitive' time window. considered as a basis for public policy cause of the complexity of environmental Everyone understands the meaning of decisions (e.g. global circulation models systems and the multidisciplinarity of the time flow, in the time range from fraction to predict Earth climate). There is an over- problems involved. As far as environmen- of second to millennia. This type of scales emphasis on the predictive value of mod- tal chemistry is concerned, the student are met in environmental macroprocesses elling. Even by neglecting the fact that all should be confronted at least with the (often biological, geological, physical models are oversimplified compared to following three experimental aspects: processes), where the student does not natural processes, many natural processes - Study of physico-chemical processes have problems visualizing it. However, are still unknown and, above all, the pri- in situ (in the field). Planning and per- the time-space windows in physico-chem- mary value of models is heuristic [23]. forming well-controlled experiments ical processes are very much different The prediction capability of models then in the field is much more difficult than from the above ones and it is difficult to should never be the main goal of model- in the laboratory, because of the large make the students visualize their relevance ling. On the other hand, it is unquestiona- number of factors to be considered and in environmental chemistry (i.e. the link ble that models have enormous impor- controlled in order to allow sound in- between chemistry and macroscopic envi- tance as educational tools both for stu- terpretation of data. ronmental processes). The situation be- dents and researchers. They allow in par- - Study of biophysico-chemical proc- comes worse if one compares the 'sensi- ticu]ar i) classification of information, ii) esses in the laboratory with model com- tive' space window of man (fraction of checking working hypothesis with exper- pounds simulating natura] systems. mm to tens of km) to the size of plankton imenta] data, iii) formulation of new hy- Studies on natura] systems allow to (10-5-10-4 m), colloidal particles pothesis by eliminating unimportant fac- discriminate between predominant and (10-8-10-6 m), or simple molecules (10-9 tors, and iv) sensitivity analysis. secondary factors affecting a particu- m). These entities differ in size by orders UMWELTSCHUTZ 109

CHIMIA 49 (1995) Nr. 4 (April) of magnitude, and, therefore, behave in a Measurable time Human liIe completely different manner. The impor- 1------+-1 tance of these differences is not obvious to the students confronted for the first time to Acid-base Chelate Bacteria Ocean's Age these concepts. reactions formation liIe span turnover of Earth A second difficulty of environmental chemistry is that many different concepts 1 s 1 Y 1 billion y I I I I I I I I I I I I I I I I I , I I I I I. have to be integrated to understand the -13 -11 -9 -7 -5 -3 -1 3 5 7 9 log(time) behavior of any particular environmental system. The principles of the various individual chemical reactions (acid-base, redox, complexation, precipitation, hydrol- CHEMISTRY BIOLOGY GEOLOGY ysis, etc.), that may occur in this system, are often easy to understand. It is, however, much more difficult for students to 1~m 1m decide which processes to ignore and which 1 1 I , , t I I t I I I I 1 I , 1 I 1 1 I" ones to consider, i.e. which ones playa -11 -9 -7 -5 -3 -1 3 5 7 9 log(distance) major role in the evolution of the environmental system of interest, in particular Ions Bacteria Man Globe when non-chemical processes have also to dimensions be taken into account. In most curricula of chemistry, students learn to understand Visible space of man V~al space of man single processes in depth, but they are not trained to combine many processes to- Fig. 6. Time and space domains covered by environmental sciences gether and even less many concepts of different disciplines. At the general teach- (which anyway is a major issue) is to give ronmental, Analytica] and Physical Chelll- ing level, this may be one of the most them the basic concepts necessary to learn istry Series, Lewis, Chelsea, iv!1,]992. important input of environmental chemis- and progress by themselves. []2] W. Stumm, 'Aquatic Surface Chemistry. try to chemistry students. Even if they do Chemical Processes at the Particle-Water Interface', Wiley, New York, 1987. not pursue their studies in environmental The authors wish to thank P. W. Schindler for [13] sciences, learning how to combine and his helpful comments. W. Stumm, 'Chemistry of the Solid-Water Interface. Processes at the Mineral-Water compare quantitatively many differentfac- and Particle-Water Interface in Natural tors affecting a given process, will be a Systems', Wiley, New York, 1992. very fruitful training for any real world Received: December 19, 1994 [14] P.W. Schindler, in 'Adsorption ofInorgan- applications. ics at Solid-Liquid Interfaces', Eds. M.A. [I] D.E. Koshland, Science 1993, 259, 291. Anderson and AJ. Rubin, Ann Arbor Pub., [2] W. Stumm, 1.1.Morgan, 'Aquatic Chemis- Ann Arbor, MI, 1981,Chapt. L 5. Conclusion try: An Introduction Emphasizing Chemi- [15] 1. Buftle, R. De Vitre, 'Chemical and Bio- cal Equilibria in Natural Waters', 2ndedn., logical Regulation of Aquatic Systems', Wiley, New York, 1981. Lewis, Chelsea, MI, 1994. The learning of a science in general [3] W. Stumm, 'Chemical Processes inLakes', [16] W. Schneider, B. Schwyn, in 'Aquatic Sur- involves more than the acquisition of new Wiley, New York, 1985. face Chemistry. Chemical Processes at the knowledge by a blank mind. Instead it [4] P.W. Schindler, in 'Circulation of Metals Particle-Water Interface', Ed. W. Stumm, involves a substantial restructuring of pre- in the Environment', 'Metal Ions in Bio- Wiley, New York, 1987,p. 167. existing knowledge, in which new knowl- logical Systems', Ed. H. Sigel, Marcel [] 7] N. Belzile, R.R. De Vitre, A. Tessier, No- edge must compete with the student's pre- Dekker, New York, 1984,Vol. 18, p. 223. ture (London) 1989,340, 376. [5] Y. Tyutyunov, R. Arditi, in ClPEL, 'Rap- [18] L.J. Thibodeaux, 'Chemodynamics', Wi- vious knowledge and familiar way of think - port de]a Commission Internationale pour ley, New York, ]979. ing [24]. This is particularly trueforchem- la Protection des Eaux du Leman', CIPEL, [19] R.P. Schwarzenbach, P.M. Gschwend, istry students learning environmental Lausanne, 1994, p. 243. D.M. Imboden, 'Environmental Organic chemistry and environmental sciences. [6] DJ. Mossman,J.L. Schnoor, W. Stumm,J. Chemistry', Wiley, New York, 1993. It should also be clearly stated to the Water Poll. Contr. Fed. 1988,60, 1805. [20] W. Davison, H. Zhang, Nature (London) students that any curriculum of one to [7] J. Buffle, 'Complexation Reactions in 1994,367,545. three years in environmental chemistry or AquaticSystems:anAnalyticalApproach', [21] A. Tessier, D. Turner, Eds., 'Metal Speci- Ellis Horwood, Chichester, 1988. ation and Bioavailability in Aquatic Sys- environmental sciences is insufficient to [8] J. Buffle, in 'Circulation of Metals in the terns'. IUPAC Environmental, Analytical make them specialists of environmental Environment', 'Metal Ions in Biological and Physical Chemistry Series, Wiley, processes. The basic requirement for a Systems', Ed. H. Sigel, Marcel Dekker, Chichester, 1995. medical degree is five years, and special- New York, ]984, Vol. 18,p. 165. [22] M.VaIcarce],M.D.LuquedeCastro,'Flow- ization in a particular field of medicine is [9] J. Buftle, R.S. Altmann, in 'Aquatic Sur- through (Bio)Chemical Sensors', Elsevier, required, i.e. additional years have to be face Chemistry. Chemical Processes at the Amsterdam, 1994. spent before claiming to be a specialist. Particle-Water Interface', Ed. W. Stumm, [23] N. Oreskes, K. Shrader-Frechette, K. Be- Wiley, New York, 1987,p. 351. Environmental systems are certainly at !itz, Science 1993, 263, 29I. [10] J. Buffle, R.S. Altmann, M. FileHa,Anal. [24] F. Reif, J. Chem. Educ. 1983,60,948. least as complicated as the human body. Chim. Acta 1990232, 225. [25] H. Rohde, 'G]obal Biogeochemica] Cy- There is, therefore, no hope to produce [I I] W.H. van Riemsdijk, L.K. Koopal, in 'En- c1es', Eds. S.S. Butcher, RJ. Charlson, environmental scientists with expertise vironmental Particles', Eds. J. Buffle and G.H. Orians, and G.V. Wolfe, Academic within 1-3years. The only thing wecando H.P. van Leeuwen, Vol. 1,lUPAC Envi- Press, London, 1992, Chapt. 4.