Pollutant partitioning for monitoring surface waters

This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies areencouraged to visit:

http://www.elsevier.com/copyright

http://www.elsevier.com/copyright

Author's personal copy

Pollutant partitioningfor monitoring surface watersD.A.L. Vignati, S. Valsecchi, S. Polesello, L. Patrolecco, J. Dominik

Monitoring of chemical pollutants following the European Water Framework Directive gives only marginal attention to their

partitioning among particulate, colloidal and truly dissolved phases, which is a crucial phenomenon in aquatic environments.

Proper consideration of issues related to pollutant partitioning would increase both the quality of monitoring data and their

usefulness for implementing adequate management strategies. This contribution highlights and discusses conceptual and tech-

nical challenges in properly considering pollutant partitioning in ecological and chemical assessment. We also consider the need

to improve integration of monitoring programs and fundamental research and suggest how to achieve such integration.

ª 2008 Elsevier Ltd. All rights reserved.

Keywords: Bioavailability; Colloid; Contaminant; Environmental quality standard; Filtration; Monitoring; Water Framework Directive

1. Introduction

The Water Framework Directive (WFD) ofthe European Union (EU) [1] considerswater and water management in a veryholistic way and sets the prevention of anyfurther deterioration of water bodies andthe protection and enhancement of thestatus of aquatic ecosystems as its primaryobjectives. Specifically, the WFD requiresthe achievement of ‘‘good status’’ (by 2015for all but heavily modified water bodies)based on the assessment of ecological andchemical quality compared with suitablereference conditions. Ecological status is anoverall expression of the quality of thestructure and functioning of aquatic eco-systems; while good chemical status is ob-tained when the concentrations of thepriority substances in water, sediment orbiota are below the Environmental QualityStandards (EQSs). The EQSs are set in aDaughter Directive (DD), which is at thefinal stage of the approval procedure at thetime of writing [2]. In order to transformthis bicephalous approach into an inte-grated one, there needs to be much betterconsideration of the processes controllingcontaminant mobility and bioavailabilityin aquatic systems.

The DD currently establishes EQSs for33 priority substances and specifies that:‘‘With the exception of cadmium, lead,mercury and nickel (hereinafter ‘‘metals’’)

the Environmental Quality Standards(EQSs) are expressed as total concentra-tions in the whole-water sample. In thecase of metals, the EQS refers to the dis-solved concentration (i.e. the dissolvedphase of a water sample obtained by fil-tration through a 0.45 lm filter or anyequivalent pre-treatment)’’.

This state-of-affairs for WFD-compliantchemical monitoring bears two majorcaveats:� On the one hand, establishing EQSs for

whole water or filtered water does notproperly address all the issues relatedto the distribution of pollutants be-tween the solid and the aqueousphases in the aquatic ecosystem [3,4].In particular, there is wide recognitionthat certain particularly hydrophobicsubstances may not be found in theliquid phase at significant concentra-tions. In such cases, it may be morepractical and pertinent to address thequestion of EQS compliance via moni-toring or assessment of concentrationsbound to suspended particulate matter(SPM). This environmental compart-ment is not explicitly considered inarticle 16.7 of the WFD (‘‘The Commis-sion shall submit proposals for qualitystandards applicable to the concentra-tions of the priority substances in sur-face waters, sediments or biota.’’) and

D.A.L. Vignati*

CNR-IRSA, V. le De Blasio 5,

70123 Bari, Italy

S. Valsecchi, S. Polesello

CNR-IRSA, Via della Mornera 25,

20047 Brugherio (Milano), Italy

L. Patrolecco

CNR-IRSA, Via Reno 1, 00198

Roma, Italy

J. Dominik

Institut F.-A. Forel,

Universite de Geneve,

Route de Suisse 10, 1290

Versoix, Switzerland

*Corresponding author.

Present address: CNR-IRSA, Via

della Mornera 25, 20047

Brugherio (Milano), Italy.

Tel.: +39 039 216 941;

Fax: +39 039 200 46 92;

E-mail: [email protected]

Trends in Analytical Chemistry, Vol. 28, No. 2, 2009 Trends

0165-9936/$ - see front matter ª 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2008.10.013 1590165-9936/$ - see front matter ª 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2008.10.013 159

https://www.researchgate.net/publication/240311010_DIRECTIVE_200060EC_of_the_European_Parliament_and_of_the_Council_of_23rd_October_2000_Establishing_a_Framework_for_Community_Action_in_the_Field_of_Water_Policy?el=1_x_8&enrichId=rgreq-8f0c24011c083424c0554fb6ca0d981e-XXX&enrichSource=Y292ZXJQYWdlOzIyMzA0ODA2NztBUzo5ODYwOTQxNjYzODQ4M0AxNDAwNTIxNzI3NzY1


its characterization also poses a number of analyticalchallenges (see Section 4).

� On the other hand, in the specific case of trace elements,simple reliance on filterable concentrations ignoresmost of the understanding achieved for these contami-nants over past decades [5,6] and disposes of the com-plex analytical issue of sample filtration (see Section4.4) by merely specifying a nominal filter cut-off.This article discusses how consideration of a few fun-

damental (Section 2), conceptual (Section 3) and ana-lytical issues (Section 4) related to pollutant partitioningamong the particulate, colloidal, and truly dissolvedphases can improve the environmental relevance ofmonitoring programs carried out in compliance with theWFD and related directives.

2. Fundamental issues

2.1. Introductory remarksContaminants entering aquatic systems are distributedamong particulate, colloidal, and truly dissolved phasesdepending on their intrinsic chemical properties (hydro-phobicity being especially important for organic micro-

pollutants), master parameters (e.g., pH, ionic strengthand redox potential), and other environmental factors(Fig. 1). This phenomenon, known as ‘‘partitioning’’,largely determines the environmental fate, bioavailability(defined here as the fraction of a contaminant which, in agiven compartment, is available for uptake by organisms)and biological effects of contaminants in aquatic systems(Fig. 1). A clear distinction must be made between traceelements, which are added in excess to natural back-ground concentrations, and man-made substances,which do not exist in nature. For a set of physico-chemicalconditions, the former may display a different geochemi-cal behavior depending on their origin (natural oranthropogenic), while the latter will partition accordingto their specific properties. The ubiquitous nature and thecrucial role of partitioning have several implications,which should be considered in order to improve the use-fulness of monitoring programs and provide field valida-tion of EQSs during implementation of the WFD.

2.2. Chemical aspectsThe DD specifications for priority substances address thepartitioning issues for both trace elements and organicmicrocontaminants in a simplified way.

Biological aspects-Environmental bioavailability

-Routes of exposure

-Trophic and indirect effects

- Feeding strategies

Physical aspects-Sedimentation

-Long distance transport

-Colloidal pumping

Technical / analyticalaspects-Sampling

-Sample preservation-Sample fractionation-Technical limitations-In situ techniques

Legal aspects-Sampling matrix

-Sampling frequency

-Sampling strategy (e.g., filtered vs. raw water)

Environmental factors-Master parameters

-Sediment-water interactions

-Hydrology

-Geology (metals only)

-Input variability

-Nature and concentration ofparticles and colloids

-Intrinsic pollutant properties

Modelling aspects-Contaminant partitioning(e.g., WHAM, EqP)

-Contaminant bioavailability(e.g., BLM, QSAR) Colloids

True solutionSPM

Figure 1. Centrality of contaminant partitioning for a number of ‘‘aspects’’ related to the implementation of the chemical-monitoring strategies ofthe Water Framework Directive (WFD) of the European Union. Full arrows indicate well-established or well-considered relationships infundamental research and/or in technical-regulatory issues. Dotted arrows indicate relationships that are less studied in fundamental researchor have received little consideration during the definition of the chemical-monitoring strategies proposed by the WFD. Refer to text for moredetails on the various ‘‘aspects’’ reported in this figure.

Trends Trends in Analytical Chemistry, Vol. 28, No. 2, 2009

160 http://www.elsevier.com/locate/trac


For organic priority substances (PSs), whole water isindicated as the matrix for EQS compliance, with no con-sideration of how differences in the hydrophobicity of PSswould influence their partitioning between filterable andparticulate phases. Organic PSs with low Kow(<104)would show a larger affinity for the filterable phase, whilemore hydrophobic substances (Kow > 104) would prefer-entially adsorb onto SPM. Fundamental knowledge wouldtherefore suggest that analyses of the filterable phase arebetter suited for monitoring of contaminants withKow < 104; while determinations of the SPM-bound frac-tion are absolutely needed for more hydrophobic con-taminants.

To avoid filtration artifacts (Section 4.4), it was alsoproposed to analyze only SPM in all cases and thenestimate filterable concentrations through the partitioncoefficients (e.g., Kow, Koc) [7]. However, the use ofpartitioning theory for predicting filterable pollutantconcentrations from those measured in SPM and viceversa has not been considered reliable by the Analysisand Monitoring of Priority Substances (AMPS) expertgroup [8]. Experimental evidence (e.g., [9,10]) indeedconfirmed that simple equilibrium models of partitioningunderestimate the contribution of the SPM-bound frac-tion to the concentration in whole water. Furthermore,partitioning between SPM and the filterable phase maynot be at equilibrium in field situations and show con-siderable spatial and temporal variability due to changesin river discharges and SPM quality and amount. Forthese reasons, the AMPS expert group highlighted theneed to monitor both filterable and SPM-bound con-centrations of organic PSs.

In the case of trace metals, EQSs are fixed for watersamples filtered at 0.45 lm (or any equivalent method).This choice was probably meant to measure what isnormally considered the most bioavailable metal fraction[5] and, at the same time, to avoid large variations dueto different geochemical background levels of trace ele-ments in SPM from different (sub)basins. However, metaldistribution between filterable and particulate phases is

determined by several factors (Fig. 1) and the contribu-tion of filterable and particulate pathways to metal bio-accumulation and toxicity can be highly variable(Section 2.3). Furthermore, the importance of the filter-able pathway, specifically for mercury accumulation inhigher organisms, can be very limited. As in the case oforganic PSs, the need to monitor both filterable andSPM-bound concentrations has become evident and hasalready been recommended [11].

Furthermore, Town and Filella [12] showed that0.45-lm filtration does not provide enough informa-tion for properly understanding the fate of elementsand that the colloidal phase (Section 4.5) also needs tobe considered. The fraction of metals associated withcolloids may be quite considerable (Table 1), but itvaries over a wide range for reasons that are not yetcompletely understood [13,14]. In surface waters,similar results have been reported for polyaromatichydrocarbons (PAHs) [15] and endocrine disruptors[16], whose colloidal fraction varies from 0 to nearly100%, depending on the specific substance and thecharacteristics of the aquatic system.

More consideration of partitioning issues in WFD-compliant monitoring is clearly necessary to obtainadequate information about the environmental fate ofthe various pollutants and, in turn, their bioavailabilityand toxicity (Fig. 1). Management strategies, decisions,and interventions based on ‘‘good quality’’ ecologicalobjectives also greatly depend on knowledge of the fate ofpollutants. Even if theoretical frameworks (e.g., Equilib-rium Partitioning Theory – EqP) and geochemicalmodels (e.g., WHAM and SCAMP [17]) provide usefulhints about the likely environmental fate of pollutants,much remains to be done to ensure that theoretical andmodel predictions apply to real situations [17,18]. Vali-dation of any partitioning model would obviously re-quire a large database of detailed measurements for arange of contrasting aquatic systems. Data are particu-larly needed with regard to distribution of contaminantsbetween colloids and true solution.

Table 1. Mean ± 1 standard deviation (s.d.) of the upper and lower limits of ranges for the fraction of metals associated with colloids (expressedas percentage of ‘‘total filterable’’ metal concentrations) (based on references collected in [13,14] and on original studies [83,84])

Ni Pb Cd Hg MeHga

lower upper lower upper lower upper lower upper lower upper

FreshwaterMean 15 33 61 93 21 40 15 84 17 78s.d. 13 17 27 6 15 20 n.a. n.a. n.a. n.a.N 10 10 8 7 4 4 1 1 1 1Estuaries and coastal seaMean 12 36 22 72 4 42 28 74 23 45s.d. 18 20 22 24 7 17 9 12 n.a. n.a.N 7 7 4 4 9 9 3 3 1 1

N, Number of data available for calculations of the means; n.a., Not applicable.aMeHg, Methyl mercury.


http://www.elsevier.com/locate/trac 161


We believe that characterization of colloids and theirseparation from true solution remain technically toodemanding (Section 4.5) to become a regular feature ofWFD-compliant monitoring programs. However, thestudy of contaminant partitioning between colloids andtrue solution at selected locations and during the earlyphases of WFD implementation would present a uniqueopportunity to satisfy the basic data needs for thisimportant issue. Such a hypothetical database, coveringthe largest possible range of typical situations forparameters (e.g., hydrological regime, SPM, pH, ionicstrength, hardness, and dissolved organic carbon) wouldbe invaluable to refine the available modeling tools forcontaminant partitioning and expand their use inmonitoring programs and management strategies(Fig. 1). For cases outside the ‘‘typical situations’’,additional specific investigations may be performed tocheck the applicability of models.

‘‘Specific investigations’’ will be most often neededfor unstable systems (e.g., rivers, streams, and coastalmixing zones, where hydrological and chemicalparameters can change rapidly and markedly). In sta-ble systems, a pseudo-steady state can be attained ra-ther easily and surface reactive contaminants followthe sequence adsorption-aggregation-removal; a pro-cess called Brownian pumping or colloidal pumping[19,20]. Such a sequence also exists in unstable sys-tems, but it is frequently perturbed by sudden changesin the input of contaminants (watershed erosion andresuspension of river-bed sediment), hydrodynamicconditions and chemical parameters, especially duringstorm events or following the inflow from tributaries orpoint discharges. In unstable systems, it therefore be-comes much more difficult to predict the environmen-tal fate and effects of contaminants. Properlycombining monitoring and modeling seems the bestway to deal with such systems and is also the mostviable way for Member States to designate mixingzones in river-basin-management plans according toArticle 4 of the Directive on EQSs [2].

2.3. Biological aspectsAccording to the WFD, control of chemical substancesis targeted at preventing toxic effects on ecosystems.This aim should be achieved by compliance checkingto EQSs for priority substances in water, sediment orbiota. Recent research shows that proposed EQSs forCd, Ni, and Pb appear sufficiently protective for aquaticbiota [21]. However, the water-based EQSs establishedby the DD do not differentiate between particle-bound,colloidal, and truly dissolved pollutant fractions, andpartitioning usually receives little consideration in theprocess for drawing up EQSs [3,4]. However, pollutantpartitioning has a number of important implications indetermining the biological effects of a given contami-nant (Fig. 1):

� Environmental bioavailability. There is now ample evi-dence that the priority trace elements included in theDD and many organic pollutants strongly bind to sus-pended matter and colloids. Adsorption onto orabsorption into SPM and colloids can make a consider-able fraction of a pollutant unavailable for someorganisms (e.g., toxicity of metals to algae is usuallyreduced in the presence of colloids), but more availablefor others (see paragraph below on Dietary exposure).Most knowledge on the influence of colloids on metalbioavailability is derived from studies on model colloids[22–24] and needs to be verified in natural conditions[25]. Similarly, for hydrophobic organic pollutants, ithas often been assumed that only compounds presentin solution (i.e. truly dissolved phase) will be availablefor uptake via diffusion across the cell wall and, in plu-ricellular organisms, across epithelial boundaries (e.g.,gills or body/gut walls). While it is reasonable to sur-mise that organic pollutant bioavailability will gener-ally decrease with increasing sorption onto solids,more research on the effect of colloids (model and nat-ural) in controlling the environmental bioavailabilityof organic pollutants is needed.

� Dietary exposure. Animal guts represent chemicalreactors in which animals solubilize nutrients fromthe ingested material into an absorbable form[26]. Particles and colloids entering ‘‘gut environ-ments’’ encounter conditions quite different fromthose in the external environment. Pollutants boundto particles and colloids can then undergo desorp-tion during transport and digestion in the gastroin-testinal tract; which enhances the bioavailability oforganic pollutants and metals in the digestive fluid.This additional pollutant uptake route has been ob-served for bivalves, oligochaetes, fish, and crusta-ceans [27–30].

� Direct uptake of particle and colloids. Besides ingestion,particle and colloids can directly cross epithelialboundaries (e.g., gills or body wall). Prokaryotes arelargely protected against this exposure pathway be-cause they lack mechanisms for transport of colloidalparticles across the cell wall; while eukaryotes caninternalize nanoparticles (NPs) or microparticles viaendocystosis and phagocytosis [31]. In ternarysystem organism–pollutant–particle, several scenar-ios are possible. If particles do not enter the cells,they can adsorb or absorb the pollutants (therebymodifying environmental bioavailability) or, as inthe case of some metallic NPs, they can partiallydissolve and cause toxicity by increasing the (truly)dissolved concentration of specific trace elements[32]. If the particles with the associated pollutantsare taken up by the cells, then biological effects couldbe caused by the pollutants, the particles themselves,or both. However, it can also happen that no effect isobserved if the particle-bound pollutants are stored in




an inert form inside the cell and the particle itself isnot toxic. Possible effects and risks from directparticle uptake are particularly relevant to theincreasing introduction of engineered NPs in aquaticsystems and will require case-by-case evaluations infuture [31,33].

� Quality/content of organic matter of the particles. Organ-ic matter content and type affect the rate of ingestionof SPM and colloids by organisms [34,35]. Ingestionrates determine gut-throughput time and thereforecan influence the extent of digestive reactions andthe absorptive gains of energy, nutrients and pollu-tants. The importance of gut-throughput time fordetermining contaminant uptake will in turn dependon the kinetics of pollutant desorption from the in-gested particles. Uptake should be increased in situa-tions when animals characterized by long gut-throughput times ingest material containingweakly-bound or rapidly-desorbing contaminants.Consequently, complex and counter-intuitive resultscan be obtained depending on which exposure routeprevails (i.e. uptake from dissolved fraction or uptakefrom ingested matter), the rate of ingestion, and thedesorption processes [36]. These observations arevery relevant to the WFD because particulate vs. fil-terable (and much less so colloidal vs. truly dissolved)organic carbon pools are not explicitly includedamong the physico-chemical parameters to be moni-tored under Annex V (‘‘to ensure the functioning ofthe type specific ecosystem and the achievement ofthe values specified above for the biological qualityelements’’).

� Trophic and indirect effects. SPM and colloidal materialinclude biological components (algae, bacteria andprotozoa), which can be a simultaneous source ofenergy and toxicants (see paragraph above on Dietaryexposure) to higher organisms. Moderate nutrientenrichment can stimulate primary productivity and,consequently, overall ecosystem productivity and thegeneral health of aquatic organisms. Good physiolog-ical conditions may exert compensatory or maskingaction on the biological effects of inorganic and organ-ic contaminants [37]. Furthermore, somatic growthdilution of trace contaminants is observed in growingorganisms, whereby biomass-corrected concentrationof pollutant diminishes as cells divide. Finally, a givenamount of aqueous pollutants partitioning to ‘‘biolog-ical SPM or colloids’’ will present a much lower risk inbloom situations, when a rapid growth of primaryproducers (e.g., phytoplankton) would yield a lowerconcentration of pollutant per cell (bloom dilution).How these processes influence the effects of pollutionalong freshwater food webs has not yet been studieddeeply [38,39].Even with such a schematic overview, it is clear that

consideration of all the biologically relevant aspects of

partitioning goes beyond technical, human and eco-nomical possibilities of the best-funded monitoring pro-gram. However, the fundamental research behind theprocess of defining EQSs ought to consider these issues asneeded. For this, two lines of research deserve particularattention:� The quest to determine the bioavailable fraction of aquatic

contaminants. Bioavailability of aquatic contaminants(in the broad sense of contaminant uptake by all pos-sible exposure routes) has been a major researchtarget for several decades, as soon as it became clearthat total concentrations of contaminants wereunsuitable to predict their uptake and toxicity. TheBiotic Ligand Model (BLM) has been successfully usedto predict Cu toxicity in natural waters, but much re-mains to be done to predict adequately bioavailabilityor toxicity of contaminants in natural systems fromchemical data or from laboratory bioassays [40]. Sim-ilarly, quantitative structure-activity relationship(QSAR) models have greatly helped in modeling eco-toxicological parameters for organic compounds, butthe extent to what they should be used is still a matterof debate [41,42], and validation of QSAR predictionin natural systems would clearly be beneficial in con-troversial situations.

� The generally over-protective character of EQS, linked tothe way in which they are derived [3]. This is of moreconcern for ecotoxicologists, but has importantrepercussions also on the activity of environmentalchemists. Over-protective EQSs could lead to discrep-ancies between ecological and chemical status dur-ing monitoring programs (e.g., good ecologicalstatus accompanied by non-compliance with oneor more EQSs). In such cases, given the difficultiesof reproducing the relevant natural scenarios incontrolled laboratory conditions, in situ biologicalinvestigations (along with specific chemical mea-surements – see Section 4.6) appear to be the mosteffective strategy to verify if chemical pollution canhave potential toxic effects and requires remedial ac-tion. A large number of in situ biological tools existand schemas for their use in monitoring programshave already been proposed [43]. Because of theever increasing number of chemicals introduced inthe environment, ‘‘in situ validation’’ of EQSs [3]will become increasingly desirable as a decision toolwhen ecological and chemical monitoring yield con-trasting results. ‘‘In situ validation’’ could effectivelyensure that EQSs are neither under-protective,which could lead to environmental damage, norover-protective, which would result in unnecessaryexpenditure. In order to better understand the limi-tations of applying laboratory-derived EQSs to com-plex environmental realities, more innovative andflexible conceptual approaches to chemical monitor-ing must be developed.




3. Conceptual issues

By proposing an ecological approach to the classificationof aquatic systems, the WFD dramatically increased theenvironmental relevance of the EU regulatory frame-work. Such a revolution spawned a huge, coordinatedeffort by the European ‘‘ecological scientific community’’to produce the necessary knowledge (e.g., definition ofwater-body types and reference conditions) and tools(e.g., suitable biological indexes or indicators) to satisfythe requirements of the new legislation (e.g., [44,45]).Unluckily, much less attention has been devoted to theresearch needs related to the ‘‘chemical status’’ aspectsof the WFD, especially to ensure that the ‘‘chemicalmonitoring’’ procedure is sufficiently informative of therisks associated with the various chemicals. Theseaspects are very critical in situations of regulatory non-compliance due to chemical contamination by (priority)pollutants. In particular, the current level of funda-mental knowledge really offers sufficient grounds toadvocate better consideration of pollutant partitioning inmonitoring programs, in the definition of monitoringstrategies, and, more in general, in the process ofderiving EQSs for priority substances.

Practically speaking, the chemical-monitoring strat-egy currently proposed in the WFD and DD and based onbroadly applicable EQSs (Type 1 EQS, according to [3]) isprobably adequate to identify cases of unsatisfactoryecological status that can be tracked down to prioritysubstances or other regularly monitored pollutants.However, the same strategy, given its little considerationfor fundamental issues, would be unsuitable for devel-oping adequate remediation strategies.

Better consideration of pollutant partitioning wouldretain its importance even in ‘‘alternative EQS scenarios’’where environmental standards are established for bedsediments or biota [i.e. the critical body residue (CBR)approach] [46]. For developing sediment-based EQSs,knowledge of pollutant concentrations bound to SPMand of the quantitative importance of the mechanismssequestering pollutants to the sediments (i.e. sedimen-tation and colloidal-pumping [19,20]) is an obviousrequirement. In a CBR approach to developing EQSs,realistic exposure scenarios (proper consideration ofpollutant partitioning being one factor among others)must be employed to derive environmentally meaningfulstandards and to minimize uncertainties in laboratory-to-field extrapolation [47].

Conceptually speaking, the major drawback of thechemical-monitoring strategy currently endorsed bythe EU is that it retains a policy-driven (or possibly adiscipline-driven) rather than an issue-driven approach[48]. This is understandable and, given the conserva-tive nature of EQSs (see Section 2.3), would provide asufficient degree of protection in most cases. However,the use of over-conservative standards might result in

a dispersion of technical, human, and economic re-sources, a possibility that justifies more fundamentalapproaches to drawing up EQSs and chemical moni-toring in general.

In an interdisciplinary context, it is also possible toconsider at which point (and to what degree of technicalsophistication) it would be necessary to deploy ‘‘chemi-cal tools’’ during a monitoring program. A ‘‘not good’’ecological status may well be caused by other factors(e.g., physical disturbance and habitat loss). To eliminatethis possibility, standardized ecotoxicological tests wouldprobably be a better tool than chemical measurements. Ifthe ‘‘laboratory ecotoxicology’’ points to a ‘‘chemical-culprit’’, then a detailed ‘‘Effect-Directed Analysis’’ (EDA)procedure can be implemented. With this strategy, rou-tine chemical monitoring (based on a fixed number ofparameters and analytical techniques) could be com-pleted, when necessary, by ad hoc analyses based on themost recent scientific findings and employing the latestanalytical tools.

This interdisciplinary way of working is particularlyattractive considering that physical, chemical and bio-logical variability of the European natural surface waters(and the complexity of the anthropogenic impacts) isindeed too big to be addressed with ‘‘one-fits-all’’schemes for chemical-monitoring programs. Minimalstandardization of sample collection, handling and pre-treatment, chemicals to monitor and analytical proce-dures to follow is obviously necessary. However, therealso needs to be guidance on additional procedures forcases in which conventional monitoring fails to providethe required information.

4. Analytical issues

4.1. Introductory remarksNatural waters are heterogeneous matrices in whichparticles of various sizes and chemical nature are sus-pended in an aqueous phase. At present, a three-phasemodel comprising a particulate (SPM), colloidal and trulydissolved phase is considered sufficiently accurate torepresent such complex environmental reality [49,50].Note however that SPM and colloids constitute a dimen-sional continuum [50] and any clear-cut distinctionamong the three phases is operational in nature. Well-established (e.g., laser diffraction) [51] and innovativetechniques {e.g., single-particle counting (SPC) [52],field-flow fractionation (FFF) [53], and laser-inducedbreakdown spectroscopy (LIBS) [54]} are progressivelyallowing scientists somehow to ‘‘see’’ this continuum andthe distribution of some contaminants across it. Theapplication of most of these techniques in routine moni-toring is nowhere in sight and is probably unnecessary.Nonetheless, information gained from such techniquescan greatly help in interpreting monitoring data, provided




that SPM vs. filterable partitioning is duly considered andthat data quality and comparability are guaranteed.

4.2. Sampling of SPMSampling of SPM holds interest in reliably measuring thetotal concentrations of organic pollutants [11] and inaccounting for dietary exposure for trace elements (Sec-tion 2.3). Filtration artifacts (Section 4.4) are unlikely toaffect the measured concentrations of SPM-bound con-taminants and filtration could, in principle, provide bothaqueous and solid matrices for contaminant analysis.However, problems are likely to be encountered in watershaving high SPM concentrations (meaning rapid filterclogging and highly skewed results for filterable concen-trations) or when comparatively large amounts of SPMare needed for subsequent analysis, as may be the case fororganic contaminants requiring different extraction pro-tocols. An alternative to filtration is continuous-flowcentrifugation (CFC), which is a well-established tech-nique used to collect large amounts of suspended solids innatural surface waters. Chemical characterization of SPMcollected by filtration (0.45 lm) and CFC usually comparefavorably for water containing large amounts of (inor-ganic) suspended solids [55–57]. However, the situationdiffers for waters having low ionic strength, low levels ofSPM, or relatively high amounts of organic matter; wherecomparison of results from filtration and CFC is lessstraightforward [58,59]. Finally, the possibility of usingCFC effluent for analysis of the filterable fraction variesand should be subjected to case-by-case evaluation[57,60]. If needed, specific guidance on when and how tocombine results from filtration and CFC will have to beprovided and data-harmonization issues analogous tothose described by Forstner [61] for bed sediments con-sidered.

4.3. Specific SPM issues for organic contaminantsCompliance with EQS values for organic compoundsrefers to whole-water samples. Whole-water data may begenerated by analysis of the whole-water sample or byseparate determinations on filterable and solid phases.The use of widely applied extraction techniques [e.g.,liquid-liquid extraction (LLE) and solid-phase extraction(SPE)] on unfiltered samples does not assure the quan-titative extraction of hydrophobic organic substancesadsorbed on SPM ([11] and our unpublished results). Asa consequence, ‘‘whole-water measurements’’ in SPM-rich waters may lead to underestimation of pollutantconcentrations, especially for highly hydrophobic sub-stances. Such underestimation may in turn produce anincorrect allocation of the status of water bodies andmisinterpretation by decision-makers.

On a European scale, another potential problem forthe analysis of organic contaminants could be poor datacomparability between different laboratories and coun-tries, even if internationally recognized standard

methods are used. In the large majority of the standardmethods designed for the determination of organic con-taminants in water [11], the problem of properly ana-lyzing whole-water samples has not been consideredexplicitly. Most standard methods have been validatedonly for filtered water samples and provide no or littletechnical information (e.g., generic sentences such as‘‘. . .filtration of the sample where appropriate. . .’’) onhow to deal with SPM when analyzing whole-watersamples [11,62]. The available standard methods needto be amended to define specifically their domains ofapplication to specific matrices (e.g., transitional andcoastal waters, waters with high SPM levels). One mainissue is to find agreement between the concept of ‘‘watercompartment’’ addressed by the WFD and the scope ofCEN (Comite Europeen de Normalisation) standards,which typically include all water types (up to 20 g/L ofSPM), but are not completely validated for complexmatrices.

Recently, in the call for tenders related to MandateM424 (Mandate for standardization addressed to CEN forthe development or improvement of standards in supportof the Water Framework Directive) received by theEuropean Commission, CEN expressly suggested testingmembrane-extraction disks as a potential tool for whole-water analysis. Nevertheless, this analytical approachstill needs to be assessed by targeted research studies.

4.4. Filtration for trace-element analysisThe suggestion of filtration as the preferred method forsample fractionation prior to trace-element analysisstems from its relatively simple logistical requirementsand from the possibility of on-line filtration in situ. Thesetwo factors make filtration the most attractive techniquewhen small amounts of sample suffice and/or the num-ber of samples is limited [63]. The choice of the 0.45-lmthreshold for filtration seems to be mainly for historicalreasons (after Goldberg et al. [64]). This strategy bothneglects the existence of colloids and its consequences(see Section 2) and trivializes the complex issue of samplefiltration (Table 2). Many factors other than filter pore-size are known to affect the ‘‘filterable concentration’’measured in an aqueous sample markedly ([65,66] andreferences therein). A detailed guideline on sampling andsample processing will have to be provided to ensure thatchemical status for trace elements is uniformly assessedacross the EU Member States. There is also a need forspecific guidance on what constitutes ‘‘. . .any equivalentpre-treatment’’ that could be used instead of filtration.

Finally, in the case of Hg, the use of an EQS for thewater compartment poses specific sampling require-ments and analytical challenges [11,67], leading toadditional sampling efforts and to the inability of manylaboratories to provide data on Hg concentrations inwaters. A Hg-EQS for water is also questionable from afundamental point of view, given that the risks associ-




ated with Hg arise from the strong biomagnification ofmethyl-Hg along the food chain. The DD [2] partly rec-ognizes the peculiar characteristics of Hg and allowsEQSs for biota to be used. With this option (CBR ap-proach, [46]), Hg concentrations would be measureddirectly in exposed organisms that integrate Hg exposureover time and over the different exposure routes (i.e.particulate, colloidal, and truly dissolved). EQSs for biotacould therefore automatically take into account Hgpartitioning (and speciation), but only if some concep-tual aspects discussed in Section 3 and also highlightedin [47] are properly considered in the process of drawingup the EQS.

4.5. Sampling of colloidsColloids are defined as particles having at least onedimension in the range 1 nm�1 lm [68] and theirsampling is not considered in the regulatory frameworkof the WFD. This situation is unlikely to change in theforeseeable future, given the difficulties of preserving theintegrity of the colloidal size-distribution (and the asso-ciated contaminant partitioning) during sampling andsample handling and because of the resource-intensive

and labor-intensive techniques needed to sample col-loids. However, a brief reminder of the state-of-the-art ofcolloidal sampling is beneficial in considering the needfor better integration of the scientific findings of thefundamental research on colloids in the regulatorycontext (see Section 3).

Aquatic colloids can be studied in unperturbedsamples [69] or in size-fractionated samples [70,71]using various techniques (Table 3). Size fractionationand analysis of environmental colloids is an area wheresignificant advances have been made in recent years.Cross-flow ultrafiltration (CFUF) can now be regarded asthe standard method for separating colloids and truesolution. However, the fractionation is often inconsistentwith the nominal pore sizes of CFUC membranes andmay not be fully quantitative. Because of these draw-backs, there is still great variability in results in the lit-erature with respect to the proportion of chemicalsbound to the colloidal fraction (Table 1 and Section 2.2).Some of this variability also stems from the lack ofstandardized methods for CFUF, which faces issues sim-ilar to conventional filtration (Table 2) and specificproblems [72].

Many of our difficulties in better understanding theenvironmental role of colloids result from technicalinability to characterize them without introducing arti-facts during the measurement process. Several processes(e.g., aggregation, oxidation, microbial degradation, and

Table 3. Overview of the available techniques for separation andanalysis of colloids in surface waters (after [52,85–88] andreferences therein)

Type of technique Method

Microscopic Transmission electron microscopy(TEM)Environmental scanning electronmicroscopy (ESEM)Atomic force microscopy (AFM)

Spectroscopic Laser-induced breakdown spectroscopy(LIBS)X-ray absorption spectroscopy (XAS)Fluorescence correlation spectroscopy(FCS)Single-particle counter (SPC)

Fractionation Centrifugation (CF)Ultrafiltration (UF)Cross-flow ultrafiltration (CFUF)Field-flow fractionation (FFF) (Sd, FI, Th,El, Gr)Split-flow thin cell (SPLITT)

In situ passive samplers Diffusive gradients in thin film (DGT)Diffusive equilibration in thin films(DET)Stripping voltammetry (SV)Permeation liquid membrane (PLM)

Sd, Sedimentation; FI, Flow; Th, Thermal; El, Electrical; Gr,Gravitational.

Table 2. Potential artifact sources and resulting artifacts arisingfrom oversimplification of the ‘‘sample-filtration issues’’ inlarge-scale monitoring programs within the WFD and DD frame-work (after [65,66])

Potential artifact source Potential resulting artifact

Sample-handling issues -Incomplete recovery ofsuspended particulatematter (SPM)-Colloidal coagulation-Loss of sample homogeneity-Loss of analytes-Inadequate storage resultingin modification of contaminantpartitioning

Variability in filter type andmanufacturer

-Adsorption-Contamination-Filter clogging-Lack of data homogeneity

Filtration methodology -Colloidal coagulation-Cake formation-Filter clogging-Incomplete recovery ofsuspended particulatematter (SPM)

Suspended particulate matter(SPM) variability in naturalsamples (Filter load)

-Variability of filtrationefficiency-Clogging

Distribution and type ofcolloidal material

-Variability of filter behavior




dissolution) can markedly alter the size distribution andother properties of colloids with obvious consequencesfor the following analyses. Changes in colloid propertiesbegin immediately after sampling and become significantwithin a few hours [50,73,74]. Sample preservation isthe major obstacle preventing routine measurement ofcolloidal distribution and associated contaminants inmonitoring programs, given that the above-mentionedchanges can be even quicker if the sample undergoessome form of treatment [74].

These problems with sample preservation prevent theroutine use of many cutting-edge instruments (e.g., FFF,LIBS, and capillary electrophoresis, Table 3) that are toodelicate or have too many requirements to be trans-ported and used on site. Recent studies with on-sitemeasurements of colloidal distribution [75] or the use ofin situ techniques to distinguish between free and col-loidally-bound metals ([76] and Section 4.6) hold par-ticular potential for reconciling the practicalrequirements of monitoring with adequate considerationof fundamental issues.

As already stated, we think that sampling and char-acterization of colloids are unlikely to find a permanentplace in monitoring programs. However, in the case ofsome trace metals, there is already evidence that infor-mation on colloids vs. true-solution partitioning can beobtained from simple routine measurement of filterableconcentrations that are easily implemented in monitor-ing programs [77]. Development and validation ofanalogous models for other metals and contaminantswill require a significant contribution by environmentalchemists.

4.6. Passive samplers and in situ toolsWFD-compliant technical monitoring is implicitly basedon the logistically advantageous strategy of collectingsamples for subsequent laboratory analysis. Besides thepossible fundamental drawbacks of discrete samplingstrategies (due to the impossibility of accounting for allthe variables that influence pollutant mobility and bio-availability in the field), sample modifications can occurvery shortly after, or even upon, sample collection[73,74]. In situ passive samplers {e.g., diffusive gradientsin thin-film (DGTs) [76], semi-permeable membrane de-vices (SPMDs) [78], and ad hoc field probes for elementspeciation [79]} would represent an attractive solutionto alleviate these problems. Passive samplers providetime-averaged monitoring of contaminant concentra-tions and markedly increase the analyte concentrationfor those pollutants whose measurement at or below EQSlevels is problematic [11].

However, the behavior of passive samplers with regardto pollutant partitioning (including the possibility ofcontaminant re-supply from the particulate phase) is notcompletely understood and can vary depending on thetechnical solution adopted for a specific sampler, the

intrinsic characteristics of the contaminant, and theenvironmental conditions ([76,78,79] and referencestherein). At present, the use of passive samplers to checkfor compliance with EQSs is therefore neither defendablenor feasible. However, these devices deserve properconsideration when conventional monitoring studieshighlight the need for additional detailed studies (Section2).

In particular, passive samplers and in situ probeshold great potential for cross-validating chemicalmeasurements and biological results under field con-ditions. Contrary to conventional monitoring methods,passive samplers usually measure only a fraction ofthe total-pollutant concentration in a given environ-mental compartment. However, to the best of ourknowledge, it is still unclear if fractions such as DGT-labile metals, soluble voltammetrically-labile complexes[77] or SPMD-sequestered contaminants can predictbiological effects under field conditions. An affirmativeanswer to this question would spawn a real revolutionin environmental monitoring, but faces two majorchallenges:� From a technical point of view, suitable in situ tech-

niques for all the pollutants of interest must be devel-oped and refined. For example, conventional DGTmembranes are not capable of sequestering Hg. Spe-cific DGT devices for Hg already show great potential,but their application has been rather limited so far[80,81].

� From a conceptual point of view, a broad interdisciplin-ary approach to environmental problems [82] andconstant cross-validation between chemical and bio-logical measurements are needed to obtain a thor-ough evaluation of the capabilities of passivesamplers. In situ biological tools (e.g., caging devicesfor the exposure of laboratory-reared organisms di-rectly in the field) are already available [43] and envi-ronmental chemists should become more aware of theinformation that they can provide for the analyticaldevelopment of in situ techniques.

5. Conclusions

Choosing to neglect partitioning issues in WFD-com-pliant chemical-monitoring programs has no scientificjustification, and, as can be inferred from the discus-sion above, it has several potential pitfalls in terms ofboth environmental security and water management.

Short-term solutions should focus on defining detailed,standardized strategies for sample fractionation in orderto ensure that at least SPM-bound and filterable pollu-tants are measured separately.

Medium-term solutions require refinement and devel-opment of in situ devices capable of measuring (at leastapproximately) the bioavailable contaminant fraction in




environmental matrices (in addition to the previousrecommendations of Coquery et al. [11] on analyticaldevelopments).

Note that in-depth cooperation between chemistryand ecotoxicology (and all related disciplines) will beinstrumental in determining the degree of ‘‘environ-mental success’’ of any analytical effort. Furthermore,the WFD can be significantly improved by proposing,developing, and validating harmonized in situ strate-gies to be implemented in those cases when the causesof non-compliance are unknown or uncertain.

Long-term solutions go beyond technical problemsand require increased interdisciplinary thought in thedefinition of monitoring strategies and managementplans, close (ideally early-stage) coordination amongmonitoring and management programs and funda-mental investigations, and explicit requirements of fieldvalidation for key, laboratory-derived results.

Complex pieces of legislation, such as the WFD, areusually the outcome of long negotiations, and theenhancement brought about by the WFD in the overallsurveillance of European water bodies is unquestionable.Nonetheless, environmental science and societal re-sponses to environmental issues continually evolve andit is also scientists� duty to ensure that environmentallegislation is updated according to the latest analyticaland conceptual developments.

AcknowledgementJ. Dominik and D.A.L. Vignati acknowledge the supportof the Swiss National Science Foundation forfunding various projects (grants 20-57189.99,20-65098.01, 200020-101844, 200020-109608, and200020117942/1) which were instrumental for devel-oping many of the ideas presented in this paper.

References[1] European Commission, Directive 2000/60/EC of the European

Parliament and of the Council of 23 October 2000 establishing a

framework for Community action in the field of water policy, Offic.

J. Eur. Commun. L 327 (2000) 1.

[2] European Commission, Proposal for a Directive on environmental

quality standards in the field of water policy and amending

Directive 2000/60/EC, COM(2006)397, European Commission,

Brussels, Belgium, 2006.

[3] M. Reiley, W.A. Stubblefield, W.J. Adams, D.M. Di Toro,

P.V. Hodson, R.J. Erikson, F.J. Keating Jr. (Eds.), Reevaluation of

the State of the Science for Water-quality Criteria Development,

SETAC, Pensacola, FL, USA, 2003.

[4] P. Lepper, Identification of quality standards for priority sub-

stances in the field of water policy. Towards the derivation of

quality standards for priority substances in the context of the

water framework directive. Final Report of the Study Contract No.

B4-3040/2000/30637/MAR/E1, Fraunhofer Institute, Germany,

2002, p. 124.

[5] A. Tessier, D.R. Turner (Editors), Metal Speciation and Bioavail-

ability in Aquatic Systems, John Wiley and Sons, Chichester, UK,

1995.

[6] J.S. Meyer, W.J. Adams, K.V. Brix, S.N. Luoma, D.R. Mount,

W.A. Stubblefield, C.M. Wood (Eds.), Toxicity of Dietborne Metals

to Aquatic Organisms, SETAC, Pensacola, FL, USA, 2005.

[7] F. Smedes, Int. J. Environ. Anal. Chem. 57 (1994) 215.

[8] AMPS Expert Group, Contributions of the Expert Group on

Analysis and Monitoring of Priority Substances to the Water

Framework Directive Expert Advisory Forum on Priority Sub-

stances and Pollution Control, Report EUR 21587 EN, Ispra (VA),

Italy, 2005, pp. 133.

[9] L. Patrolecco, S. Capri, S. De Angelis, R. Pagnotta, S. Polesello

S. Valsecchi, Water Air Soil Pollut. 172 (2006) 151.

[10] O.P. Heemken, B. Stachel, N. Theobald, B.W. Wenclawiak, Arch.

Environ. Contam. Toxicol. 38 (2000) 11.

[11] M. Coquery, A. Morin, A. Becue, B. Lepot, Trends Anal. Chem. 24

(2005) 117.

[12] R.M. Town, M. Filella, Rev. Environ. Sci. Biotechnol. 1 (2002)

277.

[13] F.J. Doucet, J.R. Lead, P.H. Santschi, in: K.J. Wilkinson, J.R. Lead

(Editors), Environmental Colloids and Particles, Wiley & Sons Ltd.,

Chichester, UK, 2007, pp. 95–157.

[14] L. Guo, P.H. Santschi, in: K.J. Wilkinson, J.R. Lead (Editors),

Environmental Colloids and Particles, Wiley & Sons Ltd., Chich-

ester, UK, 2007, pp. 159–221.

[15] O. Gustafsonn, N. Nilsson, T.D. Bucheli, Environ. Sci. Technol. 35

(2001) 35.

[16] J.L. Zhou, R. Liu, A. Wilding, A. Hibberd, Environ. Sci. Technol.

41 (2007) 206.

[17] S. Lofts, S.E. Tipping, Sci. Total Environ. 251/252 (2000) 381.

[18] J.B. Butcher, E.A. Garvey, V.J. Bierman Jr., Chemosphere 36

(1998) 3149.

[19] B.D. Honeyman, P.H. Santschi, J. Mar. Res. 47 (1989) 951.

[20] B.D. Honeyman, P.H. Santschi, in: J. Buffle, H.P. van Leeuwen

(Editors), Environmental Particles, Vol. 1, Lewis Publishers, Boca

Raton, FL, USA, 1992, pp. 379–423.

[21] M. Crane, K.W.H. Kwok, C. Wells, P. Whitehouse, G.C.S. Lui,

Environ. Sci. Technol. 41 (2007) 5014.

[22] P.G.C. Campbell, M.R. Twiss, K.J. Wilkinson, Can. J. Fish. Aquat.

Sci. 54 (1997) 2543.

[23] B. Koukal, C. Gueguen, M. Pardos, J. Dominik, Chemosphere 53

(2003) 953.

[24] B. Koukal, P. Rosse, A. Reinhardt, B. Ferrari, K.J. Wilkinson

J.-L. Loizeau, J. Dominik, Water Res. 41 (2007) 63.

[25] C. Gueguen, R. Gilbin, M. Pardos, J. Dominik, Appl. Geochem. 19

(2004) 153.

[26] D.L. Penry, P.A. Jumars, The American Naturalist 129 (1987)

69.

[27] J.-F. Pan, W.-X. Wang, Mar. Ecol. Prog. Ser. 276 (2004) 125.

[28] V. Croce, S. De Angelis, L. Patrolecco, S. Polesello, S. Valsecchi,

Environ. Toxicol. Chem. 24 (2005) 1165.

[29] M.C. Barber, Environ. Toxicol. Chem. 27 (2008) 755.

[30] O. Geffard, A. Geffard, A. Chaumont, B. Vollat, C. Alvarez, M.-H.

Tusseau-Vuillemin, J. Garric, Environ. Toxicol. Chem. 27 (2008)

1128.

[31] M.N. Moore, Environ. Int. 32 (2006) 967.

[32] N.M. Franklin, N.J. Roger, S.C. Apte, G.E. Batley, G.E. Gadd,

P.S. Casey, Environ. Sci. Technol. 41 (2007) 8484.

[33] E. Navarro, A. Baun, R. Behra, N.B. Hartmann, J. Filser, A.J. Miao,

A. Quigg, P.H. Santschi, L. Sigg, Ecotoxicology 17 (2008) 372.

[34] W.-X. Wang, N.S. Fisher, Limnol. Oceanogr. 41 (1996) 197.

[35] W.-X. Wang, N.S. Fisher, Environ. Toxicol. Chem. 18 (1999)

2034.

[36] J.F. McCarthy, L.W. Burrus, V.R. Tolbert, Arch. Environ. Contam.

Toxicol. 45 (2003) 364.

[37] L. Vigano, L. Patrolecco, S. Polesello, R. Pagnotta, Ecotoxicol.

Environ. Safety 69 (2008) 49.

[38] C. Pickhardt, C.L. Folt, C.Y. Chen, B. Klaue, J.D. Blum, Proc. Nat.

Acad. Sci. USA 99 (2002) 4419.








[39] R. Karimi, C.Y. Chen, P.C. Pickhardt, N. Fisher, C.L. Folt, Proc.

Nat. Acad. Sci. USA 104 (2007) 7477.

[40] S.N. Luoma, in: A. Tessier, D.R. Turner (Editors), Metal Speciation

and Bioavailability in Aquatic Systems, Wiley & Sons, Chichester,

UK, 1995, pp. 609–659.

[41] J.W. Chen, X.H. Li, H.Y. Yu, Y.N. Wang, X.L. Qiao, Sci. China Ser.

B 51 (2008) 593.

[42] H. Sanderson, M. Thomsen, Bull. Environ. Contam. Toxicol. 79

(2007) 79.

[43] M. Crane, G.A. Burton, J.M. Culp, M.S. Greenberg, K.R. Munkit-

trick, R. Ribeiro, M.H. Salazar, S.F. St-Jean, Integrated Environ.

Assess. Manage. 3 (2007) 234.

[44] A. Buffagni, S. Erba, M.T. Furse, Environ. Sci. Policy 10 (2007) 709.

[45] D. Hering, O. Moog, L. Sandin, P.F.M. Verdonschot, Hydrobiology

516 (2004) 1.

[46] L.S. McCarty, D. MacKay, Environ. Sci. Technol. 27 (1993) 1719.

[47] D.A.L. Vignati, B.J.D. Ferrari, J. Dominik, Environ. Sci. Technol.

41 (2007) 1067.

[48] J.P. Sumpter, A.C. Johnson, Environ. Sci. Technol 39 (2005)

4321.

[49] E.K. Duursma, J. Carroll, Environmental Compartments: Equilibria

and Assessment of Processes between Air, Water, Sediments and

Biota, Springer-Verlag, Berlin, Germany, 1996.

[50] J. Buffle, H.P. van Leeuwen (Editors), Environmental Particles,

Vol. 1, Lewis Publishers, Boca Raton, FL, USA, 1992.

[51] J.-L. Loizeau, D. Arbouille, S. Santiago, J.-P. Vernet, Sedimentol-

ogy 41 (1994) 353.

[52] P. Rosse, J.-L. Loizeau, Colloids Surf. A 217 (2003) 109.

[53] M. Baalousha, J.R. Lead, Environ. Sci. Technol. 41 (2007) 1111.

[54] C. Walther, S. Buchner, M. Filella, V. Chanudet, J. Colloids

Interface Sci. 301 (2006) 532.

[55] H. Etcheber, J.M. Jouanneau, Est. Coast. Mar. Sci. 11 (1980) 701.

[56] A.J. Horowitz, K.A. Elrick, R.C. Hooper, Hydrolog. Process. 2

(1989) 163.

[57] T.F. Rees, J.A. Leenheer, J.F. Ranville, Hydrolog. Process. 5 (1991)

201.

[58] E.D. Ongley, D.P. Blachford, Environ. Technol. Lett. 3 (1982) 219.

[59] J. Ingri, A. Winderlund, Geochim. Cosmochim. Acta 58 (1994)

5433.

[60] P. Rosse, D. Vignati, J. Dominik, Hydrolog. Process. 20 (2006)

2745.

[61] U. Forstner, Trends Anal. Chem. 23 (2004) 217.

[62] P. Lepom, A. Duffek, D16 Report on existing AQC tools and

validated methods; D19 Gaps Analysis for Validated Methods,

Deliverables EAQC-WISE Project, European Commission, Brussels,

Belgium, 2006, pp. 11.

[63] A.J. Horowitz, Environ. Sci. Technol. 20 (1986) 155.

[64] E.D. Goldberg, M. Baker, D.L. Fox, J. Mar. Res. 11 (1952) 194.

[65] A.J. Horowitz, K.R. Lum, J.R. Garbarino, G.E. Hall, C. Lemieux,

C.R. Demas, Environ. Sci. Technol. 30 (1996) 954.

[66] M.A. Morrison, G. Benoit, Environ. Sci. Technol. 35 (2001) 3774.

[67] M. Leermakers, W. Baeyens, P. Quevauviller, M. Horvat, Trends

Anal. Chem. 24 (2005) 383.

[68] D.H. Everett, Pure Appl. Chem. 31 (1971) 577.

[69] M. Taillefert, C.P. Lienemann, J.F. Gaillard, D. Perret, Geochim.

Cosmochim. Acta 64 (2000) 169.

[70] F.J. Doucet, L. Maguire, J.R. Lead, Anal. Chim. Acta 522 (2004)

59.

[71] L.J. Gimbert, P.M. Haygarth, R. Beckett, P.J. Worsfold, Environ.

Sci. Technol. 39 (2005) 1731.

[72] S. Liu, C. Carney, A. Hurwitz, J. Pharm. Pharmacol. 29 (1977)

319.

[73] M. Filella, J. Buffle, Colloids Surf. A 73 (1993) 255.

[74] Y.-W. Chen, J. Buffle, Water Res. 30 (1996) 2178.

[75] V. Chanudet, These 3950, Universite de Geneve, Switzerland,

2008.

[76] E.R. Unsworth, K.W. Warnken, H. Zhang, W. Davison, F. Black,

J. Buffle, J. Cao, R. Cleven, J. Galceran, P. Gunkel, E. Kalis, D. Kistler,

H.P. van Leeuwen, M. Martin, S. Noel, Y. Nur, N. Odzak, J. Puy,

W. van Riemsdijk, L. Sigg, E. Temminghoff, M.-L. Tercier-Waeber,

S. Toepperwien, R.M. Town, L. Weng, H. Xue, Environ. Sci. Technol.

40 (2006) 1942.

[77] D.A.L. Vignati, M. Camusso, J. Dominik, Ecol. Modell. 184 (2005)

125.

[78] A. Kot, B. Zabiegata, J. Namiesnik, Trends Anal. Chem. 19 (2000) 446.

[79] J. Buffle, M.-L. Tercier-Waeber, Trends Anal. Chem. 24 (2005)

172.

[80] K.A. Merritt, A. Amirbahman, Environ. Sci. Technol. 41 (2007)

717.

[81] O. Clarisse, H. Hintelmann, J. Environ. Monit. 8 (2006) 1242.

[82] R.P. Schwarzenbach, B.I. Escher, K. Fenner, T.B. Hofstetter,

C.A. Johnson, U. von Gunten, B. Wehrli, Science (Washington,

DC) 313 (2006) 1072.

[83] C.L. Babiarz, J. Hurley, S.R. Hoffmann, A.W. Andren, M.M. Shafer,

D. Armstrong, Environ. Sci. Technol. 35 (2001) 4773.

[84] D. Vignati, Terre & Environnement, 44, These 3477, Universite de

Geneve, Switzerland, 2004.

[85] K.J. Wilkinson, J.R. Lead (Editors), Environmental Colloids and

Particles: Behavior, Separation and Characterisation (Series on

Analytical and Physical Chemistry of Environmental Systems),

John Wiley and Sons, Chichester, UK, 2007.

[86] N.S. Wiggington, K.L. Haus, F. Hochella Jr., J. Environ. Monit. 9

(2007) 1306.

[87] J.R. Lead, W. Davison, J. Hamilton-Taylor, J. Buffle, Aquatic

Geochem. 3 (1997) 213.

[88] J.R. Lead, K.J. Wilkinson, Environ. Chem. 3 (2006) 159.



Pollutant partitioning for monitoring surface waters

Documents

Transcript of Pollutant partitioning for monitoring surface waters