environmental colloids and particles€¦ · in situ monitoring of aquatic systems vol. 6 (2000)...

Environmental Colloids and ParticlesBehaviour, Separation and Characterisation

IUPAC SERIES ON ANALYTICAL AND PHYSICAL CHEMISTRYOF ENVIRONMENTAL SYSTEMS

Series Editors

Jacques Buffle, University of Geneva, Geneva, SwitzerlandHerman P. van Leeuwen, Wageningen University, Wageningen, TheNetherlands

Series published within the framework of the activities of the IUPAC Commission onFundamental Environmental Chemistry, Division of Chemistry and the Environment.

INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY (IUPAC)Secretariat, PO Box 13757, 104 T. W. Alexander Drive, Building 19,Research Triangle Park, NC 27709-3757, USA

Previously published volumes (Lewis Publishers):Environmental Particles Vol. 1 (1992) ISBN 0-87371-589-6Edited by Jacques Buffle and Herman P. van LeeuwenEnvironmental Particles Vol. 2 (1993) ISBN 0-87371-895-XEdited by Jacques Buffle and Herman P. van Leeuwen

Previously Published volumes (John Wiley & Sons, Ltd):Metal Speciation and Bioavailability in Aquatic Systems Vol. 3 (1995)

ISBN 0-471-95830-1Edited by Andre Tessier and David R. TurnerStructure and Surface Reactions of Soil Particles Vol. 4 (1998)

ISBN 0-471-95936-7Edited by Pan M. Huang, Nicola Senesi and Jacques BuffleAtmospheric Particles Vol. 5 (1998)

ISBN 0-471-95935-9Edited by Roy M. Harrison and Rene van GriekenIn Situ Monitoring of Aquatic Systems Vol. 6 (2000)

ISBN 0-471-48979-4Edited by Jacques Buffle and George HorvaiThe Biogeochemistry of Iron in Seawater Vol. 7 (2001)

ISBN 0-471-49068-7Edited by David R. Turner and Keith A. HunterInteractions between Soil Particles and Microorganisms Vol. 8 (2002)

ISBN 0-471-60790-8Edited by Pan M. Huang, Jean-Marc Bollag and Nicola SenesiPhysicochemical Kinetics and Transport at Biointerfaces Vol. 9 (2004)

ISBN 0-471-49845-9Edited by Herman P. van Leeuwen and Wolfgang Koster

Forthcoming titles:Biophysical Chemistry of Fractal Structures and Processesin Environmental Systems Vol. 11 (2007)

ISBN 0-470-01474-1Edited by Nicola Senesi and Kevin J. Wilkinson

IUPAC Series on Analytical and Physical Chemistryof Environmental Systems. Volume 10

Environmental Colloidsand ParticlesBehaviour, Separation andCharacterisationEdited by

KEVIN J. WILKINSONUniversity of Montreal, Montreal, Canada

JAMIE R. LEADThe University of Birmingham, Birmingham, UK

John Wiley & Sons, Ltd

Copyright 2007 IUPAC

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Library of Congress Cataloging-in-Publication Data:

Wilkinson, Kevin J.Environmental colloids and particles : behaviour, separation, and

characterisation / Kevin J. Wilkinson, Jamie R. Lead.p. cm.

Includes indexISBN-13: 978-0-470-02432-4ISBN-10: 0-470-02432-1

1. Colloids. 2. Water chemistry. 3. Nanoparticles–Environmentalaspects. I Lead, Jamie R. II. Title.

QD549.W446 2006541′.345–dc22

2006020351

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN-13: 978-0-470-02432-4 (HB)ISBN-10: 0-470-02432-1 (HB)

Typeset in 10/12pt Times by Laserwords Private Limited, Chennai, IndiaPrinted and bound in Great Britain by Antony Rowe Ltd, Chippenham, WiltshireThis book is printed on acid-free paper responsibly manufactured from sustainable forestryin which at least two trees are planted for each one used for paper production.

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Contents

List of Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ixSeries Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

1 Environmental Colloids and Particles: Current Knowledge and FutureDevelopments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Jamie R. Lead and Kevin J. Wilkinson . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Colloidal Properties of Submicron Particles in Natural Waters . . . . . . . 17Montserrat Filella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Colloid–Trace Element Interactions in Aquatic Systems . . . . . . . . . . . . 95Frederic J. Doucet, Jamie R. Lead and Peter H. Santschi . . . . . . . . . . . . . .

4 Ultrafiltration and its Applications to Sampling and Characterisation ofAquatic Colloids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Laodong Guo and Peter H. Santschi . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Characterisation of Aquatic Colloids and Macromolecules by Field-flowFractionation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223Martin Hassellov, Frank von der Kammer and Ronald Beckett . . . . . . . . . .

6 Modern Electrophoretic Techniques for the Characterisation of NaturalOrganic Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277Philippe Schmitt-Kopplin and Jens Junkers . . . . . . . . . . . . . . . . . . . . . . .

7 Electrophoresis of Soft Colloids: Basic Principles and Applications . . . . . 315Jerome F. L. Duval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 Strategies and Advances in the Characterisation of EnvironmentalColloids by Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345Denis Mavrocordatos, Didier Perret and Gary G. Leppard . . . . . . . . . . . . .

9 Force Microscopy and Force Measurements of Environmental Colloids . . 405Eric Balnois, Georg Papastavrou, and Kevin J. Wilkinson . . . . . . . . . . . . .

10 Laser Scanning Microscopy for Microbial Flocs and Particles . . . . . . . . 469John R. Lawrence and Thomas R. Neu . . . . . . . . . . . . . . . . . . . . . . . . . .

11 Study of Environmental Systems by Means of Fluorescence CorrelationSpectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507Nicolas Fatin-Rouge and Jacques Buffle . . . . . . . . . . . . . . . . . . . . . . . . .

12 Laser-induced Breakdown Detection . . . . . . . . . . . . . . . . . . . . . . . . . . 555Jae-il Kim and Clemens Walther . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 Probing Environmental Colloids and Particles with X-rays . . . . . . . . . . 613Jean-Francois Gaillard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667

Kevin J. Wilkinson received a Ph.D. in Environmental Chem-istry from the National Water Research Institute of the Univer-sity of Quebec (INRS-Eau) in 1993. After his Ph.D., he joinedthe research group of Prof. Jacques Buffle at the Universityof Geneva, where he began to examine some of the importantbiophysical properties of environmental biopolymers and col-loids. Following the establishment of his own research groupin 1994, he focused his research on to relating the structure ofenvironmental colloids to their function in addition to initiat-ing a research programme designed to develop a fundamental

understanding of the chemical mechanisms of trace metal bioavailability. In 2005, he wasappointed Associate Professor of Chemistry at the University of Montreal. His teach-ing includes (bio)analytical and environmental chemistry. His current research interestsinclude: (i) improving our understanding of the role(s) of microorganisms on the bio-physicochemistry of trace elements and colloids; (ii) development and optimisation ofnovel analytical techniques for quantifying bioavailability and colloidal/aggregate struc-ture; (iii) characterising environmental biopolymers; and (iv) determining the role ofdiffusion in complex environmental media (biofilms, flocs, sediments). He is currentlya member of the editorial boards of Environmental Toxicology and Chemistry and Envi-ronmental Chemistry and a titular member of the IUPAC Chemistry and EnvironmentDivision.

Jamie R. Lead is an aquatic chemist who received his firstdegree in Environmental Science from the University of Sussex,U.K. He obtained his Ph.D. in 1994 from Lancaster University,U.K., investigating lanthanide and actinide speciation in relationto humic substances from aquatic and terrestrial systems.He subsequently undertook postdoctoral research at LancasterUniversity, working on colloid-metal interactions using field-flow fractionation, and at the University of Geneva, Switzerlandapplying fluorescence correlation spectroscopy to quantify thediffusion coefficients of organic colloids and nanoparticles. He

subsequently took up an academic position in the School of Geography, Earth andEnvironmental Sciences at the University of Birmingham, U.K. (2000), where he wasmade a Senior Lecturer in Water Chemistry (2004) and is currently a Reader in AquaticChemistry. His major current research interests are: (i) the development and applicationof new analytical and fractionation techniques in the area of metal speciation and colloidstructure; (ii) quantifying the structure of aquatic colloids and nanoparticles and therelationship structure has to their role in trace pollutant fate and behaviour; and (iii)the fate and behaviour of manufactured nanoparticles in the aquatic environment. He haspublished extensively in the area of colloid structure and the interactions of colloids withmetals. He heads a current knowledge transfer network on aquatic colloids (AQUANET)and on manufacture nanoparticles (NANONET), and as such, has organised and chairedseveral recent international conferences and workshops in these areas.

List of Contributors

Eric BalnoisLaboratoire Polymeres, Proprietes aux Interfaces et Composites (L2PIC), Universite deBretagne Sud, rue de St Maude, BP 92116, F-56321 Lorient Cedex, France

Ronald BeckettWater Studies Centre, School of Chemistry, Monash University (Clayton Campus),Melbourne, Victoria 3800, Australia

Jacques BuffleAnalytical and Biophysical Environmental Chemistry (CABE), Department of Inorganic,Analytical and Applied Chemistry, University of Geneva, 30 quai Ernest Ansermet,CH-1211 Geneva 4, Switzerland

Frederic J. DoucetUniversity of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK

Jerome F. L. DuvalEnvironment and Mineralogy Laboratory, UMR INPL-CNRS 7569, Research CenterFrancois Fiessinger, 15 avenue du Charmois, BP 40, F-54501 Vandoeuvre-les-Nancycedex, France

Nicolas Fatin-RougeLaboratoire de Chimie des Materiaux et Interfaces, 16 route de Gray, F-25030 Besanconcedex, France

Montserrat FilellaAnalytical and Biophysical Environmental Chemistry (CABE), Department of Inorganic,Analytical and Applied Chemistry, University of Geneva, 30 quai Ernest-Ansermet,CH-1211 Geneva 4, Switzerland

Jean-Francois GaillardDepartments of Civil and Environmental Engineering, Northwestern University, 2145Sheridan Road, Evanston, IL 60208-1309, USA

Laodong GuoDepartment of Marine Science, University of Southern Mississippi, 1020 BalchBoulevard, Stennis Space Center, MS 39529, USA

Martin HassellovDepartment of Chemistry, Goteborg University, S-412 96 Gothenburg, Sweden

Jens Junkers (deceased)GSF–National Research Center for Environment and Health, Institute for EcologicalChemistry, Molecular BioGeoanalysis, Ingolstadter Landstraße 1, D-85764 Neuherberg,Germany

x LIST OF CONTRIBUTORS

Jae-Il KimInstitut fur Nukleare Entsorgung, Forschungszentrum Karlsruhe, PO 3640, D-76021Karlsruhe, Germany

John R. LawrenceNational Water Research Institute, 11 Innovation Boulevard, Saskatoon, Saskatchewan,Canada, S7N 3H5

Jamie R. LeadDivision of Environmental Health and Risk Management, School of Geography, Earthand Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK

Gary G. LeppardNational Water Research Institute, 867 Lakeshore Road, PO Box 5050, Burlington,Ontario, Canada L7R 4A6

Denis Mavrocordatos (deceased)Swiss Federal Institute for Environmental Science and Technology, EAWAG Urban WaterManagement, 133 Uberlandstrasse, CH-8600 Dubendorf, Switzerland

Thomas R. NeuDepartment of River Ecology, UFZ Centre for Environmental Research Leipzig-Halle,Bruckstrasse 3a, D-39114 Magdeburg, Germany

Georg PapastavrouLaboratory of Colloid and Surface Chemistry (LCSC), Department of Inorganic,Analytical and Applied Chemistry, University of Geneva, Sciences II, 30 quai ErnestAnsermet, CH-1211 Geneva 4, Switzerland

Didier PerretSection of Chemistry, University of Geneva, 30 quai Ernest Ansermet, CH-1211 Geneva4, Switzerland

Peter H. SantschiDepartments of Marine Sciences and Oceanography, Laboratory for Oceanographic andEnvironmental Research, Texas A&M University at Galveston, 5007 Avenue U,Galveston, TX 77551, USA

Philippe Schmitt-KopplinGSF–National Research Center for Environment and Health, Institute for EcologicalChemistry, Molecular BioGeoanalysis, Ingolstadter Landstraße 1, D-85764 Neuherberg,Germany

Frank von der KammerInstitute for Geological Sciences, Environmental Geosciences, Vienna University, A-1090Vienna, Austria

Clemens WaltherInstitut fur Nukleare Entsorgung, Forschungszentrum Karlsruhe, PO 3640, D-76021Karlsruhe, Germany

Kevin J. WilkinsonDepartment of Chemistry, University of Montreal, CP 6128, Succ. centre-Ville, Montreal,Canada, H3C 3J7

Series Preface

The main purpose of the IUPAC Series on Analytical and Physical Chemistry of Environ-mental Systems is to make chemists, biologists, physicists and other scientists aware ofthe most important biophysicochemical conditions and processes that define the behaviourof environmental systems. The various volumes of the Series thus emphasise the funda-mental concepts of environmental processes, taking into account specific aspects such asphysical and chemical heterogeneity, and interaction with the biota. Another major goalof the series is to discuss the analytical tools that are available, or should be developed,to study these processes. Indeed, there still seems to be a great need for methodologydeveloped specifically for the field of analytical/physical chemistry of the environment.

This volume in the series focuses on the nature and properties of aquatic colloids and,in particular, the various recent instrumental techniques which can be used for their char-acterisation. It can be seen to follow the first two volumes of the series (EnvironmentalParticles, vols. 1 and 2, 1992–93). It is noteworthy that the techniques of surface, col-loid, polymer and gel characterisation, as well as the related scientific information thatthe techniques provide, have largely improved over the past 10–15 years. It is thus anopportune moment to perform a critical assessment of their capabilities for environmentalapplications.

This volume was realised within the framework of the activities of the IUPAC Divisionof Chemistry and the Environment. We thank IUPAC for its administrative and financialsupport and assistance with this project. With their help, it was possible to organize adiscussion meeting of the full team of chapter authors in Birmingham (U.K.) in 2004which was an essential step in the preparation and harmonisation of the various chaptersin this book.

The Series is well received and is growing prosperously. A new volume on the fractalproperties of soil particles will be published soon. As with all books in this series, it willpresent critical reviews reflecting the current state-of-the-art and provide guidelines forfuture research in the field.

Jacques Buffle and Herman P. van LeeuwenSeries Editors

Preface

In spite of decades of research, the precise role of colloids and nanoparticles in environ-mental systems is still poorly understood. For example, in soils and sediments, colloid-facilitated transport is a well-known, though rarely quantified, process. The bioavailabilityof pollutants is likely to be strongly modified by interactions with colloids, though fewstudies are able to discriminate between adsorption and the direct effects of the colloid onthe organism. Recent indications suggest that the introduction of engineered nanoparticlesinto the environment may be cause for concern due to their toxicity and potential abilityto influence contaminant and, perhaps, pathogen behaviour. Unfortunately, a majority ofresearch papers describe qualitatively or semi-quantitatively the above phenomena, usingparameters such as partition coefficients that cannot be generalised across environmen-tal media. In addition, although it is commonly accepted that the fate of trace elementsdepends to a large extent on their adsorption to colloidal phases, values of 0–100% bind-ing are typically reported. While such large variations can often be attributed to the traceelement that has been examined or the nature of the medium in which it occurred, alarge variability is often introduced by the analytical technique used to make the deter-mination and (unfortunately) the experience of the research group. Therefore, this bookwas written in order to (i) identify some of the common problems still needing study incolloid research (Chapter 1); (ii) summarise our current understanding of environmentalcolloids and their reactions (Chapters 2 and 3); and (iii) carefully and critically describe anumber of important techniques to characterise colloidal physical and chemical properties(Chapters 4–13). In this volume, the focus has been placed on modern and novel appli-cations of techniques that have not been previously examined in detail or on techniquesthat have seen vast methodological improvements over the past 10 years. Furthermore,as is often the case for colloidal researchers, the characterisation techniques have beenapproximately divided into those looking at whole samples (Chapters 4–7) and thoseexamining properties of a given sample fraction (Chapters 8–13).

This book is the result of the efforts of a number of authors, collaborators and stu-dents. It came about from the initiative of Professor D. Turner, following his organisationof a European research conference on aquatic colloids. The International Union of Pureand Applied Chemistry (IUPAC) then provided much of the structure and funding whichallowed this project to come to fruition. The role of the Series Editors, Professors H. P.van Leeuwen and J. Buffle is also greatly appreciated. In addition, the Technical Edi-tor, Professor R. M. Town, is acknowledged for her thoroughness and her extremelyimpressive turnaround times on each of the chapters. Finally, on a tragic note, we mustannounce that during the preparation of this book, two of our young chapter authors werelost prematurely. The contributions of Jens Junkers (Chapter 6) and Denis Mavrocordatos(Chapter 8) to their respective chapters were greatly appreciated. Their future contribu-tions to the characterisation of colloidal systems and to science, in general, will be greatlymissed. Both were young scientists who succeeded in leaving their mark in the field of

xiv PREFACE

environmental colloids, in spite of relatively short careers. Both left behind numerousfriends, colleagues and family who will miss them greatly.

Jens Junkers Denis Mavrocordatos(1970–2004) (1968–2003)

K. J. Wilkinson and J. R. Lead

1 Environmental Colloids and Particles:Current Knowledge and FutureDevelopments

JAMIE R. LEAD

Division of Environmental Health and Risk Management, School of Geography, Earth andEnvironmental Sciences, University of Birmingham, Birmingham B15 2TT, UK

KEVIN J. WILKINSON

Department of Chemistry, University of Montreal, P.O. Box 6128, Succ. Centre-ville,Montreal, Canada H3C 3J7

1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 The Importance of Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Non-size-based measurements of colloids and particles . . . . . . . . . . . . . . . . 94 Strategies for advancing our understanding of colloidal systems . . . . . . . . . . 105 Future perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1 DEFINITIONS

The precise definition of environmental colloids or environmental colloidal systems wasdiscussed in the first volume of this series [1], but still remains a matter of some debate,years later. In a number of areas, including environmental chemistry, the idea of phase hasbeen excluded from common usage and we now often talk of colloids rather than colloidalsystems. This procedure will be followed here, but it should be remembered that environ-mental colloids are relatively dilute dispersions of solid (sometimes liquid or gas) phaseswithin a water or atmospheric gas phase. Although a great deal of discussion revolvesaround the exact meanings of the terms ‘colloids’ and ‘particles’, to some extent, theseproblems are trivial, in that they primarily relate to nomenclature differences amongst dif-ferent disciplines and different researchers that could be avoided by the careful and system-atic use of appropriate terms. For instance, a size-based definition was first developed inthe field of colloid chemistry [2], however, water engineers frequently use membrane fil-ters with nominal pore sizes of about 5–10 µm, while aquatic chemists commonly use 0.2or 0.45 µm pore sizes. Even within the broadly defined environmental sciences, differentdefinitions are employed. For example, membranes with a ca., 1 nm (1 kDa) nominal pore

Environmental Colloids and Particles. Edited by K. J. Wilkinson and J. R. Lead 2007 IUPAC

2 CURRENT KNOWLEDGE AND FUTURE DEVELOPMENTS

size are often used to discriminate, somewhat arbitrarily, between the truly dissolvedand the non-aqueous phases. Finally, further confusion has recently occurred due to thenow common use of terms such as macromolecules and nanoparticles. Generally, macro-molecule refers to a small polymeric colloid while the term nanoparticle is also appliedto the very smallest colloids [3], usually below 100 nm.

In this chapter and throughout the book, the lower size limit for colloids is set in asimilar manner to traditional colloid chemistry, i.e., any organic or inorganic entity largeenough to have a supramolecular structure and properties that differ markedly from thoseof the aqueous phase alone, e.g., possibility of conformational changes or the develop-ment of an electrical surface field. This limit coincides with the environmentally relevantcondition that aquatic colloids are generally small enough that, in the absence of aggrega-tion, Brownian motion is sufficient to keep them suspended in the water column for longperiods (>hours–days). Similarly, the upper size limit corresponds to the point whereinterfacial phenomena are qualitatively less important due to the smaller relative surfaceto volume ratio of the colloid/particle, although interfacial phenomena are important inall environmental systems. From the preceding constraints has evolved the more practicalIUPAC definition that the colloidal size range will typically have at least one dimensionin the 1 nm to 1 µm size range [1,4], while particles are defined as materials whosedimensions are >1 µm.

Clearly, there are limitations on the usefulness of these definitions, for both practicaland theoretical reasons. Due to both the chemical and physical complexity of environmen-tal colloids and particles and a lack of standardisation of analytical techniques, includingfractionation and sizing methods (especially filtration [5]), experimental data can rarelybe rigorously related to even the operational IUPAC definitions. For example, it is not yetpossible to determine direct, systematic and rigorous relationships between the physico-chemical properties of membrane permeates or retentates and their environmental function.The current size-based definitions are essentially operational; greater understanding maybe gained from definitions that are based on colloidal structure or function (environ-mental role), in an analogous manner to biological macromolecules. Unfortunately, it isnot yet clear that any such attempt would be successful, again due to the complexity ofenvironmental colloids and particles.

Nevertheless, the search for more fundamental definitions of colloids is in progress [6].For example, it has been argued that colloids should be defined as those species for whichno chemical potential can be defined [7]. In a view that was developed further by Gustafs-son and Gschwend [6], Buffle and Leppard considered that colloids were dominated byaggregation processes whereas particles were dominated by sedimentation [8]. Accordingto Gustafsson and Gschwend, a colloid in one water body could behave as a particlein another water body, depending on the precise physicochemistry of the medium. Thisimplies that the distinction between colloids and particles may be both site and time spe-cific. Gustafsson and Gschwend [6] distinguished the colloidal from the dissolved phaseby the presence or absence of an internal milieu with properties, such as a dielectricconstant, that are substantially different from those of the bulk solution. In such a case, apolyelectrolyte with no internal spaces could be considered as being a dissolved species,although this view has been challenged [9]. Clearly, the requirement for an internal milieuposes some problems and neglects the importance of the surface binding of pollutants.

J. R. LEAD AND K. J. WILKINSON 3

Although these definitions are relatively comprehensive, it must be recognised thatthey are limited when applied to the environment. For example, sedimentation is surelyof less importance in groundwaters than it is in surface waters. Second, as noted above,the surface properties of colloids and particles are extremely important. Third, colloidsare not at equilibrium but rather exist as a dynamic system with respect to aggregationprocesses, pollutant binding and biological uptake. Finally, even if the conceptual modelsprovide a good starting point for further understanding the role and impact of colloids andparticles, it is currently extremely difficult to validate the models with rigorous analyticalresults. Despite important progress over the past few decades of research, we are only atthe very beginnings of a comprehensive understanding in this field.

2 THE IMPORTANCE OF SIZE

As mentioned above, between 1 nm and 1 µm, solid-phase materials are dominated bysurface properties, including surface area and electrical charge, rather than bulk propertiessuch as the chemical composition of the colloids. Interfacial properties are particularlyimportant at the lower end of the size scale. For example, about 50% of the mass (oratoms) is found at the surface of a 3 nm colloid compared with about 5% of the massfor a 30 nm colloid [3]. Colloidal surface properties are therefore extremely important tounderstanding environmental function since colloidal aggregation and the sorption of tracepollutants, nutrients and pathogens are dependent on the nature of the colloid–colloid andcolloid–water interfaces [10–12]. At the upper end of the colloidal size scale (ca. 1 µm),not only do surface properties become less relevant, but also gravitational forces beginto exceed forces due to Brownian motion, with a resulting sedimentation of the parti-cles/aggregates [13].

Historically, filtration through a 0.45 µm filter has been used to distinguish the par-ticulate and dissolved phases. The filtration step has also been used to reduce samplecomplexity, partially to sterilise the dissolved phase through removal of a majority of themicroorganisms and to improve analytical sensitivity, e.g. by reducing fouling on electrodeor other surfaces. More recently, additional filtration steps have been introduced [5,14]such that filtration is now typically performed with several nominal pore sizes in orderto define dissolved, colloidal and particulate phases. Nevertheless, it must be emphasisedthat these phases are purely operational and are not necessarily related to real differencesin structure or to environmental or chemical behaviour. In addition, quantitative compar-isons between data sets are difficult due to a variability in the nominal pore sizes that areused and to artefacts that are inherent in the filtration method [4,15–17]. Nonetheless,filtration has produced a wealth of data and greatly advanced our understanding of envi-ronmental colloids and particles. However, as stressed later in this volume, confidence infiltration and ultrafiltration data requires that rigorous protocols are implemented, includ-ing calculation of mass balances and quantification of the particle size distributions inthe sample, retentate and permeate using appropriate microscopic techniques. These ver-ifications are rarely performed and therefore a large proportion of literature data must becritically re-evaluated.

Very little is known, in detail and with accuracy, about the true size distribution ofnaturally occurring colloids and particles, either as isolated entities or as aggregates, inany environmental compartment. A simplified size distribution of several key biological,organic and mineral phases is given in Figure 1. A key observation from this figure is


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electron microscopyatomic force microscopy

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light scattering

LIBD

x-ray absorption x-ray, neutron scattering

Figure 1. Size distributions of various types of environmental colloids and particlesand several of the analytical techniques that are used to characterize them. Abbrevia-tions: FFF = field-flow fractionation (Chapter 5); FCS = fluorescence correlation spectroscopy(Chapter 11); LIBD = laser-induced breakdown spectroscopy (Chapter 12). Adapted from [1] withpermission from Taylor and Francis

that the sizes of each of the apparently homogeneous colloid types are often spread overseveral orders of magnitude. Furthermore, the categorisation of different colloid types issomewhat artificial since, in natural systems, colloid groups are rarely found in purifiedforms but most often are components of complex heteroaggregates. Even a ‘homogeneous’colloid class such as the humic substances are better described as a complex mixture thatincludes recognisable biomolecules [18]. Figure 1 also indicates the approximate sizeranges in which several of the key colloidal characterisation techniques operate.

Several examples of some colloidal and particulate size distributions, measured usingdifferent techniques on unperturbed natural waters, are given in Figure 2. Interestingly,


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Figure 2. Particle size distributions calculated from AFM, ESEM, SEM [15] and SdFFF [19].Parts (a)–(c) from Journal of Environmental Monitoring, 2005, 7, 115–121. Reproduced by per-mission of The Royal Society of Chemistry


observed sizes are often distributed roughly normally (usually skewed with a long tail)within the analytical window of the technique being employed [15], strongly suggestingan important limitation of the individual techniques and the need to use several character-isation techniques simultaneously, a theme which we will return to later in this chapter.Indeed, Figure 3 shows comparative images using scanning electron microscopy (SEM)and environmental scanning electron microscopy (ESEM) of the same sample with consid-erably different observed morphologies. The variability of the distributions demonstratesboth the difficulty of producing reliable data and the fundamentally different nature ofdata collected by different techniques. Nevertheless, this situation allows a number oftechniques to be applied to produce representative data on the nature of colloids and theirinteractions.

Although average measures are most often quantified, environmental colloids are alwayspolydisperse, often with undefined size distributions. Size distributions can be determinedexperimentally by field-flow fractionation (FFF) [21,22], electron microscopy [15,23,24]and atomic force microscopy (AFM) [15,25,26] and calculated from fluorescence corre-lation spectroscopy (FCS) [27–29] and dynamic light scattering [30]. Nevertheless, thetechniques each have different detection limits and detection windows correspondingto different size ranges (Figure 1). Some techniques are simply incapable of measur-ing accurately the whole range of data on polydisperse samples, a factor which mayboth skew the data collected and invalidate their interpretation. In addition, size distri-butions may be related to the mass, number or surface area of the colloids as describedby the number-, weight- or z-averages (Table 1). Unfortunately, a large proportion ofliterature values do not specify which average is determined, in spite of the fact thatfor polydisperse samples, the different averages will have very different numerical val-ues (Figure 4). Furthermore, most of the colloidal sizing techniques do not measuresize directly but rather a different physicochemical property from which the size isderived. For example, whereas physical (number-average) dimensions are determined bymicroscopic techniques [15,24], diffusion coefficients are generally determined from lightscattering, size-exclusion chromatography, flow field-flow fractionation (FlFFF) [21,28]and FCS [27,29]. Charge/size ratios are derived from electrophoretic mobilities [31] andbuoyant mass from sedimentation FFF [21] and other centrifugation-based techniques suchas analytical ultracentrifugation. Although molecular dimensions and molar masses canbe estimated from diffusion coefficients (and eventually electrophoretic mobilities whencoupled to titration data), the calculations are based on a large number of (sometimesunwarranted) assumptions (sphericity, permeability, homogeneous charge distribution,absence of aggregates, etc.) [32]. Although each of the above points refers to currentand important problems, they will be discussed but not solved in this volume; futuregood-quality science will need to meet these challenges in appropriate ways.

Consequently, numerous, largely unsupported, assumptions have often been acceptedby the environmental sciences community. For instance, the importance of colloids isoften ascribed to an increase in specific surface area with decreasing size resulting in theexposure of a greater number of functional groups at the solid–aqueous interface andthus a greater uptake of trace pollutants. Furthermore, sizes are generally held to fol-low a Pareto or other (e.g. log-normal [33]) distribution (Figure 2). However, the actualhigh-quality experimental data to support these beliefs (in particular those employing


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Figure 3. Images of the Tamar Estuary taken by both SEM (a, c, e, g) and ESEM (b, d, f, h) [20].The images are taken from water from the same sample bottle, but a–b, c–d, e–f and g–h arenot image pairs of exactly the same sample. Reprinted from Doucet, F. J., Maguire, L. and Lead,J. R., Size fractionation of aquatic colloids and particles by cross-flow filtration, analysis by scan-ning electron and atomic force microscopy, Analytica Chimica Acta, 522, 59–71, Copyright 2004,with permission from Elsevier

several different techniques) are extremely small. In addition, it is highly likely thatmany types of environmental colloids are permeable to both water [34] and trace pol-lutants so that simply taking into account surface complexation reactions would resultin an underestimation of colloidal binding. Indeed, following their adsorption on thesurface of the colloidal particle, it is likely, in many cases, that pollutants are takenup into the body of the colloid or particle [35]. A final related point is that very fewstudies have been performed in situ: most results have been extrapolated from partially


Table 1. Equations for number-, weight- and z-average molar masses and diameters. Severaltechniques allow for the near direct determination of these average values (e.g. electron or trans-mission electron microscopy: number-average diameters; fluorescence correlation spectroscopy:number-(single fluorophore) or weight-(several fluorophores) average diameters; dynamic lightscattering a : z-average diameters). For monodisperse samples (Mw/Mn ≈ 1), average values willbe similar for all of the calculations whereas for a typical polydisperse sample values can vary byseveral orders of magnitude (cf. Figure 4)

Number-average Weight-average b z-Average

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=∑

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a Dynamic light scattering calculates the z-average diameter for Rayleigh scatterers (d � λ) and for particleswhere measurements have been extrapolated to a scattering angle of 0.b Calculations of diameter averages assume that nid

3 is proportional to the weight of the particles through thedensity and that the density is constant for all size ranges.

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ion

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Figure 4. Number-(solid line), weight-(dashed line) and z-average (dotted line) diameters calcu-lated from the AFM colloidal size (heights) distribution given in Figure 2a using the equationsprovided in Table 1. In this case of a natural, polydisperse sample, the number-average meanwas calculated as 12.2 nm, the weight-average diameter as 58.5 nm and the z-average diameteras 75.8 nm. The example illustrates that even for the same sample, techniques that are based ondifferent principles will provide a substantially different indication of the particle size distributions.In addition, the analytical bias of the technique (e.g. detection window, Figure 1) will significantlyinfluence what is recorded by the scientist. To facilitate comparison, data have been smoothed usinga negative exponential

processed or model systems under controlled laboratory conditions. In order to overcomesome of the major difficulties that remain in this field, adequate and reliable methodsfor sampling, sample handling, fractionation, analysis and modelling will need to bedeveloped.


Finally, when considering the size of a colloid or particle of particular shape, it isessential to ask two questions. First, why are the size-based measurements being per-formed, i.e. what does this analysis reveal about environmental processes such as traceelement uptake to biota? Second, are there ways of performing more revealing analyses?The first question is idealistic and forces us to consider the link between size and the rele-vant processes. There is no doubt that size is a useful parameter for considering colloidalbehaviour. It affects processes such as the transport and biouptake of trace pollutantsin sediments, soils, waters and the atmosphere. Furthermore, colloidal size is a standardparameter that can, with reservations, be used to compare data sets. Nevertheless, thereliance on size as a primary measurement is limiting, as discussed in the next section.The second question is more practical. More revealing parameters can indeed be mea-sured. A significant current challenge in the study of environmental colloids and particlesis to develop these methods and to apply them in order to produce non-trivial results thatare based on parameters other than size.

3 NON-SIZE-BASED MEASUREMENTS OF COLLOIDS AND PARTICLES

Although size is a useful and frequently measured parameter, it is limited in the extentto which it can be used to gain detailed understanding of environmental behaviour. Forinstance, larger particles often dominate the sedimentation process. Since the larger par-ticles generally, but not always [36,37], dominate particle mass distributions [1], a massdistribution may be the most relevant means to present sedimentation data. In contrast,insight into aggregation processes will likely benefit more from considering particle num-ber distributions, which are likely to be dominated by the smaller colloids. Finally, surfacearea may be the most relevant parameter when considering pollutant uptake by colloidsand particles. Like particle number, surface area is likely to be dominated by smallercolloids, albeit not in an identical manner. Since these three processes, i.e. uptake, aggre-gation and sedimentation, are interrelated, e.g. through the colloidal pumping model [38],a thorough understanding of the entire process will likely require accurate determinationsof the mass, number and specific surface area distributions.

For a number of processes, size can be considered as a proxy for other parameters. Inparticular, knowledge of the diffusion coefficients of colloidal complexes with trace ele-ments and organic pollutants is vital to understanding: (i) their transport in soils, sedimentsand the diffusive boundary layer around surfaces; (ii) their mass transport to biologicalorganisms [39] and (iii) their quantitative analytical determination using important in situmetal speciation techniques such as diffusive gradients in thin films (DGT) and voltamme-try. Although a number of techniques measure colloidal diffusion coefficients (Table 2),data are most often converted to size, as in the case of FlFFF [21,22,40] by assumingthat the colloids are impermeable and spherical (Stokes–Einstein equation). Clearly, innatural systems, there is a range of colloidal morphologies, many of extreme complexity.Although the conversion to equivalent radii is helpful for making comparisons, diffusioncoefficients are arguably a more powerful indicator of colloidal activity (aggregation,reactivity, etc.) and should be retained, whenever possible. In addition, other parameterssuch as fractal dimensions (aggregates) [41,42], colloidal form factors [24], gyration radiior contour or persistence lengths (e.g. fibrils) [43] may also provide structural informa-tion that is more easily related to environmental function. Similar arguments are valid


Table 2. Comparison of most probable (mean or median) diffusion coefficients (m2s−1 × 1010) forthe Suwannee River standard fulvic acid. Figures in parentheses are standard deviations. For FCS,poor accuracy was obtained at high ionic strength (n = 3); for FlFFF, no values were measurableat low pH and high ionic strength (n = 3); for PFG NMR, data for regions 1–4 (correspondingto 0.8–1.9, 1.9–3.5, 3.5–4.3, 6.3–8.1 ppm) have been collapsed to give the most probable dif-fusion coefficients. For PFG-NMR, standard deviations for all individual data in all cases were0.2. Reprinted with permission from Environmental Science and Technology, 34, 3508–33513.Copyright 2000 American Chemical Society

pH or pD

Ionic strength/mmol dm−3 4 5.5 7.0

FCS 5 2.21 (0.07) 2.52 (0.02) 2.71 (0.06)50 2.05 (0.02) 2.40 (0.04) 2.61 (0.04)500 2–3 2–3 2–3

FlFFF 5 – 3.0 (0.08) 2.9 (0.03)50 – 1.9 (0.05) 2.2 (0.02)500 –

PFG-NMR Low 2.8–3.6 2.5–3.7 2.4–3.5500 2.6–3.8 2.5–3.7 2.5–3.5

for other colloidal characterisation techniques such as electrophoresis [34], which pro-vides an estimate of the charge/size ratio of the colloids [34,44], although conversions ofelectrophoretic mobilities often require significant and complex interpretation [45].

4 STRATEGIES FOR ADVANCING OUR UNDERSTANDING OFCOLLOIDAL SYSTEMS

Based on the above considerations, it is clear that to enhance further our understand-ing of environmental colloids and their impacts, there is a need to (i) employ in situmethods [46]; (ii) use non-perturbing methods [7]; (iii) use a variety of methods forcomparative purposes [23,27,28,47]; and (iv) take great care in sampling and sampleprocessing and use appropriate checks including the measurement of standard materials,where appropriate [48]. The use of standard materials is discussed in Chapter 3 in relationto ultrafiltration and cross-flow filtration (CFF) techniques, but is nevertheless a continuinglimitation in the nanoparticle range where few appropriate standards are available [24,25].The simultaneous use of a number of methods is another key point. Indeed, a numberof studies have demonstrated that a reliance on any single technique may introduce sub-stantial distortions of our view of the colloidal structure [15,28,33,36,47] and their effectson pollutant uptake [10]. When analysing the same colloidal sample, agreement betweenseveral techniques will provide increased confidence in the result [28] while disagreementwill require the differences to be rationalised appropriately. This type of comparison canalso mitigate the analytical uncertainties that normally occur when analysing unknownsamples in the absence of certified reference materials.

An example that demonstrates the importance of using several techniques in parallelis given in Table 2. For diffusion coefficients of the reasonably monodisperse and puri-fied Suwannee River standard fulvic acid, good agreement was obtained by FCS, nuclearmagnetic resonance (NMR) and FlFFF [28]. In contrast, some multi-method studies to


evaluate colloidal properties have shown only partial agreement (and indeed often substan-tial differences) in size distributions, metal binding properties and colloidal morphologies,especially for natural samples {e.g. AFM, transmission electron microscopy (TEM) andFCS [49]; AFM and ESEM [15]; AFM and TEM [47]; and CFF and FlFFF [10]}. Inaddition to the size distributions provided in Figure 2, comparative SEM and ESEMimages obtained from a single sampling from a freshwater sample are given in Figure 4.Substantially different conformations and surface coverages are shown. Similarly, for thesame site, AFM images [15] were very different from EM images. Interestingly, TEMand AFM images were generally more similar [47] than images from AFM and ESEM,even though the experimental conditions were nearly identical for the AFM and ESEMacquisition (i.e. relative humidity of ca. 50–60%). Although TEM images are generallyobtained under high vacuum, the use of hydrophilic resins and multi-method TEM samplepreparation techniques [24] may be sufficient to stabilise the three-dimensional structureof the colloids and colloidal aggregates [23]. In a final example that clearly demon-strates the complementary nature of three colloidal characterisation techniques, intrinsicviscosity measurements convincingly demonstrated an increase in the diameter of humicsubstances with increasing pH [50] whereas FCS demonstrated the opposite trend [28] andAFM height measurements showed no trend [26]. In this case, the differences occurredbecause each of the techniques probed different parameters. The story of the blind mentrying to define an elephant by touch may be useful here. One man finds the tail andthinks it is a snake, another finds a leg and thinks it is a tree and so on. Similarly, in theabove example, the intrinsic viscosity measurements evaluated molecular volumes (butignored aggregates) whereas FCS measured an average diffusion coefficient that takesinto account the effect of aggregation in solution. The AFM measurements evaluatedadsorbed (molecular or aggregate) heights following interaction with a substrate (andpossible reorganisation at the solid–water interface).

Clearly, the analytical uncertainty associated with multi-method measurements of nat-ural systems is increased because it is difficult to know a priori whether the analyses areincorrect or rather whether different aspects of the same structure have been revealed.The development of certified reference materials, although difficult due to colloidal com-plexity and instability, may nonetheless be helpful for checking instrument operation.In addition, relevant materials, including synthetic manganese or iron oxides, standardhumic substances (HS; e.g. International Humic Substances Society standards) or micro-bial exudates are being used more often and with greater success. Future research willtherefore require the investigation of ‘standard’ or reference colloids in addition to mini-mally perturbed colloids from real systems.

5 FUTURE PERSPECTIVES

Over the past 15 years, enormous progress has been made towards an understandingof environmental colloidal systems, including the development and application of frac-tionation and analysis techniques; the development of models; the elucidation of colloidalstructure and their interaction with trace elements, nutrients and pathogens; and the impactof colloids on the fate and behaviour of the trace elements, nutrients and pathogens.

The development of powerful techniques by which colloids and particles can be frac-tionated and analysed has been the primary, unambiguous improvement of recent years.


As detailed in the chapters that follow, the (continuing) development and optimisationof novel, minimally perturbing (ideally in situ) methods has immensely improved ourability to quantify colloidal and particulate structures and their behaviour in the environ-ment. In addition, sophisticated models for quantifying colloidal structure and predictingpollutant binding to colloids and colloidal transport have been developed. Nevertheless,further improvements are still required before the majority of models can be used withconfidence in the real environment. Hence the iterative development and application oftechniques and models to real systems is a key future development. Further discussionof this point is found in each of the individual chapters, although it should be noted thatmany of the most recent methods have only rarely been used on unperturbed colloidalenvironmental samples.

Significant developments into the analysis of colloidal structure and their impact onpollutant, nutrient and pathogen fate and behaviour have occurred in the last 15 years,although this field is also still at an early stage. Many of the colloidal characterisa-tion techniques (AFM, ESEM, FCS, CE, FFF, etc.) have not been fully or appropriatelydeployed in the environment and therefore our current understanding of natural col-loidal structures is tentative and only partially quantitative. Significant improvementsare expected over the next 15 years once we are better able to couple the nanoscopiccharacterisation obtained by using FlFFF, AFM, TEM and other methods with concep-tual models of colloid structure and their interactions. A more systematic determinationof parameters, such as diffusion coefficients and fractal dimensions, will also be usefulto gain greater understanding at a fundamental, mechanistic and quantitative level. Ourunderstanding of colloidal systems has greatly evolved since the production of the firstvolume of Environmental Particles [1], 15 years ago. The next 15 years are certain tobe extremely promising with exciting developments of fundamental knowledge in thisvital area.

REFERENCES

1. Buffle, J. and van Leeuwen, H. P., eds (1992). Environmental Particles. IUPAC Series onAnalytical and Physical Chemistry of Environmental Systems, Vol. 1. Lewis, Boca Raton,FL.

2. Goodwin, J. (2004). Colloids and Interfaces with Surfactants and Polymers. John Wiley &Sons, Ltd, Chichester.

3. Dowling, A. (2005). Nanoscience and Nanotechnologies: Opportunities and Uncertainties.Royal Society/Royal Academy of Engineering, London.

4. Lead, J. R., Davison, W., Hamilton-Taylor, J. and Buffle, J. (1997). Characterizing colloidalmaterial in natural waters Aquat. Geochem., 3, 213–232.

5. Guo, L. and Santschi, P. H. (2006). Ultrafiltration and its application to sampling and Charac-terisation of aquatic colloids. In Environmental Colloids and Particles: Behaviour, Structureand Characterisation, eds Wilkinson, K. J. and Lead, J. R. IUPAC Series on Analytical andPhysical Chemistry of Environmental Systems, Vol. 10. John Wiley & Sons, Ltd, Chichester,Chapter 4.

6. Gustafsson, O. and Gschwend, P. M. (1997). Aquatic colloids: concepts, definitions, andcurrent challenges, Limnol. Oceanogr., 42, 519–528.

7. Stumm, W. (1993). Aquatic colloids as Chemical reactants: surface structure and reactivity,Colloids Surf. A, 73, 1–18.

8. Buffle, J. and Leppard, G. G. (1995). Characterization of aquatic colloids and macromolecules:Part I. Structure and behaviour of colloidal material, Environ. Sci. Technol., 29, 2169–2175.


9. Doucet, F. J., Lead, J. R. and Santschi, P. H. (2006). Colloids–trace element interactions inaquatic systems. In Environmental Colloids: Behaviour, Structure and Characterisation, edsWilkinson, K. J. and Lead, J. R. IUPAC Series on Analytical and Physical Chemistry ofEnvironmental Systems, Vol. 10. John Wiley & Sons, Ltd, Chichester, Chapter 3.

10. Benedetti, M. F., Ranville, J. F., Allard, T. and Bednar, A. J. (2003). The iron status incolloidal matter from the Rio Negro, Brazil, Colloids. Surf. A, 217, 1–9.

11. Foster, A. L., Brown, G. E. and Parks, G. A. (2003). X-ray absorption fine structure study ofAs(V) and Se(IV) sorption complexes on hydrous Mn oxides, Geochim. Cosmochim. Acta,67, 1937–1953.

12. Campbell, P. G. C., Twiss, M. R. and Wilkinson, K. J. (1997). Accumulation of naturalorganic matter on the surfaces of living cells: implications for the interaction of toxic soluteswith aquatic biota, Can. J. Fish. Aquat. Sci., 54, 2543–2554.

13. Gustafsson, O., Duker, A., Larsson, J., Andersson, P. and Ingri, J. (2000). Functional sep-aration of colloids and gravitoids in surface waters based on differential settling velocity:coupled cross-flow filtration–split flow thin-cell fractionation (Cff-Splitt), Limnol. Oceanogr.,48, 1731–1742.

14. Heathwaite, L., Haygarth, P., Matthews, R., Preedy, N. and Butler, P. (2005). Evaluatingcolloidal phosphorus delivery to surface waters from diffuse agricultural sources, J. Environ.Qual., 34, 287–298.

15. Doucet, F. J., Maguire, L. and Lead, J. R. (2004). Size fractionation of aquatic colloids andparticles by cross flow filtration: analysis by scanning electron and atomic force microscopy,Anal. Chim. Acta, 522, 59–71.

16. Horowitz, A. J., Lum, K. R., Garbarino, J. R., Hall, G. E., Lemieux, C. and Demas, C. R.(1996). Problems associated with using filtration to define dissolved trace element concentra-tions in natural water samples, Environ. Sci. Technol. 30, 954–963.

17. Buffle, J., Perret, D. and Newman, M. (1992). The use of filtration and ultrafiltration for sizefractionation of aquatic particles. In Environmental Particles, Vol. 1, eds Buffle, J. and vanLeeuwen, H. P. Lewis, Boca Raton, FL, p. 554.

18. Sutton, R. and Sposito, G. (2005). Molecular structure in soil humic substances: the new view,Environ. Sci. Technol., 39, 9009–9015.

19. Gimbert, L. J., Haygarth, P. M., Beckett, R. and Worsfold, P. J. (2005). Comparison of cen-trifugation and filtration techniques for the size fractionation of colloidal material in soil sus-pensions using sedimentation field-flow fractionation, Environ. Sci. Technol., 39, 1731–1735.

20. Doucet, F. J., Lead, J. R., Maguire, L., Achterberg, E. and Millward, G. (2005). Visualisationof natural aquatic colloids and particles – a comparison of conventional high vacuum SEMand environmental scanning electron microscopy, J. Environ. Monit., 7, 115–121.

21. Hassellov, M., von der Kammer, F. and Beckett, R. (2006). Characterisation of aquatic col-loids in macromolecules by field-flow fractionation. In Environmental Colloids: Behaviour,Structure and Characterization, eds Wilkinson, K. J. and Lead, J. R. IUPAC Series on Ana-lytical and Physical Chemistry of Environmental Systems, Vol. 10. John Wiley & Sons, Ltd,Chichester, Chapter 5.

22. Lyven, B., Hassellov, M., Turner, D. R., Haraldsson, C. and Andersson, K. (2003). Compe-tition between iron- and carbon-based carriers for trace metals in a freshwater assessed usingflow field-flow fractionation coupled to ICP-MS, Geochim. Cosmochim. Acta, 67, 3791–3802.

23. Liss, S. N., Droppo, I. G., Flanagan, S. T. and Leppard, G. G. (1996). Floc architecture inwastewater and natural riverine systems, Environ. Sci. Technol., 30, 680–686.

24. Mavrocordatos, D., Perret, D. and Leppard, G. G. (2007). Strategies and advances in thecharacterisation of environmental colloids by electron microscopy. In Environmental Colloids:Behaviour, Structure and Characterisation, eds Wilkinson, K. J. and Lead, J. R., IUPAC Serieson Analytical and Physical Chemistry of Environmental Systems, Vol. 10. John Wiley & SonsLtd, Chichester, Chapter 8.

25. Balnois, E., Papastavrou, G. and Wilkinson, K. J. (2006). Force microscopy and force mea-surements of environmental colloids. In Environmental Colloids: Behaviour, Structure andCharacterisation, eds Wilkinson, K. J. and Lead, J. R. IUPAC Series on Analytical andPhysical Chemistry of Environmental Systems, Vol. 10. John Wiley & Sons, Ltd, Chichester,Chapter 9.


26. Balnois, E., Wilkinson, K. J., Lead, J. R. and Buffle, J. (1999). Atomic force microscopy ofhumic substances: effects of pH and ionic strength, Environ. Sci. Technol., 33, 1311–1317.

27. Lead, J. R., Wilkinson, K. J. and Starchev, K. (2003). Diffusion coefficients of humic sub-stances in agarose gel and in water, Environ. Sci. Technol., 37, 482–487.

28. Lead., J. R., Wilkinson, K. J., Balnois, E., Cutak, B., Larive, C., Assemi, S. and Beckett,R. (2000). Diffusion coefficients and polydispersities of the Suwannee River fulvic acid:comparison of fluorescence correlation spectroscopy, pulsed-field gradient nuclear magneticresonance and flow field-flow fractionation, Environ. Sci. Technol., 34, 3508–3513.

29. Fatin-Rouge, N. and Buffle, J. (2007). Study of environmental systems by means of fluores-cence correlation spectroscopy. In Environmental Colloids and Particles: Behaviour, Structureand Characterisation, eds Wilkinson, K. J. and Lead, J. R. IUPAC Series on Analytical andPhysical Chemistry of Environmental Systems, Vol. 10. John Wiley & Sons, Ltd, Chichester,Chapter 11.

30. Schurtenberger, P. and Newman, M. E. (1993). Characterization of biological and environ-mental particles using static and dynamic light scattering. In Environmental Particles, edsBuffle, J. and van Leeuwen, H. P. IUPAC Series on Analytical and Physical Chemistry ofEnvironmental Systems, Vol. 2. Lewis, Boea Raton, FL.

31. Schmitt-Kopplin, P. and Junkers, J. (2006). Modern electrophoric techniques for the charac-terisation of natural Organic matter. In Environmental Colloids: Behaviour, Structure andCharacterisation, eds Wilkinson, K. J. and Lead, J. R. IUPAC Series on Analytical andPhysical Chemistry of Environmental Systems, Vol. 10. John Wiley & Sons, Ltd, Chichester,Chapter 6.

32. Buffle, J. (1998). Complexation Reactions in Aquatic Systems: an Analytical Approach. EllisHorwood, New York.

33. Droppo, I. G., Flannigan, D. T., Leppard, G. G., Jaskot, C. and Liss, S. N. (1996). Flocstabilization for multiple microscopic techniques, Appl. Environ. Microbiol. 62, 3508–3515.

34. Duval, J., Wilkinson, K. J., Buffle, J. and van Leeuwen, H. P. (2005). Humic substances aresoft and permeable: evidence from their electrophoretic mobilities, Environ. Sci. Technol. 39,6435–6445.

35. Villalobos, M., Bargar, J. and Sposito, G. (2005). Mechanisms of Pb(II) sorption on a biogenicmanganese Oxide, Environ. Sci. Technol., 39, 569–576.

36. Lead, J. R., Davison, W., Hamilton-Taylor, J. and Harper, M. (1999). Trace metal sorptionby natural particles and coarse colloids, Geochim. Cosmochim. Acta, 63, 1661–1670.

37. Moran, S. B. and Moore, R. M. (1989). The distribution of colloidal aluminium and organiccarbon in coastal and open ocean waters off Nova Scotia, Geochim. Cosmochim. Acta, 53,2519–2527.

38. Honeyman, B. D. and Santschi, P. H. (1992). The role of particles and colloids in the transportof radionuclides and trace metals in the oceans. In Environmental Particles, Vol. 1, (Buffle,J. and van Leeuwen, H. P., eds.), pp. 554, Lewis Publishers.

39. Wilkinson, K. J. and Buffle, J. (2004). Critical evaluation of physicochemical parametersand processes for modeling the biological uptake of trace metals in environmental (aquatic)systems. In Physicochemical Kinetics and Transport at Chemical–Biological Interphases, edsvan Leeuwen, H. P. and Koester, W. John Wiley & Sons, Ltd, Chichester, pp. 533.

40. Thang, N. M., Geckeis, H., Kim, J. I. and Beck, H. P. (2001). Application of the flow field-flow fractionation (fFFF) to the characterization of aquatic humic colloids: evaluation andoptimization of the method. Colloids Surf. A, 181, 289–301.

41. Redwood, P. S., Lead, J. R., Harrison, R. M. and Stoll, S. (2005). Characterization of humicsubstances by environmental scanning electron microscopy, Environ. Sci. Technol., in press.

42. Rizzi, F. R., Stoll, S., Senesi, N. and Buffle, J. (2004). A transmission electron microscopystudy of the fractal properties and aggregation processes of humic acids, Soil Sci., 169,765–775.

43. Balnois, E. and Wilkinson, K. J. (2002). Sample preparation techniques for the observationof environmental biopolymers by atomic force microscopy, Colloids Surf. A, 207, 229–242.

44. Radko, S. P. and Charambach, A. (2002). Separation and characterization of sub-mm- andmm-sized particles by capillary zone electrophoresis, Electrophoresis, 23, 1957–1972.

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