Durham E-Theses Arsenic in the environment Jones, Iwan E. LI. How to cite: Jones, Iwan E. LI. (1997) Arsenic in the environment, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/4730/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk ARSENIC IN THE ENVIRONMENT by Iwan E. LI. Jones A dissertation submitted to the University of Durham in fulfilment of the requirement for the degree of MSc by Research The copyright of this thesis rests with the author. No quotation from it should be published without the written consent of the author and information derived from it should be acknowledged. September 1997 5 MAR m ACKNOWLEDGEMENTS In the writing of this work, I must first thank Dr Stephen Thomas for the initial opportunity to study for a PhD. Since then, he has been a continued help in the search for funding in various shapes and forms, and although this work is not in his field of expertise, he has maintained a continued interest in its progress, and occasionally provided me with an opportunity to work back in the 'real world'. I must also thank my 'secondary' supervisor, Dr John Wilson for help with the many things bureaucratic that universities seem to love so much, his patience and humour with such things causes nothing much short of complete admiration. Thanks must also go to a number of researchers outside Durham University, who kindly provided me with reports and reprints of their research papers. These include Prof. Bill Davison and Dr Hao Zhang of Lancaster University; Dr Andrew Hursthouse of the University of Paisley and Michael Riley of S. S. Papadopulos & Associates, Inc. of Boulder, Colorado. I must sincerely thank my parents for their continued support over the course of the past three years, the good humour of my sisters, Angharad and Catrin and their families, and also the patience exhibited by my somewhat long suffering girlfriend, Rachel. My friends at Durham Amateur Rowing Club have provided me with an excuse not to go completely mad, although perhaps they might not be so sure. My thanks also go to a number of friends who have helped me with comments of pure cynicism when I was in a mood to throttle someone! Such dubious characters are too numerous to name individually, but include Andrew Adams, Tony Leopold, Fran Brearton, Lynne Beaton, Emily Williams, John McGroary, Ros Martin, Paula Russell, Richard Mortimer, GwiUym and Pamela Roberts, y teulu Bodlew, Adonis Giolas, Doug Langton, Jeremy Lloyd, Pete and Aila Bursnall, Dave-the-Leg, Aids Stevens; Dave Barham, Mark Briggs, and of course Rod and Anna White. ABSTRACT Arsenic, long synonymous in people's mind with poison exhibits a varied, fascinating and dynamic biogeochemistry. Chemically and biologically reactive, its chemical form, or speciation, changes with slight variations in chemical or biological conditions. Depending upon the extent to which any arsenic containing system is dominated by physical/chemical or biological process, the forms of arsenic may change between the various inorganic and methylated species, and may alter rapidly with varying conditions. Early research revolved around the formulation of pigments, and later in the development of effective medicines. Later stiU, thanks due to its long history as a poison, arsenic was included in numerous agricultural practices, mainly as a herbicide or pesticide. It has also seen service in the rather more specialised field of chemical warfare, and still poses threats as a result of improper disposal. Much of the recent research has focused on the identification of previously unknown organoarsenic species foimd in estuarine and marine waters. This work is building up an understanding of the biological pathways involved in the biochemical cycling of arsenic. Littie work has been carried out with respect to the cycling of arsenic in freshwaters in comparison to that in marine and estuarine waters. Similarly, there has been less work performed on the speciation of arsenic in freshwater sediment interstitial waters, than there has on marine sediments, or intertidal sediments. The characterisation of arsenic in dynamic porewater poses a set of unusual and difficult problems, not the least being the procurement of representative, discrete samples. A number of potential sampling methods are reviewed, and variations on the thin film gel sampling technique are thought to provide perhaps the best option, although this will depend upon the type of intertidal sediment being investigated, and the information sought. It may be impossible to propose a general model of arsenic cycling either at a local scale or at a global level. This is of course due to the great diversity in ecosystems, each having different controls over arsenic speciation, and containing different biological commimities. Once a given system has been described, the patterns of arsenic speciation (both spatially and temporally) are explainable, and potential impacts can be identified, but they carmot be transferred to another system. The continuing accumulation of information regarding arsenic speciation in different systems is helping in the unravelling of the larger global arsenic cycle. Such an understanding can only be a benefit in the development of safe and efficient remediation schemes for contaminated soil and aquatic systems. m CONTENTS Section Page Number Title 1 Acknowledgements ii Abstract iii Contents iv List of tables X List of figures xiii Chapter 1 Introduction Chapter 2 Occurrence of Arsenic 2.1 Introduction 6 2.2 Rocks 7 2.2.1 Rock arsenic speciation 10 2.3 Soils 10 2.3.1 Soil arsenic speciation 12 2.4 Natural waters 14 14 2.4.1 Groundwater and geothermal waters 16 2.4.2 Seawater 16 2.4.2.1 Photic zone 19 2.4.2.2 Deeper waters 20 2.4.3 Estuarine waters and sediments 22 2.4.4 River and lake waters and sediments 2.5 Air masses and precipitation 24 2.5.1 Atmospheric arsenic speciation 26 2.6 Living things 28 2.6.1 Accumulation 30 2.6.2 Marine organisms 31 2.6.3 Freshwater organisms 32 2.6.4 Marine plants 33 2.6.5 Freshwater plants 34 2.6.6 Terrestrial organisms 35 2.6.7 Terrestrial plants 38 2.7 Anthropogenic inputs 41 2.7.1 Mining, smelting and power generation 41 2.7.2 Soil additions 43 2.7.3 Pollution and disposal 45 2.7.3.1 Out-of-sight-out-of-mind 45 2.7.3.2 Political reasoning 46 2.7.3.3 Industrial incidents 48 2.7.3.4 Non-point source 48 IV Chapter 3 Uses, Production and Global Mass Balance 3.1 Introduction 50 3.2 Uses of Arsenic 50 3.2.1 Alloys 50 3.2.2 Medicines 50 3.2.3 Pigments and poisonings 51 3.2.4 Glass manufacture 54 3.2.5 Agriculture 54 3.2.6 Wood preservatives 56 3.2.7 Electronics 56 3.2.8 Warfare 57 3.2.9 Embalming 57 3.2.10 Mineral prospecting 58 3.3 Arsenic production 58 3.3.1 Arsenic substitutes 61 3.3.2 Resources 62 3.4 Global arsenic mass balance 62 Chapter 4 Redox Reactions and Solubility 4.1 Introduction 70 4.2 pH 71 4.3 Eh 72 4.4 Eh and pH in natural systems 75 4.4.1 pH-Eh or pH-pE diagrams 76 4.4.2 Drawbacks with pH-Eh or pH-pE diagrams 78 4.5 Interactions with solids (oxidation/reduction processes) 79 4.6 Arsenic as a redox indicator 81 4.7 Arsenic redox rates 82 4.8 Removal from solution/solid phase and transport 84 4.8.1 Inorganic arsenic adsorption 85 4.8.2 Organoarsenic adsorption 88 4.8.3 Adsorption isotherms 89 4.8.4 Sorption (coprecipitation and adsorption) 91 4.8.4.1 Iron 93 4.8.4.2 Manganese 95 4.8.4.3 Aluminium and clay 96 4.8.4.4 Sulphide 97 4.8.4.5 Organic matter 99 4.9 Arsenic solubility 100 4.10 Arsenic mobility in the environment 101 4.10.1 Atmospheric arsenic redox reactions 102 4.10.2 Sand columns, muds and sediments 103 4.10.3 Mine spoil 106 4.10.4 Stratified lakes 108 4.10.4.1 Seasonality 110 4.10.4.2 Porewaters 111 4.10.5 Sediment-water interface 111 Chapter 5 Biochemistry and Ecotoxicology 5.1 Introduction 115 5.2 Methylation 120 5.3 Formation of methylarsenicals 122 5.3.1 Methyl transfer from SAM 123 5.3.2 Vitamin B^ dependent methyl transfer 125 5.4 ExoceUular or abiotic methylation 128 5.5 Demethylation 129 5.6 Biologically mediated redox rates 130 5.7 Seasonality 132 5.8 Complex organoarsenicals 133 5.9 Ecotoxicology 134 5.9.1 Essentiality 136 5.9.2 Arsenic toxicity 137 5.9.3 Routes of exposure 139 5.9.4 Rate of excretion 141 5.9.5 Method of action 142 5.9.6 Effects of arsenic intoxication 144 5.9.7 Phytotoxicity 147 5.9.8 Carginogenicity? 148 5.9.9 Arsenic health risk assessment 150 Chapter 6 Sample Collection 6.1 Introduction 154 6.2 Porewater sampling methods 155 6.2.1 Centrifugation 156 6.2.2 Squeezing 157 6.2.3 Vacuum filtration 160 6.2.4 Dialysis 161 6.2.5 Thin film gels 164 6.2.5.1 Diffusive equihbrium 164 6.2.5.2 Diffusive gradient 166 6.2.6 Proposed porewater sampling device 168 6.2.6.1 Sampler materials 178 6.3 SoU and water sampling 179 6.3.1 Soil sampling 179 6.3.2 Surface water sampling 179 6.3.3 Groundwater sampling 180 Chapter 7 Sample Preservation