A Thesis Entitled the OCCURRENCE and BEHAVIOUR of CADMIUM IN
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a thesis entitled THE OCCURRENCE AND BEHAVIOUR OF CADMIUM IN SOILS AND ITS UPTAKE BY PASTURE GRASSES IN INDUSTRIALLY CONTAMINATED AND NATURALLY METAL RICH ENVIRONMENTS submitted for the degree of Doctor of Philosophy in the Faculty of Science of the University of London by ALAN EDWIN MARPLES Royal School of Mines March 1979 Imperial College London -2- ABSTRACT Cadmium has been recognised as an environmental pollutant and the presence of high concentrations in agricultural soils can lead to accumulation of the metal in man. Detailed surveys are described which ascertain the extent and intensity of enrichment/contamination in soils associated with i) metal-rich black shales in Derbyshire and Staffordshire; ii) past lead and zinc mining and smelting in Derbyshire; iii) 19th century zinc mining in Somerset, and iv) modern zinc and lead smelting at Avonmouth. Cadmium is shown to be highly dispersed in all environments, with maximum concentrations of about 40 pg/g in surface soils. Soils developed on abandoned zinc workings in Somerset contain up to 800 pgCd/g. In parts of the Upper Tawe Valley, South Wales, cadmium is shown to have accumulated in stream sediments, although soils are relatively unaffected. The source of the metal is likely to be atmospheric particulate matter from recent zinc smelting in the Lower Swansea Valley. Black shale, ore minerals and atmospheric particulate are the major sources of cadmium and examinations have been carried out on typical samples from each area studied. The movement of these materials into soils and the subsequent dispersion of cadmium has been investigated by examination of the distribution of the metal in soil profiles. Selective chemical extractants have been employed to determine the form of cadmium in soils. A high proportion (up to 510) of the total metal is present in an 'available' form and leaching into soil-, ground-, and surface- waters has been demonstrated. -3- The transmission of cadmium from soils to man along the food chain depends on the efficiency with which plants accumulate the metal. Uptake of cadmium by pasture grasses has been shown to be limited under natural conditions in all areas. Very low concen- trations are found in the aerial parts of plants grown on highly contaminated soil. Uptake is enhanced under greenhouse conditions, especially from soils treated with inorganic nitrogenous fertilisers. It can also be reduced by the use of cow slurry as a nutrient source. -4- A CIiNOVILEDGE ENT The work described in this thesis was carried out at the Applied. Geochemistry Research Group, Imperial College, under the direction of Professor J.S. Webb, between 1975 and 1977. The programme was funded by RTZ Services Ltd., Bristol and ' I acknowledge the receipt of financial support from the Company in the form of an RTZ Research Bursary. I wish to thank Dr. lain Thornton, who supervised the project, for his advice, his helpful comments on writing the thesis and for carefully editing the text. I wish to thank Dr. A.K. Barbour, RTZ Services Ltd., for his interest in the work. I acknowledge the help of the management of Commonwealth Smelting Limited, Avonmouth who made available partial data on atmospheric emissions from the smelter. In particular I wish to thank Mr. Bob Wakeley who provided soil samples collected in 1962, 1965 and 1968 and supervised the sampling of groundwaters at Avonmouth. I am very grateful for his helpful advice on environmental problems at Avonmouth, for his generous hospitality and for giving me a detailed and informative tour of the works. I wish to acknowledge the use of analytical facilities in the Applied Geochemistry Research Group. I am grateful to the technical staff for their assistance, particularly Mr. A. J. Thompson who gave advice on the determination of low levels of cadmium and suggested the dithizone solvent extraction method. I wish to thank contemporary post graduate students Steve Earle and Brian Reynolds for helpful discussions, Dick Campain who made available rock samples from Shipham and post graduate students in i;ining Geology for their advice on the optical -5- identification of ore minerals. My thanks also to Dennis Bailey who made the pclished thin sections and Neil Wilkinson who operated the electron probe. Pot experiments were carried out in greenhouses belonging to the Botany Department at Imperial College Field Station, Silwood Park, and I am grateful to Dr. B.J. Wheeler for the use of these facilities. I wish to thank 1r. Ted Green and his staff for help in running these experiments. Scanning electron microscopy was carried out in the Physiology Department at the National Institute for Research in Dairying, Reading, and I wish to thank Mr. B.E. Brooker for use of these facilities and Mr. D. Hobbs for technical assistance. I also thank the many farmers upon whose land the work was carried out for their help and hospitality. I acknowledge the help of the Ministry of Agriculture, Fisheries and Food, A.D.A.S., Cardiff who carried out the organic matter determinations on soils from the Upper Tage Valley. I wish to acknowledge the help of the library staff at the Zinc/Lead Development Association in searching the literature and for the use of their microfilm reading facilities. Finally, my thanks to Ms. Carol Simpson who typed the thesis and to the staff at B.N.F.L., Windscale who helped with its completion. A.E.I. -6- LIST OF CONTENTS PART ONE INTRODUCTION AND REVIEW 18 CHAPTER 1 THE GEOCHEMISTRY OF CADMIUM 19 1.1 Introduction 19 1.2 Mineralogy 19 Cadmium in Rocks 20 la Cadmium in Soils 21 1.4.1 Cadmium in unpolluted soils 21 1.4.2 Cadmium in polluted soils (industry) 23 1.4.3 Cadmium in polluted soils (agriculture) 24. 1. Cadmium in Waters 25 1.6 The Distribution of Cadmium in England and Wales 26 1 2 The Chemistry of Cadmium in the Natural Environment ~7 1.7.1 The element 27 1.7.2 Insoluble salts 28 1.7.3 Hydrolysis and inorganic complexation 28 1.7.4 Solubility equilibria in natural systems 29 1.7.5 Organic complexes 30 1.7.6 Cadmium interactions with inorganic soil colloids 31 1.7.7 Cadmium adsorption by soils 32 CHnPTER 2 CADMIUM IN INDUSTRY 40 2.1 Introduction 40 2.2 The British Zinc Industry 40 2.2.1 Mining and ore processing 40 2.2.2 Pyrometallurgical recovery of zinc metal 42 2.2.3 The history of the British industry 44 2.3 The Recovery of Cadmium 45 2_4 The Production and Uses of Cadmium 46 2.5 Environmental Control and Industrial Hygiene 47 2.5.1 Mining and ore beneficiation 47 2.5.2 Smelting and refining 48 2.5.3 Fabrication of cadmium products 19 2.6 Cadmium in Air 50 2.6.1 Atmospheric concentrations and rates of deposition 50 2.6.2 The retention of airborne particles by vegetation 51 -7- 2.6.3 Monitering heavy metals in air 52 2.6.4 Characteristics of heavy metal particles 53 CHAPTER 3 CADMIUM IN PL NTS,: ANIMALS AND MAN 57 3.1 Introduction 57 Cadmium in Plants 58 3.2.1 Cadmium concentrations in plant tissues 58 3.2.2 Uptake studies using culture solution 58 3.2.3 Uptake studies using CdC12 amended soil 59 3.2.4 Uptake studies using sludge amended soil 60 3.2.5 Cadmium uptake from other sources 61 3.2.6 Cadmium in rice 62 3.2.7 Cadmium pollution of grassland 62 3.2.8 Revegetation of mine spoil and the evolution of metal tolerance 63 ILI Toxicology of Cadmium in Han 63 3.3.1 Forms of toxicity 63 3.3.2 Epidemiology of cadmium poisoning 64 .1 Toxicology of Cadmium to Grazing Livestock 65 PART TWO THE DISTRIBUTION OF CADMIUM IN SOILS 69 CHAPTER 4 THE DISTRIBUTION OF CADMIUM IN SOILS IN RELATION TO NATURAL AND INDUSTRIAL SOURCES 70 4.1 Introduction 70 4.2 Method oloa 70 The Geology and Soils of the Southern Pennines 71 4.4_..._ Onecote and Bradbourne - a Black Shale Source of Cadmium 74 4.4.1 Description of the area 74 4.4.2 Results 75 4.4.3 Discussion 76 and 4.5 Youl•reave Tideslow Wormhill Stoned_e a Lead Mining Source of Cadmium 77 4.5.1 Description of the area 77 4.5.2 Results 79 4.5.3 Discussion 80 Geology and Soils of the Bristol District 82 -8- Shipham - a Zinc Mining Source of Cadmium 84. 4.7.1 Description of the area 84 4.7.2 Results 85 4.7.3 Discussion 86 Avonmouth and Severnside - a Zinc Smelter Source of Cadmium 87 4.8.1 Description of the area 87 4.8.2 Results 88 4.8.3 Discussion 90 4.8.4 Cadmium contamination at Avonmouth between 1962 and 1976 91 4. Conclusions 92 CHAPTER 5 THE UPPER TAME VALLEY 118 .1 Introduction 118 .2 Description of the Area 118 .' Results 120 .2.1A Trace Elements in Rainfall 122 . Discussion 123 PART THREE THE SOIL CHEMISTRY OF CADMIUM 133 CHAPTER 6 IDENTIFICATION OF THE CADMIUM SOURCE 'ATERIALS 134 6.1 Introduction 134 6.2 Cadmium in Black Shales 134 62.2 Cadmium in Zinc and Lead Orebodies 136 66.1. Cadmium in Modern Smelter Emissions 140 Conclusions 142 CHAPTER THE DISTRIBUTION OF CADMIUM IN SOIL PROFILES 153 211 Introduction 153 12 Profile Description and Horizon Notation 154 Soil Profiles in the Onecote - Bradbourne Study Area 155 7.3.1 Interfluve and mid-slope soils 155 -9- 7.3.2 Base of slope and alluvial soils 156 7.3.3 Discussion 157 Soil Profiles in the Youlgreave-Tideslow-Stonedge Study Area 158 7.4.1 Disturbed profiles on abandoned lead workings 158 7.4.2 Undisturbed profiles adjacent to lead workings 159 7.4.3 Profiles at an abandoned lead smelter 160 7.4.4 Discussion 161 212 Soil Profiles in the Shitham Study Area 162 7.5.1 Disturbed profiles on abandoned zinc calamine workings 162 7.5.2 Undisturbed profiles adjacent to abandoned calamine workings 163 7.5.3 Discussion 163 Z Soil Profiles in the Avonmouth-Severnside Study Area 161+ 7.6.1 Profiles on the alluvial plain