Trace-Element Contamination of the Environment PDF
Preview Trace-Element Contamination of the Environment
Fundamental Aspects of Pollution Control and Environmental Science 1 D. PURVES Trace-Element Contamination of the Environment 2 R.K. DART and R.J. STRETTON Microbiological Aspects of Pollution Control 3 D.E. JAMES, H.M.A. JANSEN and J.B. OPSCHOOR Economic Approaches to Environmental Problems 4 D.P. ORMROD Pollution in Horticulture 5 S.U. KHAN Pesticides in the Soil Environment 6 R.K. DART and R.J. STRETTON Microbial Aspects of Pollution Control (2nd edition) Overleaf: Atmospheric Pollution near Falkirk, Scotland. (Photograph: The Scotsman, Edinburgh). Fundamental Aspects of Pollution Control and Environmental Science 7 TRACE-ELEMENT CONTAMINATION OF THE ENVIRONMENT (REVISED EDITION) DAVID PURVES Central Analytical Laboratory/Trace Elements Department, Edinburgh School of Agriculture, Edinburgh (Scotland) ELSEVIER Amsterdam — Oxford — New York — Tokyo 1985 ELSEVIER SCIENCE PUBLISHERS B.V. Molenwerf 1 P.O. Box 211, 1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY, INC. 52 Vanderbilt Avenue New York, NY, 10017 Library of Congress Cataloging in Publication Data Purves, David. Trace-element contamination of the environment. (Fundamental aspects of pollution control and environmental science ; 7) Bibliography: p. Includes indexes. 1. Trace elements—Environmental aspects. I. Title. II. Series. TD196.TTPÖT 1985 363.7'3 65-10111+ ISBN 0-^-1*2503-9 ISBN: 0-444-42503-9 (Vol. 7) ISBN: 0-444-41611-0 (Series) © Elsevier Science Publishers B.V., 1985 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopy ing, recording or otherwise, without the prior written permission of the publisher, Else- vier Science Publishers B.V./Science & Technology Division, P.O. Box 330, 1000 AH Amsterdam, The Netherlands. Special regulations for readers in the USA — This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be ob tained from the CCC about conditions under which photocopies of parts of this publica tion may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the publisher. Printed in The Netherlands VII PREFACE Since the first edition of this book in 1977 there has been an explosion of interest in almost every aspect of research in environmental pollution. However, the purpose of this work remains the same. This is to evaluate the global biological consequences of dispersal of trace elements, originally mined from localized limited deposits in the environment. This is a kind of environmental pollution which has hitherto received less attention than the problem deserves, for it could have profound ecological consequences in the long term. In the soil this kind of contamination appears to be sometimes virtually irreversible and the health of plants and animals depends on the exclusion of potentially toxic trace elements from biological systems above low threshold limits of concentration. In this work, the problem of trace-ele.nent contamination of the biosphere is seen as one of a number of possible kinds of environmental pollution, and this problem is set in the context of the general ecological crisis with which all mankind is faced. The author wishes to thank Dr Gwendoline F. Berndt for reading the text and making constructive suggestions. Thanks are also due to Mrs Anna Lumsden for assistance in checking references. Acknowledgement is made to the Natural Environment Research Council, London, of a grant received for the purchase of specialized analytical equipment used in trace-element analysis of plant material. 1 INTRODUCTION It is now generally recognized, in enlightened scientific circles at least, that man faces an ecological crisis as a result of over-population and its attendant problems. The human species is unique among animals in that it strikes no stable population balance with the environment and makes little attempt to live in harmony with it. Associated with explosive growth in population we have an economic system which requires increasing consumption per capita per annum in order to operate satisfactorily. Within this system, as a necessary adjunct to it, we have developed highly sophisticated advertizing techniques to generate new demands leading to greater consumption and to convert human material wants to irreducible necessities. In a technologically advanced society which has developed the use of a wide range of metals, such an economic system puts great pressure on non-renewable resources, since it operates on the assumption that these are inexhaustible. A basic proposition inherent in the conventional wisdom associated with this system is that an increasing gross national product (GNP) is a measure of social progress. Since the GNP is a measure of the monetary value which can be attached to goods and services produced annually in any national community, and this includes the value attached to consumption of fossil fuels and minerals extracted from finite deposits, the GNP is also largely a measure of the rate at which non-renewable resources are depleted. The word 'progress' has therefore come to be synonymous with the movement of our society towards a state where it will be entirely dependent on renewable resources of energy and elements now obtained from mineral resources; this is to say towards impoverishment. The most pressing of the problems arising from our exploitative approach to the natural environment i* •»ndoubtedly the shortage of food in parts of the world dependent on large-scale importation of food supplies, but we also face a bewildering variety of problems arising from various kinds of environmental pollution and the prospect of exhaustion of non-renewable mineral and fossil fuel resources. The seriousness of the overall situation was underlined by the publication in 'The Ecologist' of Ά Blueprint for Survival' in 1972 [1] and by the formation of the Club of Rome. Although this monograph is not specifically concerned with the reasons behind our current predicament or with the philosophy inherent in the economic system which has produced it, it is important that the problems of environmental contamination it deals with are seen as part of the ecological crisis as a whole. 2 A distinction is sometimes made between contamination and pollution of the environment and Bowen [2] (p.213) has stated that contamination occurs when part of the environment changes its chemical composition as a result of human activity, without any obvious biological consequence. Since contamination is certainly a pejorative term, this definition is perhaps as indictment of human activity as compared with other kinds of biological activity. Contamination of the environment has to be regarded as the dispersion of some substance in it at concentrations which may produce undesirable effects - when the undesirable effects are evident, the contamination amounts to environmental pollution. The concept of contamination can therefore be said to include pollution, but since these are words associated with value judgements, neither can be given any precise definition in terms which can be quantified. With the exception of radio-activity, which is in quite a different category, all kinds of environmental contamination can be classified on the basis of the chemical nature of the contaminated material. On this basis, most problems fall into the following five categories: 1. Pollution from petroleum oil and oil wastes. 2. The creation of a localized biological oxygen demand resulting from the dispersal of organic wastes, such as sewage effluents, sewage sludge, faecal slurries from livestock, silage effluents, effluents from paper mills, municipal refuse and abattoir refuse. 3. Eutrophication of inland waters due to loss of nitrogen and phosphorus from the soil. 4. Contamination of the environment with specific toxic compounds such as inorganic acids and alkalis, and organic pesticides, fungicides and herbicides. 5. Dispersal of individual elements (usually metals), either singly or in association, in the environment. In practice, a problem of environmental contamination may involve contaminants in more than one category. For example, metals are to a large extent dispersed along with organic wastes which create a biological oxygen demand. Each of these kinds of environmental contamination may, of course, give rise to associated problems of amenity which require consideration independently of its ecological consequences. This work is specifically concerned with the last pollution category, and because our civilization is heavily dependent on the use of metals, gives particular attention to the situation created as a result of large-scale dispersion of metals in the land environment. Limits are set to this problem by the size of available global reserves of minerals, because the exhaustion of 3 these reserves will eventually prevent any further dispersion of the elements involved. According to the Blueprint for Survival , mankind is now rapidly using up these reserves and at present rates of consumption, all known reserves of silver, gold, lead, tin and zinc will be exhausted before the year 2000. It is predicted that the indispensable element, copper, will run out a few years later and that by the year 2150, the only metals in widespread use with known ore reserves will be iron and chromium. The situation appears even more serious if we assume an exponential increase in metal consumption, such as has occurred since 1960, for on this basis, all known metal reserves would be exhausted within 50 years, with the exception of iron and chromium. Although the latter scenario is the most pessimistic possible and takes no account of the possibility of the discovery of new ore reserves, the overall picture is alarming whatever figures we choose as a basis for calculating the length of time metal supplies will last. The urgent need to conserve non-renewable resources of metals therefore reinforces the need to prevent pollution problems arising from their dispersion in the environment. The two problems are complementary. The process of dispersal of elements naturally present at trace levels in the biosphere affects the whole system, although elements dispersed in the atmosphere do not remain there as permanent contaminants and are eventually deposited in the ocean or on land. The subject of atmospheric pollution and its consequences for health has received a great deal of attention since World War II [3, 4, 5] and in this work, the atmosphere is considered mainly as a possible route for the contamination of the hydrosphere and the exposed surface of the soil. Several elements used in industry find their way in large quantities into the ocean, but so great is the total volume of water involved that the ecological consequences of such additions are largely restricted to situations where dispersion has been delayed. The situation is radically different when the soil becomes contaminated, for in this case the dispersion is irregular and the environmental consequences may be locally persistent. The trace-element content of uncontaminated soil [6,7] largely reflects the composition of the rocks from which the soil parent material was derived and in most soils, the total content of any trace element is normally within defined limits dictated by geochemical considerations. Soil genesis is a process which has taken place on the geological time scale and during the millions of years of weathering of rocks which has been involved, the evolving soils have been subject to the action of rain. As a consequence, there is little water-soluble material present in most natural soils suitable for cultivation, and a relatively small fraction of the total content of each trace element is immediately available to plants, the bulk of each element being either chelated 4 in organic compounds, ionically bound on clay surfaces or trapped inside mineral crystal lattices. This is the environmental background against which all terrestrial animals have evolved. A completely novel situation is created when we apply to the soil a sewage sludge containing, say, 100 ppm of a potentially-toxic element like cadmium to a rural soil which naturally contains less than 1 ppm of this element. Man, like all other terrestrial animals, depends on food derived from the soil and the natural composition of the soil is, therefore, of vital importance to him. Having evolved against a background of a food supply based on virgin soil, the enzyme systems on which our metabolism is based, rely on the presence of essential trace elements in the diet (such as cobalt, copper, manganese and zinc) within certain limits of concentration and on the relative absence from the diet of toxic non-essential elements (such as antimony, arsenic, beryllium, cadmium, lead, mercury and thallium). This is to say that our internal biochemistry reflects the composition of the uncontaminated primeval biosphere, is attuned to this composition and is dependent on it. Mammals, unlike micro-organisms, plants and insects, are not in a position to adapt to any marked change in the normal trace element distribution pattern and we run the risk of creating serious biochemical difficulties for ourselves if we allow the soil to be contaminated in the long term with potentially toxic trace elements which can pass into plants and thence into food chains. To some extent, this process is already under way and some unessential potentially-toxic trace elements now appear to be present in human protoplasm in unnaturally high concentrations. Hecker et dl. [8], in a comparison of 100 acculturated and 90 unacculturated individuals, found that the levels of lead and cadmium were markedly lower in the hair, blood and urine in the unacculturated population. Since the latter was composed of Yanomamo Indians living in remote areas of Venezuela, the levels associated with this population' can probably be taken to reflect an environment virtually uncontaminated by trace elements derived from industrial sources. In the long term, this kind of environmental pollution may turn out to be more serious than any other kind, with the possible exception of radio-active contamination, for organic matter, however noxious or stable, is eventually degraded by microbial action; elements remain, and their dispersion in the environment effects a permanent alteration in the composition of the biosphere. It is also obvious that the dispersion of elements, some of which are metals on which our civilization depends, is largely an irreversible process and that our descendants will have no means of recovering these elements, once this process approaches completion. Theoretically, it is, of course, possible to extract metals at a low concentration from any source material and the present trend is to extract
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