Metal Contamination of Food Its Significance for Food Quality and Human Health Third edition Conor Reilly BSc, BPhil, PhD, FAIFST Emeritus Professor of Public Health Queensland University of Technology, Brisbane, Australia Visiting Professor of Nutrition Oxford Brookes University, Oxford, UK Metal Contamination of Food Metal Contamination of Food Its Significance for Food Quality and Human Health Third edition Conor Reilly BSc, BPhil, PhD, FAIFST Emeritus Professor of Public Health Queensland University of Technology, Brisbane, Australia Visiting Professor of Nutrition Oxford Brookes University, Oxford, UK # 2002 by Blackwell Science Ltd, First edition published 1980 by Elsevier Science a Blackwell Publishing Company Publishers Editorial Offices: Second edition published 1991 Osney Mead, Oxford OX2 0EL, UK Third edition published 2002 by Blackwell Tel: +44 (0)1865 206206 Science Ltd Blackwell Science, Inc., 350 Main Street, Malden, MA 02148-5018, USA Library of Congress Tel: +1 781 388 8250 Cataloging-in-Publication Data Iowa Street Press, a Blackwell Publishing Company, Reilly, Conor. 2121 State Avenue, Ames, Iowa 50014-8300, USA Metal contamination of food:its significance Tel: +1 515 292 0140 for food quality and human health/Conor Blackwell Publishing Asia Pty Ltd, 550 Swanston Reilly. ± 3rd ed. Street, Carlton South, Melbourne, Victoria 3053, p. cm. Australia Includes bibliographical references and index. Tel: +61 (0)3 9347 0300 ISBN 0-632-05927-3 (alk. paper) Blackwell Wissenschafts Verlag, 1. Food contamination. 2. Food ± Anlaysis. KurfuÈ rstendamm 57, 10707 Berlin, Germany 3. Metals ± Analysis. I. Title. Tel: +49 (0)30 32 79 060 TX571.M48 R45 2003 363.19'2 ± dc21 The right of the Author to be identified as the 2002026281 Author of this Work has been asserted in accordance with the Copyright, Designs and ISBN 0-632-05927-3 Patents Act 1988. A catalogue record for this title is available from the All rights reserved. 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For further information on Blackwell Science, visit our website: www.blackwell-science.com Contents Preface to the third edition xiii Preface to the second edition xv Preface to the first edition xvii Part I:The Metals We Consume 1 1 Introduction 3 1.1 Ash 3 1.1.1 Ash and the early food analysts 3 1.1.2 A nineteenth-century view on food ash 4 1.1.3 Ash in the modern food laboratory 5 1.2 The metals in food 5 1.2.1 Chemical properties of the metals 7 1.2.2 Representative and transition metals 7 1.3 Distribution of the metals in the environment 8 1.3.1 Metals in human tissue 8 1.3.2 Metals in soil 8 1.3.2.1 Soil as a source of plant trace elements 8 1.3.2.2 Variations in the metal content of soils 9 1.3.2.3 Soil metal availability 9 1.3.2.4 Metal transport and location within the plant 10 1.3.2.5 Soil metal speciation 10 2 Metals in food 12 2.1 The metal components of food 12 2.2 Why are we interested in metals in food? 13 2.2.1 Functions of the trace elements 13 2.2.2 New trace elements 14 2.3 The toxic metals 15 2.4 Effects of metals on food quality 16 2.5 How much metal do we consume with our food? 16 2.5.1 Estimating metal intakes 17 2.5.1.1 Surveillance methods for assessing intake 18 2.5.1.2 Duplicate diet method for intake estimation 18 2.5.2 Comparison of methods of assessment of metal intakes 19 2.6 Assessing risks from metals in food 19 3 Metal analysis of food 23 3.1 The determination of metals in foods and beverages 23 3.1.1 The first step in analysis:obtaining a representative sample 23 v vi Contents 3.1.2 Prevention of contamination 24 3.1.3 Drying of samples 24 3.1.4 Purity of chemical reagents and water 25 3.1.5 Glassware and other equipment 25 3.2 Preparation of samples for analysis:digestion of organic matter 25 3.2.1 Dry ashing 25 3.2.2 Wet digestion techniques 26 3.2.2.1 Nitric acid digestion 26 3.2.2.2 Nitric±sulphuric acids digestion 27 3.2.2.3 Use of perchloric acid 27 3.2.2.4 Hydrofluoric acid 27 3.2.3 Microwave digestion 27 3.3 End-determination methods for metal analysis 28 3.3.1 Atomic absorption spectrophotometry (AAS) 29 3.3.1.1 Background correction 29 3.3.1.2 Use of slurries and flow injection in AAS 29 3.3.1.3 Speeding up AAS 30 3.3.2 Spectrofluorimetry 30 3.3.3 Inductively coupled plasma spectrometry (ICP-S) 31 3.3.3.1 Inductively coupled plasma atomic emission spectrometry (ICP-AES) 31 3.3.3.2 Inductively coupled plasma mass spectrometry (ICP-MS) 31 3.3.4 Other analytical techniques for trace elements 32 3.4 Determination of elemental species 32 3.4.1 Methodology for the determination of metal species 33 3.4.1.1 Chemical methods of speciation 33 3.4.1.2 Hyphenated techniques for metal speciation 33 3.5 Analytical quality control 34 4 How metals get into food 40 4.1 Metals in the soil 40 4.1.1 Uptake of metals by plants 41 4.1.1.1 Accumulator plants 41 4.1.1.2 Geobotanical indicators 41 4.1.2 Effects of agricultural practices on soil metal content 42 4.1.2.1 Metals in agricultural fertilisers 42 4.1.2.2 Metals in sewage sludge 43 4.1.2.3 Metal uptake from agrochemicals 45 4.1.3 Industrial contamination as a source of metals in food 45 4.1.3.1 Metal contamination from mining operations 46 4.1.3.2 Metal contamination from metal industries 46 4.1.3.3 Emission of metals from coal 48 4.1.3.4 Problems of use of brownfield sites 48 4.1.4 Geophagia 49 4.2 Metal contamination of food during processing 49 4.2.1 Contamination of food from plant and equipment 50 4.2.2 Metal pick-up during canning 50 4.2.2.1 `Tin' cans 51 4.2.2.2 Aluminium containers 52 4.2.3 Contamination of food during catering operations 53 4.2.3.1 Metal cooking utensils 53 Contents vii 4.2.3.2 Ceramic ware 55 4.2.3.3 Enamelled ware 56 4.2.3.4 Other domestic sources of metal contamination of food 56 4.3 Food fortification 57 4.3.1 Regulations and current practice regarding fortification of foods 57 4.3.1.1 UK regulations 58 4.3.1.2 Australian and New Zealand regulations 58 4.3.2 Foods commonly fortified 59 4.3.2.1 RTE breakfast cereals 59 4.3.2.2 Functional foods 59 4.3.3 Natural fortification of foods with metals 60 5 Metals in food and the law 67 5.1 Why do we have food legislation? 67 5.1.1 International and national legislation 69 5.1.1.1 UK legislation on metals in food 69 5.1.1.2 US legislation on metals in food 71 5.1.1.3 Legislation in Australia and elsewhere in the English-speaking world 72 5.1.1.4 International standardisation and harmonisation of food laws 74 5.1.1.5 European Community food regulations 75 5.2 Codes of practice 76 Part II:The Individual Metals 79 6 The persistent contaminants:lead, mercury, cadmium 81 6.1 Lead 81 6.1.1 Chemical and physical properties of lead 82 6.1.2 Production and uses 82 6.1.3 Lead in the human body 84 6.1.4 Biological effects of lead 85 6.1.5 Lead in food and beverages 87 6.1.5.1 Lead in meat and offal 87 6.1.5.2 Lead in canned foods 87 6.1.5.3 Lead in wines 88 6.1.5.4 Lead in home-grown vegetables 88 6.1.5.5 Lead in water 89 6.1.6 Adventitious sources of dietary lead 89 6.1.6.1 Lead in alcoholic beverages 89 6.1.6.2 Lead in dietary supplements 90 6.1.6.3 Lead in plastic packing 90 6.1.7 Dietary intake of lead 91 6.1.7.1 Lead in children's diets 91 6.1.8 Analysis of foodstuffs for lead 93 6.2 Mercury 94 6.2.1 Chemical and physical properties of mercury 94 6.2.2 Environmental distribution of mercury 95 6.2.3 Production and uses of mercury 96 6.2.4 Biological effects of mercury 96 6.2.5 Mercury in food 97 6.2.6 Analysis of foodstuffs for mercury 99 viii Contents 6.3 Cadmium 100 6.3.1 Chemical and physical properties of cadmium 101 6.3.2 Production and uses of cadmium 101 6.3.3 Cadmium in food 102 6.3.4 Cadmium in water and other beverages 104 6.3.5 Dietary intake of cadmium 104 6.3.6 Uptake and accumulation of cadmium by the body 104 6.3.7 Effects of cadmium on health 105 6.3.8 Analysis of foodstuffs for cadmium 106 7 The packaging metals:aluminium and tin 115 7.1 Aluminium 115 7.1.1 Chemical and physical properties of aluminium 116 7.1.2 Production and uses 116 7.1.3 Aluminium in food and beverages 117 7.1.3.1 Aluminium in fresh foods 117 7.1.3.2 Aluminium in processed foods 118 7.1.3.3 Aluminium in infant formulas 119 7.1.3.4 Aluminium in beverages 120 7.1.3.5 Aluminium in domestic water 120 7.1.3.6 Levels of aluminium in bottled waters and canned soft drinks 121 7.1.3.7 Aluminium in brewed tea 121 7.1.3.8 Aluminium in alcoholic beverages 121 7.1.4 Dietary intake of aluminium 121 7.1.4.1 High consumers of aluminium 122 7.1.4.2 Adventitious contributions of aluminium to the diet 122 7.1.5 Aluminium absorption 123 7.1.5.1 Metabolic consequences of high aluminium absorption 124 7.1.6 Analysis of foodstuffs for aluminium 124 7.2 Tin 125 7.2.1 Chemical and physical properties of tin 126 7.2.2 Production and uses of tin 126 7.2.3 Tin in food and beverages 127 7.2.3.1 Organotin compounds in food 128 7.2.4 Dietary intakes of tin 129 7.2.5 Absorption and metabolism of tin 129 7.2.6 Analysis of foodstuffs for tin 130 8 Transition metals:chromium, manganese, iron, cobalt, nickel, copper and molybdenum 137 8.1 Chromium 138 8.1.1 Chemical and physical properties of chromium 138 8.1.2 Production and uses of chromium 139 8.1.3 Chromium in food