\f\w the relationship between environmental lead and blood lead in children a study in environmental epidemiology bert brunekreef THE RELATIONSHIP BETWEEN ENVIRONMENTAL LEAD AND BLOOD LEAD IN CHILDREN - A STUDY IN ENVIRONMENTAL EPIDEMIOLOGY Department of Environmental and Tropical Health Agricultural University of Wageningen The Netherlands Report 1985 - 211 ;ENTRALE LANDBOUWCATALOGUS OOOO 0086 4740 Promotoren dr. K. Biersteker, hoogleraar gezondheidsleer, meer in het bijzonder de milieuhygiëne en de tropische gezondheidsleer dr. R.L. Zielhuis hoogleraar sociale geneeskunde, in het bijzonder ten aanzien van arbeid, sport en milieu *, aan de Universiteit van Amsterdam Co-promotor dr. J.P. Vandenbroucke, Instituut Epidemiologie, Erasmus Universiteit Rotterdam BIBLIOTHEEK DEK LANDBOUWH OGESCBOO& WAGKNINGEN Bert Brunekreef The relationship between environmental lead and blood lead in children: a study in environmental epidemiology. Proefschrift ter verkrijging van de graad van doctor in de landbouwwetenschappen, op gezag van de rector magnificus, dr. CC. Oosterlee, in het openbaar te verdedigen op vrijdag 17 mei 1985 des namiddags te vier uur in de aula van de Landbouwhogeschool te Wageningen TABLE OF CONTENTS 0. Introduction 1 0.1. Aim and structure of report 1 0.2. Motivation for a review of studies 2 on the relationship between environmental lead and blood lead in children 0.3. Background of environmental impact study 2 in Rotterdam, The Hague and Zoetermeer 1. Environmental health aspects of lead 4 1.1. Lead in the environment and in man 4 1.2. Children as a population at risk for lead 8 1.3. The exposure system 12 2. Methodological issues in studies on 16 relationships between environmental lead and blood lead in children 2.1. Preface 16 2.2. Environmental pathways of 17 lead to children 2.3. Exposure-dose relationships 22 2.4. The concentration of lead in blood 25 as dependent variable 2.5. Factors other than lead intake which 29 affect the concentration of lead in blood 2.6. Identification of confounding factors 32 2.7. Mathematical issues 41 3. Literature review of studies on relationships 46 between environmental lead and blood lead in children 3.1. Introductory remarks 46 3.2. Studies performed near industrial lead 47 sources 3.3. Studies performed in urban areas where 64 lead pollution is mainly caused by vehicular traffic 3.4. Other studies 74 3.5. Summary of pathway impact estimates 78 3.6. The scientific basis of standards for 82 environmental lead 3.7. Urban/suburban differences in blood 84 lead, associations between gasoline lead and blood lead, and the Turin Isotopic Lead Experiment 4. The relationship between environmental lead 85 and blood lead in Dutch city children 4.1. Preface 85 4.2. General design of the study 85 4.3. Choice of population 87 4.4. Assessment of exposure - methods 89 4.5. Assessment of exposure - results 94 4.6. Assessment of the concentration of 104 lead in blood 4.7. Factors affecting lead levels in the 107 envi ronment 4.8. Factors affecting ingestion and 108 internal exposure 4.9. Confounding factors 109 4.10. The relationship between environmental 110 lead and blood lead 4.11. The origins of lead in the environment 118 4.12. General discussion 122 5. Concluding Remarks 129 Summary 130 Samenvatting 133 References 136 Appendices: 1. Variability of exposure measurements and what it 159 does to regression analyses in epidemiology 2. Excerpt from questionnaire and questionnaire 161 resul ts 3. Regression equations and plots of Ln PbB vs 165 exposure variables and confounders 4. Correlation matrices of variables concerning 179 the origin of lead in the environment Bibliography 181 Acknowledgements 183 Curriculum Vitae 185 "De wagen ging de heirweg, een stroom van lood door het land. De chauffeur liet hem uitlopen, met geweldig ontploffen." F. Bordewijk "Knorrende beesten", 1933 0. INTRODUCTION 0.1. Aim and structure of report Although the concentrations of lead in the air and in man have declined in most industrialized countries in recent years, the hazards of environmental lead pollution continue to raise inte• rest and concern. Several recent studies have documented or suggested that adverse health effects of lead occur at blood lead levels which were considered safe only a few years ago. Other studies have empha• sized the importance of ingestion of soil and dust particles as a mode of lead intake for young children, who form a population at risk for lead for other reasons too. The above-mentioned developments call for a re-evaluation of environmental quality standards for lead. The key elements of such standards are the blood lead threshold and the impact of environmental lead exposure on blood lead concentrations of chil• dren. It may be necessary to adopt a lower blood lead threshold whereas at the same time, the impact of environmental lead expo• sure on children's blood lead is probably greater than was as• sumed previously. In The Netherlands, the national Health Council has already proposed a guideline for the long term average concentration of lead in air of 0.5 ug/m3 (Health Council 1984). This guideline is 3-4 times lower than comparable guidelines used in the United States, the Federal Republic of Germany and the United Kingdom. In the U.S., the Ambient Air Quality Standard for lead is currently under revision (EPA 1983, 1984). In this report, the impact of environmental lead exposure on children's blood lead is subjected to a detailed study. Chapter 1 provides a summary of the environmental health aspects of lead. In chapter 2, methodological issues in studies on correlations between environmental lead and blood lead in children are discus• sed. The report further proceeds along two lines: it contains a critical review, of studies from which quantitative estimates of the impact of environmental lead exposure on children's blood lead can be obtained {chapter 3), and it gives an account of a study on the association between blood lead and lead in the environment which was performed among a population of Dutch 1 children living in Rotterdam, The Hague and Zoetermeer in 1981 (chapter 4). 0.2. Motivation for a review of studies on the relationship between environmental lead and blood lead ir^ children The relationship between environmental lead exposure and the concentration of lead in blood has been reviewed recently by several authors (Hammond et al. 1981, Ratcliffe 1981, Snee 1981, Chamberlain 1983a, Jones and Stephens 1983). These reviews have concentrated on the relationship between air lead and blood lead in adults and only limited attention was paid to studies among children. The focus was on air lead in these reviews, and minimal attention was paid to the role of ingestion of soil and dust particles by children as a mode of lead intake from the environ• ment. As a result, most reviews have assumed that the impact of environmental lead on blood lead is not much larger for children than it is for adults. When it was suggested that this point of view should serve as a basis for the development of air quality standards for lead (Snee 1982a), the author has commented that a re-evaluation of childhood blood lead studies might result in a higher estimate of the impact of environmental lead on children's blood lead (Brunekreef 1983). Subsequently, it was decided to review the relationship between environmental lead and blood lead for children in detail, stressing the importance of non-inhala• tion modes of lead intake from the environment by children. 0.3. Background of environmental impact study in Rotterdam, The Hague and Zoetermeer In the spring of 1979, blood lead levels were measured in a number of Dutch child populations of nursery school age, within the framework of the First E.C. Blood Lead Survey (Ligeon et al. 1981). In the city centers of Rotterdam and The Hague, children were found to have blood lead levels which slightly exceeded a guideline which was used by the Dutch Department of Public Health to evaluate the results of the Survey. In this guideline, it was 2 stated that at least 50% of blood lead levels found in any popu• lation of children had to be less than 20 ug/100 ml, 90% less than 25 ug/100 ml and 98% less than 30 ug/100 ml. The 90- and 98- percentiles of this guideline are 5 iig/100 ml lower than the Biological Quality Guide for the concentration of lead in blood proposed by Zielhuis (1974) and adopted by the E.C. (E.C. 1977) for the general population; the fact that children are more susceptible to lead than adults was the main reason to use a lower guideline. In the spring of 1981, a Second E.C. Blood Lead Survey was to be held. At the request of the Department of Public Health, an environmental exposure study was conducted in conjunction with the Survey, to investigate to what extent the elevated blood lead levels in inner city children could be explained by exposure to lead in the environment. The study was designed on the basis of our earlier work in Arnhem, where the surroundings of a secondary lead smelter were studied in 1978, to assess the intake routes of lead from the environment by preschool children (Brunekreef et al. 1978, 1981, Diemel et al. 1981). In the Arnhem study, significant associations between some lead exposure variables and children's blood lead levels were found although the general level of environmental lead exposure was low in the study area (when compared to results from smelter studies performed abroad), and although blood lead levels were not higher than in Dutch inner city children in 1979. It was therefore considered possible that the elevated blood lead levels in the inner city children of Rotterdam and The Hague were also related to exposure to lead in the environment.