Environmental lead exposure among inner-city Cape Town children : a study of associated risk factors

Doctoral Thesis


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University of Cape Town

Risk factors for lead exposure among children in South Africa have not been well documented. This study elucidated important factors which co-vary with lead in increasing children's risk of exposure. Two study designs were used. First, a cross-sectional analytical study involving first grade school children was executed. Venous blood samples from children were analysed for lead using atomic absorption spectrophotometry. In addition other haematological and anthropometric measurements were conducted. A pre-tested questionnaire administered to parents identified risk factors for lead exposure. Statistical analyses, including log-linear models, were used to determine the relationships between biological, environmental, social factors and blood lead. In an environmental study, daily air and dust samples were collected over a year from several sites in the study area, contemporaneously with the blood and questionnaire surveys. Spatial and temporal variations in atmospheric lead were determined. In stage two a case control study was carried out to determine whether risk factors for lead exposure differed among cases (blood lead ≥ 24 ug/dl) and controls (blood lead ≤ 14 ug/dl). Levels of lead in air, water, paint and dust samples from children's homes were determined and the state of housing evaluated. Home interviews were conducted with parents to assess the role of economic, demographic, cultural, and behavioural factors in increasing children's risk. 13% of coloured children, but no white children were identified with blood lead levels ≥ 25 ug/dl. Air lead levels ranged from< 0.5 ug/m³ to> 1.5 ug/m³ and dust lead levels from< 550 ppm to> 3 000 ppm. Environmental lead levels were significantly elevated near heavy traffic, particularly during winter months. Baseline exposure was of significance in influencing blood lead levels of children attending schools in direct proximity to heavy traffic, where blood lead levels were elevated. In cases, direct inhalation of aerosols, and ingestion of lead in water were not found to be important risk factors. Hand contamination and mouthing were associated with increased risk. Sources of elevated lead were found in the homes of both cases and controls, but were not accessible in the homes of controls. A conceptual framework for lead exposure in children is proposed, to illustrate how social and environmental factors may act to increase risk. The results have implications for primary and secondary prevention strategies aimed at the community.

Bibliography: pages 284-306.