A study of the distribution of urban environmental lead levels in Cape Town, South Africa

Epidemiological studies which have attempted to quantify the relationship between environmental lead and blood lead levels have been beset by numerous methodological problems, one of which has been the difficulty in assessing environmental exposure to lead. In Cape Town, South Africa, a comprehensive environmental lead monitoring programme was instituted in an inner city suburb where a blood lead screening study was in progress. The objective of the study was to examine the spatial and temporal variation in environmental lead levels, and to examine the role of potential influencing factors such as traffic. Results revealed substantial intra-urban variations in air lead levels, with annual means varying from less than 0.5 to over 2 μg/m3 at individual sites. Traffic density and the distance from heavily trafficked roads were important influencing factors within the area. Considerable seasonal as well as daily variations in air lead levels were also documented, and air lead levels were positively associated with dust lead levels. The spatial and temporal variations in environmental lead have implications for air monitoring strategies and epidemiological studies concerned with the relationship of exposure to lead and the health impact on populations. Micro variations in exposure need to be taken into account in assessing exposure to environmental lead in epidemiological studies, in light of the considerable variations which may occur.