EXAMINING THE ASSOCIATION BETWEEN MANGANESE AND LEAD BLOOD LEVELS IN SCHOOLCHILDREN IN FOUR SELECTED REGIONS OF SOUTH AFRICA

Abstract

ISEE-404 Introduction: In South Africa, anthropogenic sources of manganese (Mn) and lead (Pb) derive primarily from industrial activities and vehicular emissions of petrol additives. At elevated levels, both metals are neurotoxic, with manganese being also an essential nutritional element. Aim: The aim of this study was to assess the possibility of synergistic effects of manganese and lead in four groups of schoolchildren residing in different geographical regions of South Africa. A number of recent studies showed a relationship between blood levels of manganese and lead. Methods: A cross-sectional survey was carried out in schools of three cities [Cape Town (11 schools), Johannesburg (10 schools), Kimberley (6 schools) and in the Northern Cape in three rural sites, one being a lead mining town (4 schools)]. Schools were the primary unit of sampling and the total number of venous blood samples collected from grade one children was 1282. Both blood and environmental samples collected at schools were analysed for Mn and Pb levels. A structured questionnaire was administered to the parents/guardians of study children to obtain essential background and risk factor data. The relationships between blood manganese and blood lead levels (treating each in turn as the response variable in order to adjust for the effect of confounding variables) were investigated by fitting mixed models. All statistical analyses were carried out using Stata release 8 (Statacorp. 2003). Results: Mixed models were fitted with log (manganese concentration) as the response variable, and blood lead level as the principal explanatory factor. The model also included terms for centre and a centre by lead interaction and examined potential confounders. The important confounders were found to be gender, race, paint peeling from the inside walls of the house and pica. There was a significant centre by lead interaction (P<0.0001), with the effect of lead being different in the various centres - thus we cannot conclude that there is an overall association between log (Mn) and blood lead level. Mixed models fitted with blood lead level as the response variable and blood manganese as the principal explanatory factor, with terms for centre, a centre by manganese interaction and potential confounders, again found overwhelming evidence (P<0.0001) of a centre by manganese interaction. This confirmed that there is no consistent relationship between the two metals examined. Conclusion: Previous studies found a relationship between lead and manganese levels in blood. In our study in four centers we found great variability in both blood lead and manganese levels, both within and between sites. However there was no consistent relationship between the two metals over the four sites.