Exploration of different methods for measuring DDT exposure among malaria vector-control workers in Limpopo Province, South Africa

Abstract

DDT compounds are used in many developing countries, including South Africa, for the control of malaria vectors. This study investigated biological exposures among workers in relation to job history. A cross-sectional study of 59 workers at the Malaria Control Centre (MCC) in Tzaneen, South Africa, was performed. Tests included a job history questionnaire and the measurement of serum o′ p′ and p′ p′ isomers of DDE, DDT, and DDD, corrected for serum total lipids. Forty-seven (80%) workers donated a blood sample for the determination of serum DDT. The mean number of years worked at the MCC (malaria years) was 15.8±7.8 years and the mean serum DDT was 94.3±57.1 μg/g of lipid. There were no significant associations between short-to-medium-term serum DDT exposure measures ( o′ p′-DDE and o′ p′ and p′ p′ isomers of DDD and DDT) and malaria years. The long-term exposure measure, p′ p′-DDE, was significantly associated with malaria years ( β ̂ =3.0±1.2 μg/g lipid/year; P=0.001; n=47; adjusted for age), but only 27% variance of p′ p′-DDE was explained. Blood total DDT uncorrected for lipid content was strongly related to corrected levels ( β ̂ =0.74±0.48 , P=0.00, R 2=0.77), but uncorrected p′ p′-DDE had a weaker association ( β ̂ =0.0024±0.0013 , P=0.074; R 2=0.53) with malaria years than did corrected levels ( β ̂ =0.042±0.017 ; P=0.016; R 2=0.56). The results show that serum DDT levels for malaria vector-control workers in South Africa with a long-term spraying history are high. Job history information on DDT exposures must be very detailed in order to provide valid estimates of exposure.