Dissipation of environmental DDT and its metabolites in selected rivers of south-western Kenya

Rivers are the main source of domestic and industrial water supplies in Kenya. In this study, water sampling was done at eight upstream sites in the Kuja River catchment, Kenya, between October 2016 and April 2017, specifically to test for residue levels of the organochlorine pesticide, dichlorodiphenyltrichloroethane (p,p′-DDT), and its degradation products, dichlorodiphenyldichloroethylene (p,p′-DDE) and dichlorodiphenyldichloroethane (p,p′-DDD). The analysis was performed with gas chromatography coupled with electron-capture detection in an autosampler. Concentrations of these residues in the surface water samples ranged from below detection limit (BDL) to 1.1113 μg l-1 in the wet season, and from BDL to 2.007 μg l-1 in the dry season. Overall, the highest mean residue concentration was for p,p′-DDT (0.9669 ± 0.2994 μg l-1). The lowest mean concentration in the dry season was that of p,p′-DDE (0.1824 ± 0.0964 μg l-1), and in the wet season it was p,p′-DDD (0.0610 ± 0.0038 μg l-1). From our results it is evident that DDT is still in use and detectable in the study area, though the mean levels detected were below the acceptable thresholds for natural water as suggested by the World Health Organization (WHO). Except for a slightly higher mean spatial distribution of the metabolite p,p′-DDT, the resides were recorded as below the maximum admissible concentrations of pesticide residues in drinking water, as set out in WHO guidelines and by Kenya’s National Environment Management Authority (NEMA). Monitoring organochlorine pesticide contamination levels in Kenya’s water resources should be scaled up to leverage potential for a sustainable blue economy and in safeguarding human and environmental health.