Risk assessment for organochlorines and organophosphates pesticide residues in water and Sediments from lower Nyando⁄Sondu-Miriu river within Lake Victoria Basin, Kenya

Abstract

The objective of this study was to survey and document pesticide residue levels in the lower Nyando ⁄ Sondu-Miriu catchment areas of Lake Victoria, Kenya, during the dry and rainy seasons of 2009. Water and sediment samples from the Nyando ⁄ Sondu-Miriu Basin were analysed for selected pesticide residues, using gas chromatography equipped with Ni63 and CP-SIL 8CB-15m and TSD detectors for organochlorine and organophosphorus pesticide residues, respectively. The findings indicated that banned organochlorines are still being used in the catchment. Dieldrin and p,p¢-DDD were notably higher (P < 0.05) in concentrations than their metabolically formed analogues of aldrin and DDT, respectively. Notably, organophosphorus was below detection levels in water samples, whereas diazinon and malathion were at higher levels in sediment samples. The total residues of DDT, HCH, methoxychlor and endrin generally were below WHO drinking water limits of 2, 2, 20 and 0.01 lg L)1 , respectively, whereas aldrin and dieldrin were above the recommended values of 0.03 lg L)1 . Agricultural activities in the Lake Victoria Basin are influencing accumulation of the pesticide residues in the basin rivers and the lake. The study recommends creation of buffer zones around the natural water bodies to reduce the inflow of pesticides into water bodies. An integrated pest management approach that encourages reduced usage of chemical compounds also should be encouraged.