Assessment of Organochlorine Pesticide Residues in Water, Sediment, Soil and Khat (Catha Edulis) in Igembe South, Meru County, Kenya

Abstract

Organochlorine pesticides (OCPs) are highly persistent in the environmental media including soil, water, and air, and are also widely detected in food materials. High levels of OCPs are associated with diverse ill health effects that include carcinogenicity, teratogenicity, endocrine disruption, immune system suppression, and environmental degradation. There is inadequate data on the extent of OCPs contamination in Igembe South sub county. Hence, the aim of this study was to determine the organochlorine pesticide residues levels in water, sediments, soil and khat from selected points in Igembe south in Meru County where khat has been cultivated over the years. The study was guided by interviews using structured questionnaires to gain data on the kind of pesticides applied in the area. Thereafter, field sample collection and testing of khat, sediments, water, and soil samples to determine organochlorine pesticide residue levels was carried out. Soil and khat were sampled from farms where khat is grown, while sediments and water sampling done from the Ura river traversing the farms. Soxhlet method was applied during extraction of pesticides from soil, sediments and khat samples while solvent-solvent extraction method applied to extraction from the water samples. The extracts were cleaned by eluting with HPLC grade n-hexane through preconditioned aluminum oxide chromatographic column and concentrated using a rotary evaporator and further concentrated under a stream of nitrogen to 500 μL. Samples were analyzed for presence of 17 OCPs using a gas chromatograph equipped with an electron capture detector. The mean values of physicochemical parameters of River Ura water ranged between 6.7±0.04 and 7.8±0.04 for pH, 48±0.58 to 167±1.15 μS/cm for electrical conductivity and 25±1.15 to 88±1.00 mg/L TDS levels. The mean residue levels of organochlorine pesticides in the soil samples collected ranged from <0.001± 0.00 - 197.07±36.47 μg per kg with the highest recorded in soil samples from Anchenge sampling site in March 2016. In water, pesticide residue levels varied from <0.001± 0.00 to 5.64±0.99 μg/L with the highest levels recorded in water samples collected from Kiiji site in March. The sediment samples had pesticide residue levels varying from <0.001 to 134.96±24.36 μg/kg and the highest concentration was in sediment samples from Ikandu site collected in March. In the khat samples, concentrations ranged between <0.001 - 110.11±5.31 μg/kg. According to the findings, environmental samples from the Igembe South sub-county still contain DDT and its metabolites, heptachlor, aldrin, dieldrin, endrin, lindane, and other pesticides that have been banned. Organochlorine pesticide concentrations varied widely in water, soil, sediment, and khat. The variances were caused by differences in the site's locations, human activities, seasonal variations and environmental factors.