Assessment of organochlorine Pesticides residues in water and sediments From mutuini, Nairobi and Kangemi dams in The Nairobi River Basin
Wanyama, Nandokha George
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Nairobi is prone to a wide variety of uncontrolled activities, varying in scope, time span, material input and environmental emission. New chemical inventions and applications are expected to generate more pollutants that may be washed into the Nairobi River Basin. Despite these ever changing trends, the rate of generation of statistical data about such trends is not concurrent. Previous use of certain Organochlorine pesticides for pest control has caused serious problems due to their persistence in the environment, potential toxicity and bioaccumulation (Kanja et ai, 1998). Because of these factors, many countries have banned or restricted the use of OCPs. In the past, Kenya used DDT to control ticks and malaria pests, especially in the mosquito infested areas (Kanja et al., 1998). Of late, typical examples of exposure have been demonstrated, such as the detection of p,p'DDT, p,p'DDE, p,p'DD, Dieldrin and Lindane in breast milk of Nairobi women (Kanja, 1998) and in drinking water in Central Kenya (Mwanthi, 1998) A study was undertaken to investigate the temporal and spatial distribution of 17 OCPs residues namely: aldrin, a-hexachlorocyclohexane, ~- hexachlorocyclohexane, y- hexachlorocyclohexane 8- hexachlorocyclohexane, p,p' -dichloro-diphenyl-tricWoro-ethane, 1,I-dichloro-2,2-bis4- chlorophenyl-ethane, 2,2-bis p-chlorophenyl 1,l dichloroethylene, dieldrin, endosulphan I, II, and the sulphate isomer, endrin, endrin aldehyde, heptachlor, heptachlor-epoxide, and methoxychlor in water and sediments from Nairobi, Mutuini and Kangemi Dams of the Nairobi River Basin. A total of 54 water and 54 sediment samples were collected monthly for 6 months from December 2009 to May 2010 and anal,?ed/using Gas chromatography. Physico-chemical parameters; pH, Total Suspended Solids, Total-Dissolved Solids, Electrical Conductivity, Total Organic and moisture Carbon were also determined to establish their co-relationship with concentration of pesticides. The influence of season to season changes on concentration of pesticides on Mutuini, Nairobi and Kangemi dams ,was also established. All OCPs were present in all the samples analyzed although Heptachlor. and Methoxyhlor were below detection limits. y-HCH, endrin aldehyde, heptachlor and methoxychlor were below detection limit in water from all the three sampling sites. In sediments, mean OCPs residues ranged from BDL to 16.99±0.99 ng/g recorded for endosulphan I in May at Mutuini Dam during the long rains season, and from BDL to 23.74±4.43 ng/L in water, recorded for o-HCH at Mutuini Dam in March during the long rains season. Sediments were more contaminated with OCPs as compared to water. Mutuini Dam showed more OCPs prevalence followed by Nairobi Dam then Kangemi Dam. The Pearson correlation between OCPs concentrations and levels of pH in water samples (N=6) : were 0.72, 0.77 and 0.53 for Kangemi Dam, Nairobi Dam and Mutuini Dam respectively and -0.32, -0.28 and 0.54 for Sediments, respectively. Pearson correlations between OCP concentrations and all other physico-chemical parameters were either positive and insignificant or negative ... The levels of the determined pesticides were below WHO guidelines for drinking water. There is still a risk of human exposure to pesticides because of their ability to bioaccumulations through the food chain. This study serves as a guide for monitoring programs of the Kenya, government to achieve its commitment to Stockholm Convention and to extend focus on current pesticide applications besides the banned OCPs.