Spatial distribution and temporal trend in concentration of carbofuran, diazinon and chlorpyrifos ethyl residues in sediment and water in lake naivasha, Kenya

Chlorpyrifos ethyl was found to be widely distributed in water and sediment in Lake Naivasha. Higher levels were reported in sediment (11.2-30.0 ng g-1 dry weight (dw) in wet season than in dry season (4.7-17.4 ng g-1 dw). The mean concentration of chlorpyrifos ethyl in water in wet season ranged between 8.8 and 26.6 lg L-1 and decreased to between below detection limit to 14.0 lg L-1 in dry season. On average, higher concentrations of chlorpyrifos ethyl were observed in sediment than water samples. Statistical analysis revealed a significant difference in concentration between the seasons, and a significant interaction between seasons and mean concentrations at p B 0.05. However, levels of diazinon and carbofuran were below the detection limit in all the samples analyzed. Notably, levels of chlorpyrifos ethyl were higher than the maximum allowable limits (0.1 lg L-1) recommended by European Union for drinking water and general water quality criterion for protection of freshwater water organisms (0.083 lg L-1).