Abstract:
The occurrence, concentration and spatial distributions of Endosulfan (6,7,8,9,10,10-hexachloro-
1,5,5a,6,9,9a-hexahydro–6,9-methano-2,4,3-benzodioxathiepine-3-oxide) and endosulfan sulfate were
studied in the Lake Naivasha basin during the months of May to December 2010. The aim of the study
was to determine the concentration of endosulfan in the watercourse. Endosulfan sulfate was the most
predominant with a range of 16.2 - 345 ng/L and a mean of 131 ± 110.2 ng/L followed by endosulfan II
41.7 – 92.8 ng/L and a mean of 60.6 ± 20.3 ng/L, and endosulfan I 20.1 – 57.9 ng/L and a mean of 34.3 ±
14.7 ng/L respectively. The measured exposure concentrations were translated into environmental risks
factors using the PERPEST model Version 3.0. The model was calibrated using laboratory experimental
data on exposure of O. leocostictus to endosulfan in aquariums simulating Lake Naivasha. The
environmental risks posed by the measured exposure concentrations of endosulfan on O. leocostictus
were predicted as total endosulfan (ΣEndosulfan). ΣEndosulfan ranged from 80.9 - 450 ng/L within the
basin with a mean of 225.8 ± 129.1 ng/L. Results of the prediction were compared those obtained from
microcosm laboratory experiments simulating the Lake Naivasha ecosystem to assess the accuracy of
the model. The study shows that though the insecticide is not targeted to kill fish it has an adverse
effect on the population of O. Leocostictus. The measured exposure concentrations can cause reduction
in population of O. Leocostictus by between 0 – 6% in O. Leocostictus. Comparison of the results of the
prediction shows that there is no significant difference between the results obtained from the
microcosm experiment at p = 0.05. The study shows that the model can be applied in environmental and
toxicity studies of chemicals without the use of laboratory specimens. The study also explains the
variability of aquatic organisms’ populations in the lake can explain the current decline in populations of
aquatic life in Lake Naivasha. Increased monitoring is thus recommended to detect inflow of toxic
chemicals to safeguard aquatic life.
