Abstract

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High concentration of pesticides was found in the sediment of river Yamuna. This can be attributed to the excessive use of pesticide in agriculture and health purpose. The distribution of various organochlorine pesticides in the sediments from 12 sampling sites reveals a wide range of fluctuation. Results indicated that although these pesticides are banned in India but still used by farmers due to their cheap costs.
The distribution of pesticide is not found uniform and they did not follow a single pattern. It may be due to the physico-chemical properties of pesticide as well as the sediment properties. Further, hydrophobicity and persistence of these pesticides increases the accumulation in sediments. The main sources of pesticides in sediments are agricultural runoff, aquaculture activities and atmospheric deposition. The isomeric composition of HCH reveals a heterogenic nature of distribution in the sediments. This may be relative to isomerization of HCHs during the processes of transport and transformation in an aquatic system. The T-HCH ranges from 274 to 405 μg/Kg in the sediment of river Yamuna, Agra, in which α-HCH was 188±56 μg/Kg in the upstream cis Yamuna and 150±2 μg/Kg in the cis Yamuna downstream, while γ-HCH was 84±13 μg/kg in the upstream and 101±19 μg/Kg downstream of cis Yamuna. But the concentration of α-HCH was 173±5 μgm/kg at upstream and 165±34μgm/kg at downstream, whereas γ-HCH was 92±20μgm/kg in upstream and 93±12 μgm/kg at downstream trans Yamuna sediment at Agra. γ-HCH and α-HCH were found higher in concentration at many places and has a good relation with a composition of technical grade HCH, which contains 70% a-HCH and 14 % γ-HCH, rest is β and δ isomers. Further, (isomers of α, β and δ are observed to contribute about 33-74%, 28.5% and 26-50% respectively, to the total HCHs. ?-HCH has higher values of Hennery Law constant and vapour pressure than β and γ-HCH, indicating greater efficiency by atmospheric transport of α-isomer than other isomers). These factors may account for the α-isomer existing in all samples.

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