Spatial distribution of persistent organic pollutants in the surface water of River Brahmaputra and River Ganga in India.

Persistent organic pollutants (POPs) like organochlorine pesticides (OCPs), polychlorinated biphenyles (PCBs) and polyaromatic hydrocarbons (PAHs) are discharged in surface water by various point and nonpoint sources thereby degrading the functioning of the ecosystem and threatening human health. Chlorinated pesticides such as Hexachlorocyclohexane (HCHs) and Dichlorodiphenyltrichloroethane (DDTs) are effective pest control chemicals, used in agriculture and public health activities (malaria eradication, etc.) in India for the past several decades and are still in use. POPs can cause endocrine disruption and food chain biomagnification because of their lipophilicity and environmental persistence. This study aims to assess the environmental occurrence and spatial distribution of OCPs, PAHs and PCBs in the surface water of River Brahmaputra and Ganga ending at the of the Bay of Bengal.The order of organochlorine pesticides is as: heptachlor>HCHs>DDTs>dieldrin>aldrin>endosulfan. Diamond Harbour and Bakkhali were the two places with elevated level of all individual HCH isomers compared to all other sites. β-Endosulfan and α-Endosulfan were high at Dibrugarh than other sampling sites. This is due to the ongoing use of Endosulfan in the tea estates in Assam especially the estates close to the town of Dibrugarh. p,p'-DDT and o,p'-DDT levels indicate the fresh input of DDT in all the sampling sites. Heptachlor has been observed in 57% of the total samples reported in the present study.These reasons may attribute to high deposition of pesticides in the surface water of Ganga and Brahmaputra.In addition the catchments area of the Ganga River is surrounded by agricultural lands so a relatively higher residue of pesticides was prevalent. Σ27 PCBs varied from BDL to 142 (Avg±SD, 3.96±6.71) ng L-1. PCB-18, PCB-52 & PCB-44 showed the highest concentration levels for all the sampling sites. PCB-126 was observed in samples taken from sites close to the city limit of Kolkata and Assam which is an indication of higher toxic effect from this highly toxic congener. PCB-169 was prevalent in most of the sites. The total concentrations of PAHs varied from BDL to 31 (Avg±SD, 0.2±1.5) µg L-1. PAHs concentrations were very low as PAHs are particle bound compounds.