Contamination profile of DDT and HCH in surface sediments and their spatial distribution from North-East India

• DDT and HCH levels in sediments are higher in ponds/wetlands in India as compared to rivers/streams.
• DDT and HCH levels are positively associated with total organic carbon and clay and silt contents.
• DDT and HCH levels exceeded sediment quality guidelines in most sediment.
• Residue levels of DDT and HCH have originated from historical and recent usage.

Contamination status and spatial distribution of DDTs and HCHs were investigated in sediments collected from ponds and riverine system from districts Nagaon and Dibrugarh, North East India. A total of 113 surface sediment samples were collected from both the districts including 43 from ponds/wetlands and 70 from rivers/streams. Based on dry weight (dw), the mean concentration of ∑HCH and ∑DDT in sediments were found to be 287 ng/g (71.2–834 ng/g) and 321 ng/g (30.1–918 ng/g) for district Dibrugarh while 330 ng/g (39.2–743 ng/g) and 378 ng/g (72.5–932 ng/g) for district Nagaon, respectively. DDTs and HCHs in sediments were well influenced by total organic carbon, clay and silt content of sediments. Source identification revealed that sediment residue levels have originated from long and recent mixed source of technical HCH and Lindane for HCHs and mainly technical DDT for DDTs. Majority of samples exceeded the sediment quality guidelines (SQG) for γ-HCH, p,p′-DDT and ∑DDT indicating potential environmental risk. This baseline data can be used as reference for regular ecological and future POPs monitoring program.