Rapid changes in organochlorine pesticides in sediments from the East China sea and their response to human-induced catchment changes.

Human-induced catchment changes have affected the sedimentary processes in marginal seas, which will impact the transport and burial processes of materials and inevitably impact marine biogeochemical cycles. Organochlorine pesticides (OCPs) and sediment characteristics in surface sediments from the East China Sea (ECS) at two time points (2006 and 2018) were compared to understand the response of OCPs to human-induced catchment changes. A significant coarsening trend occurred after the impoundment of the Three Gorges Dam (TGD), with the mean grain size increasing from 6.4 ± 1.2 Φ to 4.4 ± 2.1 Φ, suggesting that the sedimentary environment in the ECS changed drastically. OCP concentrations in the ECS evidently decreased after the impoundment of the TGD, with mean values decreasing from 2.55 ± 1.51 ng g to 1.08 ± 0.84 ng g. The deposition flux of OCP also decreased from 2.65 ± 1.67 ng cm yr to 0.89 ± 0.60 ng cm yr. The reduction in the riverine input might be the reason that caused variations in the OCP concentration and deposition flux. In addition, sediment coarsening is likely to be the another primary factor influencing the differences in the distribution and deposition flux of the OCPs in the ECS. Therefore, the distribution and burial of OCPs in the ECS have been changed drastically, which may broadly impact the marine environment and biogeochemical cycles.