Semi-centennial sediment records of HCHs and DDTs from the East China marginal seas: Role of lateral transport in catchment.

We reconstructed the history of the inputs of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) into the marine environment to reveal the time-dependent influence of sources and associated anthropogenic activities in China, based on Pb-dated cores from the East China marginal seas (ECMS). The temporal dynamics of pesticide contamination expresses as deposition fluxes, inventories, and half-life estimations varied among the cores, suggesting heterogeneity in transport pathways of pollutants. The depth profiles of pesticide inputs closely followed their historical production and application timelines in China, and were also affected by human activities in catchments, with general declines in HCH and DDT inputs to the coring sites after their peak deposition. Despite the prevalence of occurrence of weathered HCH/DDT in the cores, there were clear source-dependent differences in isomeric composition and accumulation between before and after these pesticides were banned. α-HCH and p,p'-DDT were relatively more enriched in sediments from the pre-ban period when heavy technical HCHs and DDTs use occurred, as indicated by the higher α-/β-HCH and lower (DDE + DDD)/DDTs ratios, and the larger fractions of α-HCH and p,p'-DDT influxes to the coring sites in the ΣHCH and ΣDDT fluxes, respectively, while this pattern shifted to be historical residue-based in the post-ban period. The difference in the recent influxes of pesticides to core sediments and their higher post-ban inventories highlight the increasing importance of historical sources over time and continuous input of weathered residues into marine environment via lateral transport.