Particle-associated distribution, sedimentary accumulation, and SSD-based ecological risk assessment of organochlorine pesticides in the East China Sea.

Although legacy and emerging organochlorine pesticides (OCPs) are the main contaminants of concern in Chinese marginal seas, their distribution and occurrence in suspended particulate matter (SPM) remain poorly characterized. In this study, we investigate 11 OCPs in the East China Sea (ECS), including seven legacy and four emerging OCPs. The concentrations of Σ11OCPs in SPM ranged from 0.05 to 0.55 ng/L, while those in sediments varied from 276 to 395 ng/g dw. Spatially, Σ11OCPs in SPM exhibited a general distribution pattern of nearshore enrichment and offshore decline, while sedimentary Σ11OCPs concentrations were relatively higher in the northern and southern sectors of the study area. Among legacy OCPs, Heptachlor and its epoxides were the dominant compounds, while emerging OCPs, particularly Oxyfluorfen, Nitrofen, and Dicofol, contributed substantially to sediment inventories and sedimentary fluxes, indicating the increasing importance of contemporary inputs. Diagnostic ratios, principal component analysis, and positive matrix factorization consistently suggested that OCPs in the ECS originated from mixed agricultural sources and historical legacy sources. Species sensitivity distribution-based risk assessment indicated overall low acute ecological risks in both SPM and sediments, although Heptachlor, Oxyfluorfen, and Nitrofen were identified as the major contributors to risk. These findings reveal that legacy OCPs remain an important pollutant class in the ECS, while emerging OCPs are becoming increasingly abundant, underscoring the need for sustained monitoring of their source inputs and long-term ecological effects.