Vertical migration of short– and medium–chain chlorinated paraffins in the marine water column and sediments of the Northern Yellow Sea, China

Short– and medium–chain chlorinated paraffins (SCCPs and MCCPs) are high–production–volume persistent organic pollutants, attracting increasing global concerns. Coastal zones are suffering severe adverse impacts from SCCPs and MCCPs derived from both terrestrial discharge and marine anthropogenic activities. However, data on their occurrence, and vertical transport mechanisms within marginal sea systems remain sparse and their sources and ecological risks in marine ecosystem are poorly understood. Herein, the spatial distribution and vertical migration of MCCPs and SCCPs in surface, bottom seawater, and sediments of the Northern Yellow Sea (NYS) were systematically investigated. Results identify maritime discharge from shipping lanes and inputs from aquaculture as the primary contamination sources. Both MCCPs and SCCPs were ubiquitously found across all samples, with higher levels of SCCPs than MCCPs in sediments. Bottom seawater exhibited higher CP concentrations than surface seawater, attributing to the hydrophobicity–driven sorption to suspended particles and subsequent settling/resuspension processes. Sediment–water partitioning and fugacity fraction ( ff ) analyses indicated congener–specific behavior played a key role in the vertical migration of CPs. Most CP congeners showed low ff values (<0.2), confirming sediments as a primary sink, whereas congeners with shorter carbon chain and lower chlorine substitution (e.g., C 10 Cl 5 ) displayed a potential for remobilization, with a mean ff value of 0.897. Ecological risk assessments revealed a medium risk in seawater, and a low but persistent risk in sediments. These findings highlight the critical roles of hydrodynamics, organic matter, and marine anthropogenic emissions in governing CP fate in the NYS coastal zones.