Spatial distribution and source characteristics of legacy and emerging antifouling residues in surface sediments of Gohyeon Harbor, South Korea.

Biocidal additives used in antifouling paints are important contaminants in harbor environments due to their persistence and potential ecological impacts. Organotin compounds (OTs) were historically used as highly effective antifouling agents, whereas various booster biocides (BBs) have been introduced as alternatives following the global ban on tributyltin (TBT)-based paints. This study investigated the concentrations, spatial distribution, and potential sources of OTs and BBs in surface sediments from Gohyeon Harbor, a semi-enclosed harbor on the southern coast of South Korea surrounded by shipyards, aquaculture facilities, and agro-industrial complexes. Butyltin concentrations ranged from 35.8 to 852 ng Sn g-1 dw, with TBT ranging from 0.34 to 196 ng Sn g-1 dw. TBT and dibutyltin were elevated near shipyard sites, indicating that legacy inputs from shipbuilding and maintenance activities remain the dominant source. In contrast, monobutyltin exhibited higher concentrations in the outer harbor, where aquaculture facilities are located, suggesting inputs from aquaculture-related materials rather than only TBT degradation. BBs also exhibited distinct source patterns: Diuron and Irgarol were associated with shipyard activities, whereas dichlofluanid and DCOIT showed relatively high concentrations in areas influenced by aquaculture and land-based industrial inputs. Although TBT concentrations have declined following global regulations, relatively high levels persist in harbor sediments, indicating ongoing legacy contamination. Elevated dichlofluanid and DCOIT concentrations may reflect the increasing use of alternative BBs, as well as contributions from aquaculture facilities and surrounding land-based sources.