Spatial and temporal distributions of sedimentary polycyclic aromatic hydrocarbons at a deep-sea waste dumpsite in the East Sea, Korea: Implications for ocean dumping regulations.

Ocean dumping of sewage sludge at the East Sea "Byeong" (ES-B) deep-sea disposal site was prohibited in 2016 under strengthened national and international regulations. This study presents the first long-term assessment of polycyclic aromatic hydrocarbons (PAHs) at ES-B using surface sediments (2009 and 2022) and sediment cores (2013 and 2019) from eight stations. Temporal changes in PAH concentrations, composition, sources, and ecological risk were examined to evaluate the effects of dumping cessation. Σ27PAHs in surface sediments declined by 25-89% between 2009 and 2022, with the largest reductions at historically impacted stations such as DB085, reflecting higher initial contamination levels associated with past dumping activities. Concurrent shifts in δ13C, C/N ratios, and perylene/Σ27PAHs indicate reduced terrestrial inputs and ongoing natural attenuation after dumping ceased. A sediment core from the central depositional zone (DB089) records strong anthropogenic PAH enrichment during active dumping that weakens toward the surface by 2019, consistent with burial and dilution by cleaner post-ban sediments. The core provides a local temporal record that complements the broader decline in PAHs observed across the surface sediments. Source apportionment identified three dominant PAH sources: mixed, petrochemical combustion, and incineration combustion. Anthropogenic contributions decreased from ~94% in 2009 to ~54% in 2022. Ecological risk declined accordingly, with PAH mERM-Q values decreasing from 0.05 to 0.02, and the value at DB085 decreasing from 0.14 to 0.014. These results suggest an improvement in sediment quality at the ES-B site following the dumping ban and support continued monitoring to ensure the long-term protection of the benthic ecosystem.