Persistent heavy metal contamination at the East Sea-Byeong dumping site: Tracing the impacts of ocean dumping and policy changes over two decades.

This study investigated the spatiotemporal dynamics and persistence of heavy metal contamination at the East Sea-Byeong (ES-B) dumping site, focusing on environmental responses to policy shifts that phased out land-based waste disposal. We integrated a time-series analysis of heavy metal input loads (1991-2015) with surface sediment monitoring (2006-2021), complemented by a 3D particle-tracking model and various geochemical indices (e.g., Igeo and mCd). Heavy metal input loads increased substantially and peaked in 2005, reaching 15-80 times the 1991 levels, before declining by 96-99% by 2015 following the implementation of the "Zero Ocean Dumping" policy. Despite the sharp reduction in inputs, heavy metal concentrations remained elevated at several resting-area stations through 2021, indicating persistent contamination in historically impacted hotspots. Particle-tracking results, derived from waste-specific settling properties, were broadly consistent with the observed spatial variability. Correlation analyses showed weak associations between heavy metals and Al, Fe, and grain size, while several metals were positively correlated with TOC, consistent with substantial anthropogenic inputs associated with historical waste disposal. Regional-background-based indices (CF, Igeo, PLI, and mCd) provided the clearest representation of spatial and temporal contamination patterns, whereas mPELq primarily reflected potential combined toxicity relative to sediment-quality guidelines. Overall, the results demonstrate that contamination can persist for decades after substantial reductions in waste inputs, highlighting the need for site-specific risk assessment, targeted management of persistent hotspots, and sustained environmental monitoring at legacy deep-sea dumping sites.