Centennial-scale evolution, source apportionment, and ecological risks of heavy metals in Daya Bay, South China sea

Heavy metal (HM) pollution in estuarine and coastal environments has become a significant issue, particularly with frequent anthropogenic activities. This study aims to investigate the chronological sequence of sediment cores from Daya Bay and explore the spatiotemporal variation, pollution sources, and ecological risks of eight HMs (Fe, Cu, Zn, Pb, Hg, Ni, Cr, and Mn). The results indicate that the sedimentation rate in the western nearshore area ranges from 0.59 to 0.74 cm/yr, and a similar temporal variation pattern is observed for the concentrations of these HMs. Non-metric Multidimensional Scaling (NMDS) analysis revealed a regime shift in the sedimentary system during the 1980s, along with an increase in potential ecological risk levels. Human activities have increasingly intensified the negative impact on the ecological environment of the bay, primarily driven by a combination of pollution sources, including traffic emissions, industrial processes, natural processes, and aquaculture activities. Comprehensive toxicological risk assessments identified Hg, Cu, Cr, and Pb as priority elements for aquatic exposure risks, with Hg contributing the highest individual risk, especially in the northwestern sea area. The probability of adverse effects from HM mixtures on aquatic biological communities in the three sampling regions were 23.6 %, 8.7 %, and 30.2 %, respectively. These findings provide valuable data to support the management and remediation of HM pollution in coastal sedimentary environments.