Spatiotemporal Evolution and Integrated Risk Assessment of Potentially Toxic Element Pollution in Coastal Waters: A Case Study of Bohai Bay Cases in China

Under the increasing pressures of land-based pollution and intensive coastal development, marine ecosystems are facing unprecedented challenges, highlighting the urgent need for enhanced protection and management of marine environmental quality. This study examines the spatiotemporal distribution and pollution risks of seven potentially toxic elements (Hg, Cd, Pb, Cr, As, Zn, and Cu) in the coastal waters of Bohai Bay, China, based on monitoring data collected from 2020 to 2023. Results show a significant decline in annual average concentrations of Pb (from 3.23 ± 1.11 μg/L to 0.10 ± 0.06 μg/L) and Hg (from 0.05 ± 0.02 μg/L to 0.01 ± 0.00 μg/L), reflecting effective pollution control measures. In contrast, Cu concentrations nearly doubled, rising from 0.90 ± 0.50 μg/L in 2020 to 1.98 ± 0.42 μg/L in 2023, while Zn exhibited a "V"-shaped fluctuation over the study period. Spatially, Zn, Pb, and Hg displayed pronounced clustering patterns, with coefficients of variation (CV) of 1.04, 1.49, and 1.17, respectively. The Pollution Load Index (PLI) decreased from 1.82 in 2020 to 0.94 in 2023, indicating an overall improvement in ecological quality. However, the Risk Index (RI) reached a maximum of 672.5 at Site 11 in 2020, with Hg and Cd contributing 49.6% and 22.7% to the total risk, respectively. Health risk assessment revealed non-carcinogenic risks (Hi) below the safety threshold (Hi < 1) across all sites. In contrast, carcinogenic risks (CR) ranged from 5.7 × 10^-4 to 9.1 × 10^-4, approaching the acceptable upper limit of 10^-3, primarily due to dermal exposure to Hg and the high toxicity of Cd. Principal Component Analysis (PCA) suggested familiar sources for Hg, Pb, and Zn, whereas As appeared to originate from distinct pathways. Overall, this study establishes an integrated "pollution-ecological-health" assessment framework, offering scientific support for targeted pollution prevention and zonal management strategies in coastal environments.