Implications of seawater characteristics on dissolved heavy metals in near-shore surface waters of the Yellow Sea.

Abstract

To explore the response of dissolved heavy metals (HMs) along the Yellow Sea coast to seawater characteristics, we assessed the temporal and spatial variations as well as pollution levels of six dissolved HMs (Cu, Zn, Pb, Cd, Hg, and As) in surface seawater from 2021 to 2023. The results indicated that the average concentrations of HMs in the seawater were ranked as follows: Zn > Cu > As > Pb > Cd > Hg, with specific concentration ranges of 4.70-7.01, 0.64-2.83, 0.02-2.83, 0.05-1.37, 0.14-0.55, and 0.02-0.20 μg L^-1, respectively. Spatial distribution revealed irregular fluctuations in HM concentrations between nearshore and offshore regions. Analyses of the metal sources suggested that HMs were diffusing from nearshore to offshore, indicating that land-based inputs were the primary source of dissolved HMs along the coast of the Yellow Sea. During the study period, Hg exceeded environmental safety threshold in the study area, indicating a potential ecological risk from Hg pollution. Furthermore, Pb showed signs of pollution in certain seasons. Regarding the correlation of variables, Cu showed the strongest correlation with temperature and dissolved oxygen (DO), but Zn showed a significant correlation with temperature and salinity. Differently, Pb, Cd, Hg, and As were markedly associated with DO and salinity. The complex interactions between environmental variables significantly influenced HM concentrations, and no single factor could adequately explain these changes. Taken together, the alterations in seawater characteristics along the coast of the Yellow Sea had significantly impacted the dissolved HMs during the study period.