Spatial distributions and sources of heavy metals in sediments of the Changjiang Estuary and its adjacent coastal areas based on mercury, lead and strontium isotopic compositions

Abstract

The distribution, source and fate of the heavy metals mercury (Hg) and lead (Pb) in surface sediments from the East China Sea (ECS) were studied using mercury, lead and strontium (Sr) isotopic ratios. Hydrodynamic circulation and the sedimentary depositional process within the ECS were the dominant factors controlling the distribution and fate of heavy metals, referring from relationships of heavy metals (Hg and Pb) concentrations and total organic carbon (TOC) and clay contents. Spatial variations in Hg isotopic compositions (δ202Hg) were observed in the ECS, with δ202Hg ranging from −1.86 to −0.83‰ and Δ199Hg ranging from −0.07 to +0.26‰. The high δ202Hg values and relatively negative Δ199Hg values in estuarine and inner shelf sites indicated that the riverine inputs from Changjiang River played an important role in delivering Hg to ECS. In contrast, Hg isotopic signatures in outer shelf sediments had relatively low δ202Hg and positive Δ199Hg, implying that atmospheric Hg deposition could be a relatively dominant source for Hg. Using these Hg isotope compositions, the source attributions of sediments in ECS were estimated based on a triple mixing model, suggesting that river-dominated inputs, discharging pollutants from industrial sources, and atmospheric deposition could dominate in the occurrence and fate of Hg in surface sediments of ECS. Moreover, the results of Pb and Sr isotopic ratios in surface sediment samples and potential sources showed that the Pb accumulated in the ECS was mainly from background and anthropogenic sources, with the contribution rates of 45% and 55%, respectively.