Historical records, distributions and sources of mercury and zinc in sediments of East China sea: Implication from stable isotopic compositions

Abstract

The distribution and source of mercury (Hg) and zinc (Zn) in surface sediments from East China Sea (ECS) were studied using stable isotopes. Hg concentrations in surface sediments varied from 12.6 to 133.2 ng g−1. Zn concentrations ranged between 45.9 and 133.6 ng g−1. Hydrodynamic circulation and sedimentary process within the ECS were the dominant factors controlling the distribution and fate of heavy metals, referring from relationships of Hg and Zn 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 Yangtze 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 relatively dominant source for Hg. Moreover, application of zinc isotopes to trace anthropogenic sources has been tested, with δ66Zn ranging from 0.20 to 0.67‰. The results showed significant variations of δ66Zn in the ECS, implying that Zn isotope compositions can be tracers of anthropogenic sources. Using these Hg isotope compositions, the source attributions of sediments in ECS were estimated based on a 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 sediments of ECS.