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

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 (delta Hg-202) were observed in the ECS, with delta Hg-202 ranging from -1.86 to -0.83 parts per thousand and Delta Hg-199 ranging from -0.07 to +0.26 parts per thousand. The high delta Hg-202 values and relatively negative Delta Hg-199 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 delta Hg-202 and positive Delta Hg-199, 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 delta Zn-66 ranging from 0.20 to 0.67 parts per thousand. The results showed significant variations of delta Zn-66 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. (C) 2018 Elsevier Ltd. All rights reserved.