Mercury Sources and Processes Implied by Other Pollutants Distributions in Surface Water and Sediments of a Subtropical Estuary in Southern China

Concentrations and isotopic compositions of mercury in surface water and surface sediment of the Jiulong River Estuary (JRE) were measured. Differences in total mercury (THg) concentrations in surface water between dry and wet seasons were insignificant, which was also the case with surface sediment THg levels. Large variations in Hg isotopic compositions were observed both in surface water (δ 202 Hg: − 1.53 to 0.61‰; Δ 199 Hg: − 0.22 to 0.20‰) and surface sediment (δ 202 Hg: − 2.64 to − 0.96‰; Δ 199 Hg: − 0.27 to 0.25‰). Concentration correlations between mercury and dissolved inorganic nitrogen (DIN) implied that mercury in surface sediment may undergo resuspension and be re-emitted to the water surface. The negative Δ 199 Hg in most of the surface sediments and the correlation between mercury and DIN in the wet season indicate that soil erosion is the major source of mercury. The main sources of mercury in surface water are precipitation and natural soil. The correlation between mercury and dissolved inorganic carbon, perfluoroalkyl substances, polycyclic aromatic hydrocarbons, and dissolved Cd indicates that the contribution of underground water and industrial and urban waste cannot be ignored, which is supported by the positive signature of Δ 199 Hg. The results of the isotopic analysis also indicate that atmospheric dry deposition is another source of mercury in surface water. The study suggests that the mercury distribution in the estuary is related to some other pollutants. Both using mercury isotope signatures and the distribution links between mercury and other pollutants can be used to better understand the processes and sources of mercury in the estuary.