Environmental forensics approach to source investigation in a mercury contaminated river: Insights from mercury stable isotopes

Impacts of dam construction on mercury methylation and bioaccumulation revealed by stable isotopes

Impacts of dam construction on mercury (Hg) sources, biogeochemical cycling, and bioaccumulation were investigated along the west coast of Korea, where large-scale national projects were initiated between 1978 and 1990 to build dam or weir at the interface between rivers and estuaries. Total Hg (THg) and methylmercury (MeHg) concentrations and Hg stable isotopes in estuarine sediment cores sampled downstream of dam/weir reveal 74 ± 3% reduction in THg, 536 ± 158% increase in MeHg, and shifts in Hg sources from riverine export to wet deposition (precipitation) as revealed by increases in Δ199Hg (by 0.13 ± 0.03‰) and Δ200Hg (by 0.10 ± 0.01‰). Stable carbon isotopes, n-alkanes, and four geochemical pools of Hg extracted from the sediment cores show enhanced proportion of labile (F1; 0.28 ± 0.21% points) and organically-bound (F2; 34 ± 12% points) Hg fractions and the ratio of marine-based organic matter relative to recalcitrant Hg bound to terrestrial organic matter at the downstream estuary. Dam/weir constructions have significant effects on Hg bioavailability and methylation, by enhancing the proportion of dissolved Hg delivered by precipitation and those subject to efficient assimilation by marine algae and microbial utilization. This is evident by the negative δ202Hg shifts in the sediment cores at the depths of MeHg peaks. Cessation of riverine Hg input is manifested by 96% reduction of THg in shellfish and enhanced methylation appears to cause 106% increase in fish THg at the downstream estuarine ecosystem. This study underscores the importance of considering complex and long-term biogeochemical modifications as a part of Environmental Impact Assessments.

Effects of hydrologic regimes on the loading and spatiotemporal variation of mercury in the microtidal river estuary

The potential effect of hydrological conditions on distribution and loadings of Hg species was investigated in the microtidal Hyeongsan River Estuary (HRE). Dissolved Hg (DHg) and dissolved methylmercury (DMeHg) from the creek receiving industrial wastes were effectively settled to sediment during the post-typhoon period, while persistent input from the Hg-contaminated creek without settling was observed during the dry periods. The event-based mean approach was applied to explore the hydrological effects on the annual flux of Hg. The largest inputs of DHg and particulate Hg (PHg) were found in the Hg-contaminated creek, and DHg input was higher in the dry than wet periods whereas PHg input was higher in the wet than dry periods. In sediment, Hg and MeHg concentrations decreased after the typhoon, attributed to erosion of surface sediments. Overall, the HRE serves as an effective sink of Hg that reduces the degree of Hg contamination in coastal water.

Comprehensive insight into mercury contamination in atmospheric, terrestrial and aquatic ecosystems surrounding a typical antimony-coal mining district

This study comprehensively investigated mercury (Hg) contents of various environmental compartments in a typical antimony-coal mining area with intensive industrial activities over the past 120 years to analyze Hg environmental behaviors and evaluate Hg risks. The total mercury (THg) contents in river water, sediments, soils, PM10, dust falls, vegetables and corns were 1.16 ± 0.63 µg/L, 2.01 ± 1.64 mg/kg, 1.87 ± 3.88 mg/kg, 7.87 ± 18.68 ng/m3, 13.01 ± 14.53 mg/kg, 0.30 ± 0.34 mg/kg and 3.11 ± 0.51 µg/kg, respectively. The δ202Hg values in soils and dust falls were - 1.58 ∼ 0.12‰ and 0.25 ∼ 0.30‰, respectively. Environmental samples affected by industrial activities in the Xikuangshan (XKS) presented higher THg and δ202Hg values. Binary mixing model proved that atmospheric deposition with considerable Hg deposition flux (0.44 ∼ 6.40, 3.12 ± 2.20 mg/m2/y) in the XKS significantly contributed to Hg accumulations on surface soils. Compared with soils, sediments with more frequent paths and higher burst probabilities presented higher dynamic Hg risks. Children were faced higher health risk of multiple Hg exposure than adults. Furthermore, the health risk of THg by consuming leaf vegetables deserved more attention. These findings provided scientific basis for managing Hg contamination.