Tracking the multiple Hg sources in sediments in a typical river-lake basin by isotope compositions and mixing models

Confounding effects of seasonality and anthropogenic river regulation on suspended particulate matter-driven mercury transport to coastal seas

Riverine mercury (Hg) is mainly transported to coastal areas in suspended particulate matter (SPM)-bound form, posing a potential threat to human health. Water discharge and SPM characteristics in rivers vary naturally with seasonality and can also be arbitrarily disrupted by anthropogenic regulation events, but their effects on Hg transport remain unresolved. Aiming to understand the confounding effects of seasonality and anthropogenic river regulation on Hg and SPM transport, this study selected the highly sediment-laden Yellow River as a representative conduit. Significant variations in SPM concentrations (108 - 7097 mg/L) resulted in fluctuations in total mercury (THg, 3.79 - 111 ng/L) in river water corresponding to seasonality and anthropogenic water/sediment regulation. Principal component analysis and structural equation model revealed that SPM was the essential factor controlling THg and particulate Hg (PHg) in river water. While SPM exhibited equilibrium state in the dry season, a net resuspension during the anthropogenic regulation and net deposition in the wet season demonstrated the impact of SPM dynamics on Hg distribution and transport to coastal regions. Combining water discharge, SPM, and Hg concentrations, a modified model was developed to quantify Hg flux (2256 kg), over 98% of which was in particulate phase.

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.

The composition and differences of antimony isotopic in sediments affected by the world's largest antimony deposit zone

Antimony (Sb) isotopic fingerprinting is a novel technique for stable metal isotope analysis, but the use of this technique is still limited, especially in sediments. In this study, the world's most important Sb mineralization belt (the Xikuangshan mineralization belt) was taken as the research object and the Sb isotopic composition and Sb enrichment characteristics in the sediments of water systems from different Sb mining areas located in the Zijiang River (ZR) Basin were systematically studied. The results showed that the ε123Sb values in the sediments of the ZR and its tributaries, such as those near the Longshan Sb-Au mine, the Xikuangshan Sb mine, and the Zhazixi Sb mine, were 0.50‒3.13 ε, 2.31‒3.99 ε, 3.12‒5.63 ε and 1.14‒2.91 ε, respectively, and there were obvious changes in Sb isotopic composition. Antimony was mainly enriched in the sediments due to anthropogenic sources. Dilution of Sb along the river and adsorption of Sb to Al-Fe oxides in the sediment did not lead to obvious Sb isotopic fractionation in the sediment, indicating that the Sb isotopic signature was conserved during transport along the river. The Sb isotopic signatures measured in mine-affected streams may have differed from those in the original Sb ore, and further investigation of Sb isotopic fingerprints from other possible sources and unknown geochemical processes is needed. This study reveals that the apparent differences in ε123Sb values across regions make Sb isotopic analysis a potentially suitable tool for tracing Sb sources and biogeochemical processes in the environment.