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The Xikuangshan (XKS) mine in central China is the largest antimony (Sb) mine in the world. The mining activity has seriously contaminated the waters in the area. To determine the sources, migration and transformation of Sb contamination, 32 samples from groundwater (aquifer water), surface water and mine water were collected for water chemistry, trace element and SSO4 and Sr stable isotope analyses. The results showed that the groundwater and surface water were in an oxidized environment. The SSO4 and Sr isotope compositions in the water indicated that dissolved Sb and SO4(2) originated from sulfide mineral (Sb2S3) oxidation, whereas radiogenic Sr may have been sourced from silicified limestone and stibnite in the Shetianqiao aquifer. Furthermore, a positive correlation between δ(34)SSO4 and δ(87)Sr values revealed that the Sr, S and Sb in the waters had a common contamination source, i.e., silicified limestone and stibnite, whereas the Sr, S and Sb in rock and ore were sourced from Proterozoic basement clastics. The analysis also indicated that the isotope composition of dissolved SO4(2-) had been influenced by slight bacterial SO4 reduction in the Magunao aquifer. Mining or rock collapse may have caused Shetianqiao aquifer water to contaminate the Magunao aquifer water via mixing. This study has demonstrated that the stable isotopes of (34)SSO4 and (87)Sr, combined with hydrochemical methods, are effective in tracking the sources, migration and transformation of Sb contamination., (Copyright © 2016 Elsevier B.V. All rights reserved.)

We describe a method to determine the nitrogen and oxygen isotopic composition of nitrate in groundwater samples ((15)N/(14)N and (18)O/(16)O, respectively), which is based on the analysis of nitrous oxide gas (N2O) that is produced quantitatively from nitrate by denitrifying bacteria. This method which is simple, inexpensive and effective in the removal of nitrite is greatly selective for NO2(-) and was used for mixed samples containing both NO2(-) and NO3(-) with little or no measurable cross-contamination. The precision of δ(15)N and δ(18)O are 0.3 and 0.17‰ respectively, compared to that of 0.1 and 0.5‰ abroad (Brand et al. in Org Geochem 21:585-594, 1994; Begley and Scrimgeour in Anal Chem 69(8): 1530-1535, 1997; Kornexl et al. in Rapid Commun Mass Spectrom 13(16):1685-1693, 1999; Böhlke et al. in Rapid Commun Mass Spectrom 17:1835-1846, 2003; Gehre and Strauch in Rapid Commun Mass Spectrom 17(13):1497-1503, 2003; Werner in Isot Environ Health Stud 39:85-104, 2003).

The Xikuangshan(XKS) mine, the world’s largest antimony mine, was chosen for a detailed arsenic hydrogeochemical study because of the elevated arsenic in bedrock aquifers used by local residents. Hydrochemical data, δ 34 S values of dissolved SO 4 2− and 87 Sr/ 86 Sr ratios have been analyzed to identify the predominant geochemical processes that control the arsenic mobilization within the aquifers. Groundwater samples can be divided into three major types: low arsenic groundwater (0–50 µg/L), high arsenic groundwater (50–1000 µg/L) and anomalous high arsenic groundwater (>1000 µg/L). Arsenic occurs under oxidizing conditions at the XKS Sb mine as the HAsO 4 2− anion. The Ca/Na ratio correlates significantly with HCO 3 − /Na and Sr/Na ratios, indicating that carbonate dissolution and silicate weathering are the dominant processes controlling groundwater hydrochemistry. The δ 34 S values of the groundwater indicate that dissolved SO 4 2− in groundwater is mainly sourced from the oxidation of sulfide minerals, and elevated As concentrations in groundwater are influenced by the mixing of mine water and surface water. Furthermore, the δ 34 S values are not correlated with dissolved As concentrations and Fe concentrations, suggesting that the reduction dissolution of Fe(III) hydroxides is not the dominant process controlling As mobilization. The 87 Sr/ 86 Sr ratios imply that elevated As concentrations in groundwater are primarily derived from the interaction with the stibnite and silicified limestone. More specifically, the excess-Na ion, the feature of Ca/Na ratio, and the spatial association of elevated As concentrations in groundwater collectively suggest that high and anomalous high arsenic groundwater are associated with smelting slags and, in particular, the arsenic alkali residue. In general, the hydrochemistry analysis, especially the S and Sr isotope evidences elucidate that elevated As concentrations and As mobilization are influenced by several geochemical processes, including: (1) bedrock weathering; (2) oxidation of arsenopyrite and the dominant sulfides in the ores; (3) mixing of mine drainage and surface water; (4) leaching of the arsenic alkali residue; and (5) sorption-desorption from Fe/Mn oxides/hydroxides. [ABSTRACT FROM AUTHOR]

In the south coast of Laizhou Bay, due to intensive groundwater extraction since the 1970s, salt water intrusion has occurred seriously, which increased the stress on regional fresh water resources. It is of great importance to understand origin of salinity and salinization process in coastal aquifers. To trace source and transport of dissolved bromide as a perfect representative of salinity and reveal genesis of salinized groundwater in regional aquifer system, Br stable isotopes of the sampled waters were surveyed coupled with hydrochemistry and stable H/O isotopes along the direction from inland to shore. The results show that groundwater salinity, hydrochemistry and stable isotopes exhibit regular variation from inland to shore. The TDS values of the groundwater increase gradually ranging from 0.52 to 133.74 g/L, the chemical types transform from Cl–Ca and HCO 3 –Ca to Cl–Na, 2 H and 18 O are getting more and more enriched, and the δ 81 Br values decrease gradually, from inland to shore. Trends of major ions versus bromide and Br isotope signatures for brine indicate brine originated from seawater evaporation followed by some water–rock interaction processes. The hydrogen and oxygen isotope signatures of the brine indicate the dilution by fresh water of meteoric origin was a probable process during or after brine formation. The δ 81 Br values of brine samples show good anticorrelation to both δ 2 H and δ 18 O values, probably confirming the addition of fresh water. The potential contribution of evaporate dissolution as a primary process to the brine was ruled out based on their Br isotope signatures. Trends of major ions versus bromide and H/O stable isotopes for brackish water reveal brine intrusion has occurred and mixed with fresh water inland, and Br stable isotopic composition of brackish water indicates that marine aerosol input could enrich the dissolved bromide in brackish water except for brine intrusion. Other processes, such as diffusion, subaerial evaporation and anthropogenic activities may change the budget of dissolved Br − , but are not primary processes responsible for behavior of Br stable isotope in shallow brackish water. Major contribution of meteoric water in deep fresh water and more influence by brine in deep saline water were revealed based on the Br isotopic results. [ABSTRACT FROM AUTHOR]