Fractionation behaviors of Cu, Zn, and S-O isotopes in groundwater contaminated with petroleum and treated by oxidation

초록

Fractionation behaviors of Cu and Zn isotopes have been increasingly studied at the field scale, but those in various redox conditions of groundwater contaminated with petroleum and treated by oxidation have not been assessed. In this study, 865Cu and 866Zn as well as 834SSO4 and & UDelta;818OSO4-H2O were assessed in wells undergoing contamination by total petroleum hydrocarbons (TPH) and oxidation using H2O2 in 2021 and 2022. High 834SSO4 and relevant parameters (e.g., dissolved sulfide and HCO3- ) indicated the occurrence of sulfate reduction. The plot of 865Cu versus 834SSO4 effectively indicated precipitation of Cu sulfides and their reoxidation at oxidation wells. Although the plot of 866Zn versus 834SSO4 could also indicate reoxidation of Zn sulfides, the Zn isotopic fingerprint of sulfide precipitation may have been masked by fractionation by sorption. The advantage of using 865Cu in the redox reactions resulted from the wider range of 865Cu owing to the redox behavior of Cu. The plot combining isotopic fractionations of Cu and S can assist in assessing sulfide precipitation and oxidative treatment in TPH-contaminated groundwater.

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