Stable Carbon Isotope Fractionation of Trichloroethylene Oxidized by Potassium Permanganate Under Different Environmental Conditions
Stable isotope analysis is a powerful tool for inferring and quantifying transformation processes, but its effectiveness relies on understanding the magnitude and variability of isotopic fractionation associated with specific reactions. Potassium permanganate (KMnO<sub>4</sub>) is widely...
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| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-06-01
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| Series: | Applied Sciences |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2076-3417/15/13/7142 |
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| Summary: | Stable isotope analysis is a powerful tool for inferring and quantifying transformation processes, but its effectiveness relies on understanding the magnitude and variability of isotopic fractionation associated with specific reactions. Potassium permanganate (KMnO<sub>4</sub>) is widely used as an efficient oxidant for the degradation of trichloroethylene (TCE); however, the influence of environmental factors on the isotope fractionation during this process remains unclear. In this study, compound-specific isotope analysis (CSIA) was conducted to investigate the variability in carbon isotope effects during the KMnO<sub>4</sub>-mediated degradation of TCE under varying conditions, including initial concentrations of KMnO<sub>4</sub> and TCE, the presence of humic acid (HA), pH levels, and inorganic ions. The results showed that the overall carbon isotope enrichment factors (ε) of TCE ranged from −26.5 ± 0.5‰ to −22.8 ± 0.9‰, indicating relatively small variations across conditions. At low KMnO<sub>4</sub>/TCE molar ratio (n(KMnO<sub>4</sub>)/n(TCE)), incomplete oxidation and/or MnO<sub>2</sub>-mediated oxidation of TCE likely resulted in smaller ε. For dense, non-aqueous phase liquid (DNAPL) TCE, which represents extremely high concentrations, the ε value was −13.0 ± 1.7‰ during KMnO<sub>4</sub> oxidation. This may be attributed to the slow dissolution of isotopically light TCE from the DNAPL phase, altering the δ<sup>13</sup>C signature of the reacted TCE and resulting in a significantly larger ε value than observed for dissolved-phase TCE oxidation. The ε values increased with rising pH, probably due to the decrease in oxidation potential (E<sub>0</sub>) of KMnO<sub>4</sub> from pH ~2 to ~12, as well as the emergence of different degradation pathways and intermediates under varying pH conditions. Both SO<sub>4</sub><sup>2−</sup> and NO<sub>3</sub><sup>−</sup> slightly influenced the ε values, potentially due to the formation of H<sub>2</sub>SO<sub>4</sub> and HNO<sub>3</sub> at lower pH, which may act as auxiliary oxidants and contribute to TCE degradation. A high concentration (50 mM) of HA led to a decrease in ε values, likely due to competitive interactions between HA and TCE for KMnO<sub>4</sub>, which reduced the effective oxidation of TCE. Overall, the carbon isotope enrichment factors for KMnO<sub>4</sub>-mediated TCE degradation are relatively stable, although certain environmental conditions can exert minor influences. These findings highlight the need for caution when applying quantitative assessment based on CSIA for KMnO<sub>4</sub> oxidation of TCE. |
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| ISSN: | 2076-3417 |