Hydrogen isotopic fractionation of petroleum hydrocarbons during vaporization: implications for assessing artificial and natural remediation of petroleum contamination |
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| Institution: | 1. Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany;2. Institute of Applied Radiation Chemistry, Lodz University of Technology, ?eromskiego 116, 90-924 ?ód?, Poland;3. Department of Chemistry, Leibniz Institute for Tropospheric Research (TROPOS), Permoserstraße 15, 04318 Leipzig, Germany |
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| Abstract: | Compound-specific H isotope analysis has been used to monitor bioremediation of petroleum hydrocarbons. However, the success of this approach requires a full evaluation of the isotopic effects resulting from evaporation, because light petroleum hydrocarbons undergo both biodegradation and evaporation under natural conditions. The authors determined the H isotope fractionation of common volatile petroleum hydrocarbons, including the C10–C14 n-alkanes, MTBE (tert-butyl methyl ether), and BTEX (benzene, toluene, ethylbenzene, p-xylene and o-xylene) during progressive vaporization under simulated experimental conditions. A decrease in δD values for n-alkanes of up to 33.3‰ and up to 44.5‰ for BTEX compounds when 99% of these substances had evaporated was observed. The results also show that H isotope fractionation increases with n-alkane chain length. Such fractionation patterns are interpreted in terms of competition between the decreased intermolecular binding energy in D-enriched species, and the isotope effect due to the mass difference. In contrast to hydrocarbons, methanol and ethanol show H isotopic enrichment during vaporization, indicating that H-bonding, when present in organic molecules, plays a controlling role on the vapor pressure of different isotope species. |
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