CARBON ISOTOPE EFFECT DURING THE ABIOTIC OXIDATION OF METHYL-TERT-BUTYL ETHER (MTBE)

摘要

Compound specific isotope analysis (CSIA) is increasingly being used to determine degradation rates and pathways for organic contaminants. Here we compare carbon isotope effects associated with published biotic reactions with new results from the abiotic oxidation of MTBE to better understand the role of both in the fate of MTBE in the environment. The study focused on abiotic oxidation and isotopic fractionation associated with the reaction of potassium permanganate (KMnO4) with MTBE. At >95 % completion of the reaction a significant shift in δ13C of was observed due to the preferential oxidation of the lighter isotope. The isotopic enrichment fraction (ε) was calculated to be between - 4.2‰ and -4.9‰ which when compared to enrichments reported in literature for biotic reactions (-1.5‰ to -2.4‰) shows a significant variation which could allow for the differentiation of reaction mechanisms. Gasoline samples where collected worldwide to look at the possible range of δ13C for MTBE for different blends and to establish whether the fractionation associated with degradation would be outside this range. The samples where found to have a δ13C range between -27.4‰ and -32.0‰ (± 0.4‰). The study also looked at the difference in δ13C when analysing MTBE in organic and gaseous phases. A small enrichment in 13C was observed in the organic phase but is not significant enough to have an effect on comparisons.