Compound Specific and Enantioselective Stable Isotope Analysis as Tools To Monitor Transformation of Hexachlorocyclohexane (HCH) in a Complex Aquifer System

Abstract

Technical hexachlorocyclohexane (HCH) mixtures and Lindane (γ-HCH) have been produced in Bitterfeld-Wolfen, Germany, for about 30 years until 1982. In the vicinity of the former dump sites and production facilities, large plumes of HCHs persist within two aquifer systems. We studied the natural attenuation of HCH in these groundwater systems through a combination of enantiomeric and carbon isotope fractionation to characterize the degradation of α-HCH in the areas downstream of a former disposal and production site in Bitterfeld-Wolfen. The concentration and isotope composition of α-HCH from the Quaternary and Tertiary aquifers were analyzed. The carbon isotope compositions were compared to the source signal of waste deposits for the dumpsite and highly contaminated areas. The average value of δC at dumpsite was -29.7 ± 0.3 ‰ and -29.0 ± 0.1 ‰ for (-) and (+)α-HCH, respectively, while those for the β-, γ-, δ-HCH isomers were -29.0 ± 0.3 ‰, -29.5 ± 0.4 ‰, and -28.2 ± 0.2 ‰, respectively. In the plume, the enantiomer fraction shifted up to 0.35, from 0.50 at source area to 0.15 (well T1), and was found accompanied by a carbon isotope enrichment of 5 ‰ and 2.9 ‰ for (-) and (+)α-HCH, respectively. The established model for interpreting isotope and enantiomer fractionation patterns showed potential for analyzing the degradation process at a field site with a complex history with respect to contamination and fluctuating geochemical conditions.

Compound-Specific Isotope Analysis and Enantiomer Fractionation to Characterize the Transformation of Hexachlorocyclohexane Isomers in a Soil–Wheat Pot System

“…could be applied to characterize the aerobic α-HCH degradation. , Enantiomer fraction (EF) is an indicator of the biotransformation of chiral compounds and can indicate the selective uptake processes of specific enantiomers . Several studies have combined the CSIA and EF to characterize the microbial transformation of α-HCH at the laboratory scale and in aquifers at the landscape level. , The application of CSIA and EF methods in the soil–plant system could give impetus for characterizing the fate of organic pollutants in complex systems, and it is a huge step toward the development of the methods.…”

“…19 Several studies have combined the CSIA and EF to characterize the microbial transformation of α-HCH at the laboratory scale and in aquifers at the landscape level. 17,20 The application of CSIA and EF methods in the soil−plant system could give impetus for characterizing the fate of organic pollutants in complex systems, and it is a huge step toward the development of the methods. Wu et al 21 analyzed the isotope composition of HCHs in plants and soil to monitor the transformation of HCHs at a contaminated field site.…”

Solid-phase extraction method for stable isotope analysis of pesticides from large volume environmental water samples

“…16 Various analytical methods have been recently developed. [17][18][19][20][21][22][23][24][25][26][27][28][29] Nonetheless, application of CSIA of pesticides to field studies remain scarce 24,[30][31][32][33][34] because of two major challenges. First, isotope effect-free extraction and pre-concentration methods are required to allow CSIA at low environmentally relevant concentrations by gas chromatography-isotope ratio mass spectrometry (GC/IRMS) or -in the case of compounds like desphenylchloridazon for which GC/IRMS-based carbon isotope analysis does not work -by liquid chromatography-IRMS (LC/IRMS).…”

Can Alkaline Hydrolysis of γ-HCH Serve as a Model Reaction to Study Its Aerobic Enzymatic Dehydrochlorination by LinA?

“…According to estimates 1.7–4.8 million tons of HCH are still present widely in nature [6]. Isotope fractionation concepts have been used to elucidate transformation reactions of HCH in field studies [7,8] and diagnostically to characterize transformation reactions even in food webs [9,10].…”