AbstractsBiology & Animal Science

The European environment agency listed around 250,000 contaminated field sites which need to be cleaned due to the hazardous effects they pose on human and ecosystem health. This number is expected to increase over the next years. Similar is the case of hexachlorocyclohexane (HCH) contamination and it is estimated that four to six million tons of various HCH materials have been dumped worldwide, which need an urgent removal from the environment. HCH can undergo degradation by microorganisms indigenous to the soil or groundwater. Therefore natural attenuation (NA), relying on the in situ biodegradation of pollutants is considered as a cost effective remediation strategy. However, it requires accurate monitoring techniques. Carbon stable isotope analysis (CSIA) is a powerful technique to provide information on the extent of degradation. α-HCH as many other organic components appear as a racemic mixture of enantiomers in the environment and enantiomer fraction (EF) can provide information on biodegradation. The combination of enantiomeric fraction (EF), CSIA and the enantiomer selective stable isotope analysis (ESIA) has potential for distinguishing transformation processes of contaminants in situ. To validate the applicability of CSIA for HCH, reaction-specific carbon isotope enrichment factors (εc) were determined in laboratory experiments for HCH isomers during aerobic and anaerobic degradation and compared with relevant abiotic reactions. Bulk enrichment factors determined for aerobic degradation of α- and γ-HCH by two Sphingobium spp. with similar reaction mechanism were similar (εc = −1.0 to −1.6 ‰ for α-HCH and εc = −1.5 to −1.7 ‰ for γ-HCH). Carbon isotope fractionation for aerobic degradation was smaller (εc = −1.0 to −1.6 ‰) as compared to anaerobic biodegradation experiments with Dehalococcoides sp. (εc = −5.5 ± 0.8 ‰) and mixed cultures (εc = −3.1 ± 0.4 ‰). For the first time anaerobic HCH transformation coupled with growth of Dehalococcoides mccartyi strain 195 was reported. Furthermore, isomer and enantiomer selective stable isotope fractionation of α-HCH was analyzed during biotic and abiotic reactions. Enantio-selective transformation and carbon isotope fractionation of α-HCH enantiomers was observed only in biotic reference studies. The extent of carbon isotope fractionation in biotic and abiotic transformation was compared to analyze the mechanism of bond cleavage. The enrichment factors of individual enantiomers εenantiomer allowed calculating an average enrichment factor in all cases which was identical with bulk enrichment factors εbulk showing the validity of the analytical approach. The extent and variability of carbon stable isotope fractionation in all laboratory investigations validate the applicability of CSIA as tool to characterize transformation of HCH in the environment. Furthermore, the ESIA method can help to distinguish biotic and abiotic reactions. The ESIA approach has probably potential for tracing the fate of other chiral contaminants in the environment. The evaluation of CSIA at…