Isotopic effects of PCE induced by organohalide-respiring bacteria

Abstract

Reductive dechlorination performed by organohalide-respiring bacteria (OHRB) enables the complete detoxification of certain emerging groundwater pollutants such as perchloroethene (PCE). Environmental samples from a contaminated site incubated in a lab-scale microcosm (MC) study enable documentation of such reductive dechlorination processes. As compound-specific isotope analysis is used to monitor PCE degradation processes, nucleic acid analysis-like 16S-rDNA analysis-can be used to determine the key OHRB that are present. This study applied both methods to laboratory MCs prepared from environmental samples to investigate OHRB-specific isotope enrichment at PCE dechlorination. This method linkage can enhance the understanding of isotope enrichment patterns of distinct OHRB, which further contribute to more accurate evaluation, characterisation and prospection of natural attenuation processes. Results identified three known OHRB genera (Dehalogenimonas, Desulfuromonas, Geobacter) in diverse abundance within MCs. One species of Dehalogenimonas was potentially involved in complete reductive dechlorination of PCE to ethene. Furthermore, the isotopic effects of PCE degradation were clustered and two isotope enrichment factors (ε) (- 11.6‰, - 1.7‰) were obtained. Notably, ε values were independent of degradation rates and kinetics, but did reflect the genera of the dechlorinating OHRB.

Carbon isotope effects in the sorption of chlorinated ethenes on biochar and activated carbon

“…Microbial degradation of CE shows high variability in carbon isotope fractionation, ranging from insignificant isotope differences to fractionation factors (ε) of −18.9 ‰ [ 33 , 69 ]. As a consequence, higher threshold values should be considered or interpreted more conservatively for the identification and evaluation of pollutant-degrading processes due to shifts in the carbon isotope ratio of up to −2.4‰.…”

“…The stable carbon isotope ratio of ETs was determined according to Leitner et al (2017) [ 33 ]. Shortly, liquid samples were concentrated by a purge and trap autosampler, single compounds were separated and measured by gas chromatography coupled to isotope ratio mass spectrometry (purge and trap GC-C/IRMS).…”