Compound-Specific Stable Isotope Analysis: Implications in Hexachlorocyclohexane in-vitro and Field Assessment

Abstract

Assessment of biotic and abiotic degradation reactions by studying the variation in stable isotopic compositions of organic contaminants in contaminated soil and aquifers is being increasingly considered during the last two decades with development of Compound specific stable isotope analysis (CSIA) technique. CSIA has been recognized as a potential tool for evaluating both qualitative and quantitative degradation with measurement of shifts in isotope ratios of contaminants and their degradation products as its basis. Amongst a wide variety of environmental pollutants including monoaromatics, chlorinated ethenes and benzenes etc., it is only recently that its efficacy is being tested for assessing biodegradation of a noxious pollutant namely hexachlorocyclohexane (HCH), by pure microbial cultures as well as directly at the field site. Anticipating the increase in demand of this technique for monitoring the microbial degradation along with natural attenuation, this review highlights the basic problems associated with HCH contamination emphasizing the applicability of emerging CSIA technique to absolve the major bottlenecks in assessment of HCH. To this end, the review also provides a brief overview of this technique with summarizing the recent revelations put forward by both in vitro and in situ studies by CSIA in monitoring HCH biodegradation.

Keywords: Biodegradation; Contaminant; Fractionantion; Hexachlorocyclohexane; Isotopes.

Fig. 1

Schematic representation of the common Gas Chromatography (GC) interface for carbon isotope measurements (as CO₂) with a basic layout of an Isotope ratio mass spectrometer (IRMS)

Fig. 2

Bar graph representing the comparative profile of enrichment factors observed from the anaerobic, aerobic and chemical degradation of bulk α-HCH,(+)/(−) α-HCH enantiomers and γ-HCH as per the data represented in Badea et al. 2011, Badea et al. 2009, Bashir et al. 2013, Zhang et al. 2014, Supplementary Table SI