RATIONALE: The manufacturing and uses of hexachlorocyclohexane (HCH) have resulted in a serious environmentalchallenge and legacy. This study highlights the ability of compound specific isotope analysis (CSIA) to distinguishamong various HCH sources and to support the evaluation of the potential for in situ biodegradation in contaminatedgroundwater.
METHODS: Tests were conducted to verify the absence of significant isotope fractionation during HCH sample preconcentrationincluding dichloromethane extraction, solvent exchange into iso-octane, and H2SO4 clean-up, and analysisby gas chromatography/combustion-isotope ratio mass spectrometry (GC/C-IRMS). The method was then applied tofour Technical Grade (TG) HCH mixtures procured from different sources and to groundwater samples from acontaminated site.
RESULTS: The pre-concentration method enabled determination of carbon isotope ratios (δ13C values) of HCH isomerswith no significant isotopic fractionation. The TG-HCH mixtures had significantly different δ13C values. Moreover, forany given TG-HCH, all isomers had δ13C values within 1.1‰ of each other – a distinctly uniform fingerprint. At theHCH-contaminated field site, compared with source wells, downgradient wells showed significant (up to 5.1‰)enrichment in 13C and the δ13C values of the HCH isomers were significantly different from each other.
CONCLUSIONS: A method was successfully developed for the CSIA of HCH isomers that showed potential for HCHsource differentiation and identification of HCH in situ biodegradation. At the HCH-contaminated site, the observedpreferential isotopic enrichment of certain isomers relative to others for a given source allows differentiation betweenbiodegraded and non-biodegraded HCH.
John Wiley & Sons, 2015. Vol. 29, no 6, 505-514 p.