Microbial degradation is a key elimination pathway of hexachlorocyclohexanes from the Arctic Ocean

Geophysical Research Letters 04/2000; 27(8). DOI: 10.1029/1999GL011326

ABSTRACT Hexachlorocyclohexanes (HCHs) are the most abundant pesticides in arctic air and water. We have calculated in situ microbial degradation rates of α- and γ-HCH for the Arctic Ocean using enantiomer ratio (ER) data and concentrations in water at the surface and after it has subducted to depth. The ERs of α-HCH, which provide the first direct evidence of microbial degradation, allow rates to be estimated. The half-lives due to microbial activity for (+)-α-HCH, (−)-α-HCH and γ-HCH (respectively 5.9 ± 1.2, 22.8 ± 4.7 and 18.8 ± 10.1 years) are 3–10 times faster than removal by the only other known breakdown mechanism, hydrolysis (Harner et al., 1999). Microbial degradation is highlighted as an important elimination process in a revised HCH loss budget for the Arctic Ocean, removing 204 t y−1, α-HCH and 23 t y−1, γ-HCH. These tonnages represent 29–37% of the annual HCH removal from the Arctic Ocean.

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    ABSTRACT: Carbon isotope fractionation was investigated for the biotransformation of γ- and α- hexachlorocyclohexanes (HCH) as well as enantiomers of α-HCH using two aerobic bacterial strains: Sphingobium indicum strain B90A and Sphingobium japonicum strain UT26. Carbon isotope enrichment factors (εc) for γ-HCH (εc = -1.5 ± 0.1 ‰ and -1.7 ± 0.2 ‰) and α-HCH (εc = -1.0 ± 0.2 ‰ and -1.6 ± 0.3 ‰) were similar for both aerobic strains, but lower in comparison with previously reported values for anaerobic γ-HCH degradation. Isotope fractionation of α-HCH enantiomers was higher (+) α-HCH (εc = -2.4 ± 0.8 ‰ and -3.3 ± 0.8 ‰) in comparison to (-) α-HCH (εc = -0.7 ± 0.2 ‰ and -1.0 ± 0.6 ‰). The microbial fractionation between the α-HCH enantiomers was quantified by the Rayleigh equation and enantiomeric fractionation factors (ɛe) for S. indicum strain B90A and S. japonicum strain UT26 were -42.8 ± 15.5 % and -22 ± 5.7 %, respectively. The extent and range of isomer and enantiomeric carbon isotope fractionation of HCHs with Sphingobium spp. suggests that aerobic biodegradation of HCHs can be monitored in situ by compound-specific stable isotope analysis (CSIA) and enantiomer-specific isotope analysis (ESIA). In addition, enantiomeric fractionation has the potential as a complementary approach to CSIA and ESIA for assessing the biodegradation of α-HCH at contaminated field sites.
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