Spatial redistribution and enantiomeric signatures of hexachlorocyclohexanes in Chinese forest soils: Implications to environmental behavior and influencing factors.

Hexachlorocyclohexanes (HCHs) are a group of highly persistent pesticides. The concentrations of HCHs and the enantiomeric fractions of α-HCH in the O- and A-horizons from 30 mountains across China were analyzed in this study. The concentrations of total HCHs ranged from 0.061 to 46.9 ng/g (mean 2.12 ng/g) and 0.046 to 16.1 ng/g (mean 0.792 ng/g) in the O- and A-horizons, respectively. The HCH residues were mainly derived from the historical applications of technical HCH and lindane. Higher concentrations of HCHs were typically found in northern China, and no significant correlations were found between historical technical HCH usage and HCH isomer concentrations in either the O- or A-horizons (p > 0.05). Conversely, the concentrations of HCH isomers were significantly correlated with the environmental parameters (temperature and precipitation), thus indicating a typical secondary distribution pattern. Some HCH isomers tended to be transported northward under the long-term effect of monsoon. Chiral α-HCH was non-racemic in soils and showed preferential degradation of (-) α-HCH in both the O- and A-horizons. The transformation from γ-HCH to α-HCH might alter the enantiomeric signatures of α-HCH in soils. Moreover, the deviation from racemic of α-HCH was positively correlated with the C/N ratio in the A-horizon (p < 0.01), thus suggesting that the C/N ratio could alter the microbial activity and significantly affect the enantioselective degradation extent of α-HCH in soils.