Spatial and seasonal variations in air-soil exchange, enantiomeric signatures and associated health risks of hexachlorocyclohexanes (HCHs) in a megacity Hangzhou in the Yangtze River Delta region, China.

Large amounts of hexachlorocyclohexanes (HCHs) have been historically applied in the Yangtze River Delta (YRD) region, China. Estimating the air-soil exchange of HCHs after >30years of restricted use is important for understanding their cycling in the environment. In this study, air and soil samples were concurrently collected in two seasons at agricultural and industrial sites from a megacity in the YRD region. The concentrations of HCH isomers and the enantiomeric fractions of chiral α-HCH were determined. The mean concentrations of ∑HCHs in soils from an agricultural area (AA) and an eco-industrial park (EIP) were 1.74ng/g and 0.652ng/g, respectively, in winter, and 0.723ng/g and 0.350ng/g, respectively, in summer. The mean concentrations of ∑HCHs in the air from the AA and the EIP were 31.2pg/m and 47.7pg/m, respectively, in winter, and 45.0pg/m and 50.0pg/m, respectively, in summer. The variations in spatial and seasonal distributions might be related to diverse geographical factors, soil properties and meteorological conditions. Source identification demonstrated that HCHs in most samples were residues from past use, which was further evidenced by the enantiomeric signatures of chiral α-HCH. A preferential degradation of (-)-α-HCH was showed in soils and summer air, while a preferential depletion of (+)-α-HCH was displayed in winter air. The values of the fugacity fraction (ff) of HCHs suggest a net volatilization from soils to air, but long-range transport may also partly contribute to the atmospheric HCHs according to the results from enantiomeric analysis. The human health risk assessments indicated an absence of noncarcinogenic risks and very low carcinogenic risks for HCHs in both soils and air to human health. Results from this study provide valuable data for assessing the fate and health risks of HCHs in the YRD region.