Spatial Distribution of Hexachlorocyclohexanes in Agricultural Soils in Zhejiang Province, China, and Correlations with Elevation and Temperature

Large quantities of hexachlorocyclohexanes (HCHs) were historically applied to soils in Zhejiang, a hilly province of eastern China, yet very limited information is publicly available for the present levels and residue characteristics of HCHs in the region. In this work, concentrations of HCHs and enantiomeric fractions (EFs) of alpha-isomer were analyzed in 58 agricultural soil samples (0-20 cm) collected in Zhejiang province. On the basis of the ratio of alpha-HCH/beta-HCH and the fact that HCHs were banned in 1983 for agricultural use in China, fresh application of technical HCHs in a large quantity was unlikely in this province. Significant correlation was found between soil concentrations and elevation (R = 0.52, P < 0.001) and temperature (R = -0.55, P < 0.0001), but not between soil concentrations and total technical usage (R = -0.24, P = 0.1), suggesting a typical secondary distribution pattern. The soil residue inventories of HCHs derived from the relationship between concentration and elevation indicated 14.2 tons of HCHs left in agricultural soils in plain areas with the average elevation less than 100 m, and 61.6 tons of HCHs left in mountain soils with the average elevation higher than 100 m. It was also found that EFs of alpha-HCH were significantly negatively correlated with carbon biomass (C-bio) in soils. This implies that C-bio might have important impact on orientation and extent of enantioselective degradation of alpha-HCH in the region, which is, according to our knowledge, the first report of this kind.