Vertical Migration Characteristics of Organochlorine Pesticides in Overlying Soil in Karst Terranes and Its Impact on Groundwater

Five soil profiles and four typical epikarst springs were selected in Nanchuan District, Chongqing Municipality as objects of the study on vertical migration of organochlorine pesticides (OCPs) in the soils and its impact on groundwater. OCPs in soil and epikarst spring water samples were quantitatively analyzed by gas chromatography. The results showed that HCHs and DDTs were detected in all the 5 soil profiles, varying in the range of 0.77-18.3 and 0.34-226 ng · g(-1), and averaging 5.16 and 16 ng · g(-1) in concentration, respectively. The highest concentrations of HCHs and DDTs were found in the subsoil (10-40 cm) in most sampling sites. The detection ratios of HCHs and DDTs in four springs were 100%. The concentrations of HCHs and DDTs fluctuated greatly in epikarst spring water during the one-year observation, and the concentration ranged from 2.09 to 60.1 and from N. D. to 79.8 ng · L(-1), with a mean value of 12 and 9.16 ng · L(-1), respectively. The concentrations of HCHs and DDTs in Hougou, Baishuwan and Lanhuagou spring in rainy season were all. higher than those in dry season in these three epikarst springs. There were no good corresponding relationship between HCHs and DDTs contents in spring water and those in corresponding spring catchment soil. TOC, soil water content, clay content and pH all inhibited the vertical migration of OCPs in Hougou spring catchment, which led to the lowest content of OCPs in spring water, although the OCPs content in Hougou spring catchment soils was the highest in the four spring catchments. However, the four factors didn't inhibit the vertical migration of OCPs in Shuifang spring catchment, which led to higher OCPs content in spring water, although the OCPs content in spring catchment soils was the lowest in the four spring catchments.