| Organochlorine pesticide (OCP) residues in soils are primary among environmental pollutants and are receiving increasing national and international attention because of the threat they pose to environmental and human health. In this study, we analyzed the distribution and characteristics of OCP residues in the soil of farmland in the Jiulong River watershed, focusing on their level, composition and vertical distribution. The study was based on soil monitoring of OCPs from 2014 to 2016 at 20 sampling sites representing different soil types and land use. Soil samples were collected at different depths (0-10, 10-20, 20-30 cm), and extracted using accelerated solvent extraction (ASE) and determined by gas chromatography. Hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene (HCB) made up 99.40% of the total OCP residues, with HCHs accounting for 56.01%. Chlordane (TC+CC), (TN+CN) and endosulfan (α-End+β-End) residues were low and pose little threat to the farmland soil in the Jiulong River watershed. The OCP levels were concentrated in the surface layer (0-10 cm) and decreased dramatically with soil depth, displaying obvious surface accumulation. The OCP level in the same layer of soil in order of land use was paddy > orchard > vegetable. The average level of DDT isomers was in the order o,p'-DDT > p,p'-DDT > p,p'-DDD and dominated by o,p'-DDT. The average level of HCH residuals was in the order β-HCH > α-HCH > γ-HCH > δ-HCH and the levels of β-HCH and α-HCH are potentially harmful. Principle component analysis revealed that α-HCH, β-HCH, γ-HCH and δ-HCH had highest loading in the first principal component, DDTs the highest loading in the second principal component and TC and CC, α-End and β-End, TN and CN the highest loading in the third principal component. Pearson correlation analysis shows that TOC had an important effect on the level and distribution of OCPs in the soil of farmland in the Jiulong River watershed and the correlation of OCPs, HCHs and HCB with TOC was highly significant (P<0.01). HCHs had a similar distribution and input source with HCB and DDTs, while HCB, DDTs and TN+CN were important determinants of OCP content and distribution. |
