Pollution characterization and source apportionment of HCH and DDT in sewage irrigation soil of Xiao Qing River wetland

To investigate the residues and pollution sources of DDT and HCH in the Xiao Qing River sewage irrigated wetland and study the distribution of pollutants (DDT and HCH) along the vertical soil profile, soil samples were pretreated by Soxhlet extraction and silica gel purification, and the HCH and DDT content were analyzed by GC-MS. The results show that the concentrations of ΣHCHs and ΣDDTs in the soils range from ND-0.225 μg/kg and ND-1.204 μg/kg respectively, with the mean concentrations of 0.042 μg/kg and 0.204 μg/kg. The concentrations of DDTs and HCHs are below the national soil environmental quality standards (GB 15618-1995), which are at a low residue levels. The HCH residues in wetlands without irrigation are caused mainly by historical pesticide using and there is few pollutions generated recently. DDT contamination of wetlands exists mainly in the form of DDE, that is due to historical pesticide using. Sewage irrigation reduced soil residues of DDT and HCH, with average reduction rate of 67.16% and 78%. The HCH residues are higher than DDT residues at the same point. The DDT contents drop sharply along the soil profiles, and the HCH contents change irregularly along the soil profiles.