Effect of land use change from paddy to vegetable field on the residues of organochlorine pesticides in soils.

The effect of land use change from paddy to vegetable field on the residues of organochlorine pesticides (OCPs) was investigated. Soil residues of OCPs were analyzed in vegetable fields which had been converted from paddy fields for 0, 5, 10, 15, 20, 30, 50 year in Yixing, China in 2003. The mean concentrations of OCPs followed a sequence of: SigmaDDTs (13.7 microg kg(-1))> SigmaHCHs (8.6 microg kg(-1)) >>HCB (2.09 microg kg(-1))>alpha-endosulfan (1.30 microg kg(-1))>endrin (1.08 microg kg(-1))>PCNB (0.76 microg kg(-1))>dieldrin (0.58 microg kg(-1)). The mean residues of OCPs especially DDTs increased significantly with vegetable planting time after land use change in the first 15 years, then decreased from 20 to 30 years and increased a little afterward. The time under anaerobic and aerobic conditions was suggested to control mainly the change of the residues of OCPs.