Organochlorine Pesticides (OCPs) in Soils Along the Eastern Slope of the Tibetan Plateau

Abstract

Soil samples collected from several sites along an altitudinal transect on the eastern slope of the Tibetan Plateau were analyzed for hexachlorobenzenes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs). The results showed that HCHs and DDTs were found in the soil samples from the remote high altitude areas away from source regions, which confirmed the long-range atmospheric transport phenomenon of these organochlorine pesticides (OCPs) insecticides. The OCP concentrations in the soils had a significant negative correlation with altitude; they showed a trend to increase with decreasing altitude, but the increase was not continuous, being interrupted at some moderate-altitude sites on the transect. The distances from the source region, landforms, soil properties, and physical-chemical properties of OCPs were more important than total organic carbon content to the distribution of OCPs in soils disturbed by human activities. An analysis of the compositions of HCH isomers and DDTs revealed predominantly low ratios of CK-HCH to 7-HCH, ranging from 0.06 to 4.79, which suggested current lindane inputs. On the other hand, low p,p'-DDT/ p,p'-DDE and o,p'-DDT/ p,p'-DDT ratios were observed, indicating mainly aged historical DDT residues in the study area.