Currently used organochlorine pesticides in Mianzhu—Aba prefecture transect, eastern of the Tibetan Plateau, western China

Abstract

Mianzhu—Aba prefecture transect, eastern of the Tibetan Plateau, was selected to study the occurrence of currently used organochlorine pesticides (OCPs) along an altitudinal gradient. Soil mean concentrations (ngg−1, dw) in winter (March) and summer (July) changed as follows: 0.24 and 0.27 for hexachlorobenzene (HCB), 0.15 and 0.12 for heptachlor (HEPT), 0.43 and 0.04 for heptachlor epoxide (HEPX), 0.53 and 0.11 for chlordane, 0.10 and 0.10 for nonachlor, 0.10 and 0.35 for endosulfan, respectively. Soil OCP concentrations in this transect were slightly higher than those in other mountainous regions. Analysis of some compound ratios showed that the OCPs in this transect might be partly attributed to the long-range atmospheric transport and also suggested current chlordane and endosulfan inputs. The total OCPs in winter soil (1.55ngg−1) were slightly higher than those in summer soil (0.99ngg−1), in full agreement with seasonal distribution pattern with input of new substance in winter and loss of unstable organic substance in summer. Different spatial distribution for different OCPs was observed along the transect. Individual linear regression analyses between OCP concentrations and some available variables showed that OCPs distribution along this transect were influenced by many factors, not solely a variable. A primary fugacity analysis on OCPs soil–air exchange in summer indicated that this transect may be a sink for cis-chlordane, and a secondary source for HCB and HEPT. As with trans-chlordane, α-endosulfan and β-endosulfan, this transect may be both a sink and a secondary source.