Concentrations and source identification of organochlorine pesticides (OCPs) in soils from Wolong Natural Reserve

In order to understand the distribution profile, composition characteristics and sources of OCPs, soil samples collected from Wolong Natural Reserve (WNR) in spring and autumn in 2005 were analyzed using gas chromatography coupled with electron capture detector (GC-ECD). Results showed that all OCPs concentrations were in the range of 10(-2) ng/g-10(-1) ng/g, representing the background level in those remote sites. Generally, their concentrations were slightly higher in spring than in autumn, which could be explained by OCPs: 1) may be released to soil from snow-melting water in spring; 2) partially evaporate into air from soil due to high temperature and intense radiation in summer and 3) can be relatively high degradation rate in summer. There were notable differences of OCPs seasonal variations between samples from alpine meadow and those from under-treeline. This phenomenon was related to physical-chemical properties of OCPs and vegetation coverage. For alpine meadow soils, levels of OCPs were increased with increasing altitudinal gradient, which was associated with enhanced scavenging efficiency of wet precipitation. Composition characteristics of OCPs in soils were similar to those of air samples, which was distinct from those of typical contaminated soils, indicating that OCPs in WNR soils were mainly from atmospheric transport.