Organochlorine pesticides and polychlorinated biphenyls in surface soils from Ruoergai high altitude prairie, east edge of Qinghai-Tibet Plateau

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in surface soils along a transect from source areas (a petro-chemical industrial city, Lanzhou and its adjacent agricultural areas) to Ruoergai highland prairie (3552 m above sea level (a.s.l.)), where livestock farming was the only human economic activity, were studied. OCPs in Ruoergai soils were dominated by HCHs. The land types, organic carbon contents and pH affected the POP preservation in soil. OCPs and PCBs in surface soils in Ruoergai wetland and grassland showed different contamination patterns; OCP levels in wetland soils were higher than those in grassland. Significant correlations were observed between total organic carbon (TOC) contents and PCB concentrations in the soils. The land type determines TOC content in soils, which in turn was a major factor on soil concentrations of POPs. The transect was divided into two sections: The first section (Gradient I) is from Lanzhou (1740 m a.s.l.) to Luqu (2400 m a.s.l.) with decreasing agricultural activities, and the second section (Gradient II) is from Luqu to Ruoergai (3500 m a.s.l.) with grassland as the main land type. Soils of Ruoergai area were dominated by α-HCH, β-HCH, HCB, and PCB28, suggesting that the behaviors of POPs in the high plateau region were different from high mountain cold-trapping effect, and that the POPs' behaviors in high plateau region were similar to Polar Regions.