Altitudinal and spatial signature of persistent organic pollutants in soil, lichen, conifer needles, and bark of the southeast Tibetan Plateau: implications for sources and environmental cycling

Abstract

The southeast Tibetan Plateau (TP) of China is characterized by mountain-valley topography and is usually the main channel for the warm and humid airstream from South Asia caused by the Indian monsoon. In this study, it is hypothesized that some semivolatile organic pollutants such as organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) can be transported from the densely populated and intensely agricultural Indian Subcontinent via the Indian monsoon and then cold-trapped by the mountains of the southeast TP. Samples of soils, lichens, conifer barks, and needles were collected from five transects to investigate the accumulation patterns of OCPs and PAHs in this region. The OCP concentrations were found to generally increase with increasing altitude in transects 1, 3, and 4, while such trends were insignificant in most cases for PAHs. Total organic carbon/lipid based normalization of concentrations does not strengthen the correlations with altitude in most cases. Chemical concentration ratios in soils of forest areas to clearing sites without forest cover (F/C) showed significantly positive correlation with log K(oa) and negative correlation with log K(aw) of PAHs, suggesting that the role of forests as a filter and forest soil as a final sink are more pronounced for more lipophilic compounds. A lower α-/γ-HCH ratio and higher ratios of DDT/DDE and o,p'-DDT/p,p'-DDT compared with the technical products suggest the usage of lindane (γ-HCH), DDT, and dicofol in neighboring countries. The suitability of using different sample matrices (soil, lichen, conifer bark, and needles) as passive air samplers in remote regions is evaluated.