Distribution and Source Analysis of Polycyclic Aromatic Hydrocarbons (PAHs) and Organochlorine Pesticides (OCPs) in Soils from Shergyla Mountain, Southeast Tibetan Plateau

Abstract

Soils were collected from Shergyla Mountain shade slope and south-facing slope in southeast Tibetan Plateau (TP) in August 2012 and they were measured for polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs)(including HCHs and DDTs). The concentrations of ∑16PAHs ranged from 99.3 to 1984 ng·g-1 dw, with a mean value of 1017 ng·g-1 dw. HCHs and DDTs in soils samples were in the range of 0.37-2.07 ng·g-1 dw (mean 1.15 ng·g-1 dw) and 0.70-43.9 ng·g-1 dw (mean 9.87 ng·g-1 dw), respectively. The concentrations of all measured compounds were much higher than those in central or western TP,and the PAHs concentration was even up to two orders of magnitude. The concentrations of α-HCH and DDTs in south-facing slope increased with altitude, but HCHs and DDTs in shade slope had no significant correlation with altitude. There was no consistent increasing or decreasing trend of PAHs in shade slope with altitude, and the concentrations of PAHs in south-facing slope showed a higher value in lower altitude, indicating the existence of local pollution emissions. The PAHs profile was dominated by lighter constituents (2 & 3-ring accounted for higher than 85%),inferring that the PAHs in the study area were largely influenced by long range atmospheric transport (LRAT) of pollutants. The special diagnostic ratios of PAHs suggested that PAHs were mainly produced by low temperature combustion of biomass and fossil fuels, except that two sampling sites of shade slope had been possibly influenced by oil residue. The relatively low ratios of α/γ-HCH inferred HCHs in the research area was the result of the combined contribution of the historical technical HCHs and Lindan. The ratios of p,p'-DDE/p,p'-DDT and o,p'-DDT/p,p'-DDT indicated DDTs were from the combined contribution of the historical technical DDTs and dicofol. According to the profile of PAHs, HCHs and DDTs and the meteorological conditions of Shergyla Mountain, the transport of PAHs and OCPs in the study area was mainly influenced by the Indian Monsoon.