Evidence of local emission of organochlorine pesticides in the Tibetan plateau

Organochlorine pesticides (OCPs) including DDTs, HCHs, chlordanes and hexachlorobenzene (HCB) in the atmosphere of Lhasa, the capital city of Tibet, China, were monitored in an attempt to assess their concentration level and potential sources. Twenty air samples collected at two sites in Lhasa between 6 and 11 August 2006 were analyzed for OCPs. The mean concentrations of α-, γ-HCHs, HCB, trans-chlordane (TC), cis-chlordane (CC), p,p′-DDE, p,p′-DDD, o,p′-DDT, and p,p′-DDT were 49, 163, 182, 204, 128, 122, 46, 206, and 114 pg/m3, respectively. The relatively low α-HCH/γ-HCH ratios indicated that lindane is the current source of HCHs in Lhasa. A TC/CC ratio of ≈1.2 was observed for samples with relatively high chlordane concentrations, suggesting a current local use of technical chlordane. The isomer ratios of DDTs also implied present usages of DDT-containing dicofol and technical DDT in the city. Contrary to other OCPs, HCB displayed higher concentrations during nighttime than daytime, indicative of a dominant contribution from local combustion. We conclude that current use and local emissions may be important sources for OCPs in Lhasa and may contribute to OCP contamination in the environment of the populated agricultural Lahsa River basin.