Evidence for persistent organic pollutants released from melting glacier in the central Tibetan Plateau, China.

Glacier alluvial deposits record persistent organic pollutants (POPs) not only derived from the atmospheric deposition but also from the release of glacial melting. The evidence for melting glacier in the Tibetan Plateau (TP) as a secondary source of pollutants is introduced through investigating the concentration of organochlorine pesticides (OCPs) in four deposited profiles collected at the edge of the Changwengluozha glacier. Two concentration peaks were observed for dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) in the past century. The first peak was observed in the 1970s, corresponding with the heavy usage of HCHs and DDTs in the surrounding countries and regions. The second one was in 2000 when the production and usage of DDTs and HCHs were strictly limited, which possibly indicated a significant release from melting glacier. This result was further supported by the enantiomeric fraction values for α-HCH and o,p'-DDT. On the other hand, the dramatic increase of polycyclic aromatic hydrocarbons (PAHs) from atmospheric deposition, which was associated with the socioeconomic development in Tibet, shaded the release of PAHs from melting glacier. This study reveals not only the air deposition history of legacy POPs but also a substantial release of OCPs from glacier to the adjacent environment. Our research supports the hypothesis that the melting glacier in the TP represents a secondary source of OCPs, which is consistent with the findings in the Alps glaciers.