DDTs and HCHs in sediment cores from the Tibetan Plateau.

Sediment cores were collected from five critical regions in the Tibetan Plateau and were analysed for OCPs with the objective of examining the time trends and recycling of DDTs and HCHs in the cryogenic area. A concurrent increase of the DDT and HCH concentrations from the late 1980s in Lake Yamzho Yumco, Nam Co and Star Sea were observed. The increasing levels of DDE/DDTs (>0.4) suggested that DDT in the upper layers of the sediment cores may be recycled/"weathered" DDT. Regarding the acceleration of glacier retreat from the 1980s due to global warming, it is suggested that OCPs formerly trapped either in the snow/glacier or in the frozen soil land recently reclaimed in the processes of glacier retreat may have been flushed into the sedimentary basins. These findings demonstrate the potential impact of global warming on the recycling of POPs in the plateau cryosphere and indicate that the pristine Tibetan Plateau may serve as one of the key probes to the global trend of POPs.