Accumulation And Fate Processes Of Organochlorine Pesticides In Soil Profiles In Mt.Shergyla,Southeast Tibetan Plateau: A Comparison On Different Forest Types

POPs(persistent organic pollutants)are characterized by high toxicity,carcinogenicity,persistence and bioaccumulation through the food chain,and thus have potential risks to alpine ecosystems and human health.It is difficult for POPs to decompose in natural environment,thus it could exist in the environment for long time.These semi-volatile compounds could be transported through the atmosphere and river.During the transport process,volatilization and deposition happen all the time,and at last,POPs are transported to global in many environmental matrices(such as soil,water,vegetation and atmosphere).The previous works found that forest plays a very important role in POPs global fates,the forest filter effect could be effective to remove the POPs in atmosphere into soil.Tibetan Plateau is called the third pole of the world with a mean altitude of about 4000 meters above the sea level(m,a.s.l.)and it was believed to be an indicator region to study LRAT behavior of POPs since there are limited local sources.In addition,due to the summer Indian monsoon,the southeast Tibetan Plateau gains abundant rainfall,and thus vast land surface are covered by multiple vegetation.The diversity and richness of vegetation,in addition to the high elevation jointly could enhance deposition of POPs,and thus southeast Tibetan Plateau became a natural laboratory for studying POPs.All in all,POPs fate was influenced by complex parameters,such as land cover,topography,soil property and meteorological conditions.In this study,we selected four forest sites adjacent to each other with different dominant tree species in Mt.Shergyla of the southeast Tibetan Plateau at the similar altitude(3418-3475m),and two adjacent reference sites without forest cover for comparison,and soil samples and fresh leaf samples were collected.The objective of this study was to investigate the influence of different forest types on the fate of OCPs.In this study,the concentration of OCPs in forest soilwas higher than that in clearing sites indicated that forest filter effect enhanced the process of transporting POPs from air to soil.The distribution of OCPs in soil was affected by TOC content,and OCPs mainly stored in humus layer(higher TOC content).Higher capacity of accumulation of OCPs were observed in birch and fir forests when compared to other forests,and fir forest seems more likely to accumulate HCHs while birch forest is more likely to accumulate DDTs.In addition,we noticed that OCPs have relatively higher mobility in broadleaved forest soils,especially in birch profile though the transport by leaching was limited.At last,the result on air-to-ground fluxes may indicated that birch and fir forests could remove more OCPs from air than other two forests.