Tibet Of Pahs In Soil Content, Distribution And Source Analysis

In this study,60sites were selected in Tibet distributed in Xigaze, Ali,Naqu, Linzhi, Shannan and Lhasa, and87soil samples were collected inOctober2010. PAHs in soil Samples were firstly extracted withdichloromethane by Soxhlet, then fractionated on an alumina-silica column,and finally analyzed by Gas Chromatograph-Mass Spectrometer (GC/MS).Based on the detected data, PAHs concentrations levels in all samples havebeen reported, and its distribution and possible sources have been discussed.The conclusions were listed as follows:1. The sum of the15PAH concentrations in cultivated and raw soils were0.53~129.14ng/g,1.50~111.97ng/g, respectively. The average of the15PAHconcentrations were41.32ng/g,10.62ng/g, respectively. The concentration ofB[a] P and Phe was the highest in cultivated and raw soils. Acy was the lowestcomponent in all samples. The percent of high molecular weight PAHs (≥4ring) in cultivated and raw soils accounted for81.8%,60.0%, respectively.2. According to the soil standards in Holland, the soil was non-pollutionwhose concentration of PAHs was below50ng/g. In this study, the percent ofthis non-pollution soil accounted for95.4%. The concentrations of PAHs werelower in area of Ali and Naqu, where people were rare. The concentrations ofPAHs were higher in area of Linzhi, Shannan, Lhasa, and that close thesouthern of the national road. In those areas, where traffic was moreconvenient and the flow was heavier than the northern Tibet, people wereconcentrated and their cultivation using much chemical fertilizer and pesticidewas very frequent.3. The highest concentrations of PAHs in different vertical soils weresurface soil, followed by middle soil; the lowest was the bottom soil. Therewere some samples which the concentration of PAHs was higher in middle soilthan that in surface soil, possibly due to turning in cultivated soils. The percentof high ring PAHs accounted for large proportion, owing to its particulateexisting, not easy to transfer and easy to accumulate in soils.4. As the ratio analysis results shown, PAHs were probably come from high temperature combustion and petroleum. Principal component analysisresults showed that the main source was motor vehicle whose contributionreached75.84%and the small ratio source was biomass burning whosecontribution reached14.10%. It could be seen from the back trajectories that inWinter Tibet region had exogenous inputs which were mainly from the borderneighboring countries in central Asia.