| Polycyclic Aromatic Hydrocarbons(PAHs)are semi-volatile,toxic,bioaccumulative and persistent.They are widely found in various environmental media and can be enriched in living organisms along food chains and food networks.The dangers of the environment and human health are increasingly prominent.PAHs migrate globally along with atmospheric circulation,and “evaporation-sedimentation ” occurs continuously during the migration process,and eventually deposits in remote areas such as polar regions and high mountains.The southeastern Tibet has a unique geographical advantage such as high altitude,high forest coverage and sparse population.It has a favorable advantage for the study of PAHs,and can better understand the migration law of PAHs and the pollution degree of fragile ecosystems.At the same time,it also supplements the pollution distribution of PAHs in forest soils nationwide.This thesis focuses on the profile distribution characteristics of PAHs in several types of forest soils in southeastern Tibet and the ecological risks caused by them.Considering that different types of forests affect the environmental behaviors of PAHs,enrichment,migration and degradation in the soil,this study collected soil samples from four forest types: alpine oak,fir forest,birch forest and spruce forest.And two grassland soil samples(for control studies),the accelerated solvent extraction method(ASE)was used to extract PAHs from soil samples,and then qualitative and quantitative determination of samples by GC-MS to analyze the profile of PAHs in different forest soil samples.The distribution of PAHs in soil samples of different forest layers,the distribution of PAHs of different components along the forest soil profiles,the vertical migration characteristics of forest soil,the influencing factors and the ecological risk caused by PAHs on forest soil were analyzed.The results showed that the concentrations of total PAHs in alpine oak forest,fir forest,birch forest and spruce forest were between 131-1272 ng/g,and the average concentration was 737 ng/g,which was consistent with the relevant reports in the region..The distribution of total PAHs in different forest soil profiles was different.PAHs were enriched and fixed in the soil humus layer in the alpine and birch forest soils.The PAHs in the fir forest soil were higher in the mineral layer,spruce has an increase in the concentration of PAHs at the interface between the humus layer and the mineral layer.The results showed that there were differences in the enrichment and fixation ability of PAHs in different forest soils.This was related to the organic matter,water content and microbial degradation of forest soil.The organic matter could adsorb PAHs,and the change of nitrogen content affected the degradation of PAHs by microorganisms.In addition,PAHs can migrate along the vertical direction of forest soil by leaching.Finally,this paper uses the classification of pollution levels of PAHs and finds that PAHsin all forest soils are heavily polluted in the grassland of southeastern Tibet.Therefore,the ecological risk assessment of PAHs for vulnerable forest systems in southeastern Tibet should be paid attention to.In this paper,by using the toxicity of Bap with the highest carcinogenicity,the total toxicity value of PAHs to forest soil was calculated by using Toxic Equivalent Quantity(TEQBap),and the total toxicity of PAHs in forest soil and PAHs were found in forest soil.The content in the is consistent.Furthermore,the predictable effect concentration in forest soil can be used to evaluate the biotoxicity of PAHs,and the ecological risk assessment method of PAHs in forest soil is extended.The results of the study are expected to provide data support for the prevention and control of PAHs pollution in forest soils,especially the fragile ecosystem pollution prevention in southeastern Tibet,and provide reference for the development of PAHs forest soil pollution prevention and ecological restoration strategies. |
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