Vertical Variation Of Polycyclic Aromatic Hydrocarbons In Typical Lake Sediments From The Middle And Lower Reaches Of The Yangtze River

With the rapid development of social economy and the accelerating urbanization and industrialization,the problem of environmental pollution has become increasingly prominent.Chaohu Lake,located in the central part of Anhui Province,is the fifth largest freshwater lake in China and is a famous land of fish and rice.However,since the 1980 s,Chaohu Lake has been polluted by surrounding cities,resulting in a worsening of the aquatic environment.The problem of cyanobacteria has intensified,which has aroused widespread concern in the whole society.Polycyclic aromatic hydrocarbons(PAHs)are a class of persistent organic pollutants.Due to the triad effect(teratogenic,carcinogenic and mutagenicity)of polycyclic aromatic hydrocarbons,many scholars have also conducted in-depth research on them.In this study,the sediment cores columns of the middle and lower reaches of the Yangtze River(Chaohu Lake,Daguan Lake and Longgan Lake)were selected as research objects.The detection methods,composition,concentration distribution,pollution sources and potential risks of polycyclic aromatic hydrocarbons in samples were analyzed.The vertical distribution of polycyclic aromatic hydrocarbons,composition,relationship with Toc and the main sources and ecological risks of polycyclic aromatic hydrocarbons were evaluated.The main findings are as follows:(1)The average concentrations of polycyclic aromatic hydrocarbons(PAHs)in the sediment samples of the West Lake,Chaohu Lake,Daguan Lake and Longgan Lake were 292.6ng/g,189.32 ng/g,289.34 ng/g,and 382.3 ng/g.(2)The vertical distribution of sedimentary columns in the East Lake of Chaohu Lake,the West Lake of Dahu Lake,Daguan Lake and Longgan Lake basically showed a steady and slow growth to the rapid growth and the final decline.(3)Analysis of the proportion of low,medium and high rings of polycyclic aromatic hydrocarbons in each sedimentary column.The proportions of low,medium and high rings in Chaohu East Lake,Chaohu West Lake,Daguan Lake and Longgan Lake are:35.48% and42.23% respectively.22.78%;34.91%,37.72%,29.08%;30.41%,54.00%,14.59%;39.43%,52.21%,8.36%.The analysis of the source of polycyclic aromatic hydrocarbons in the sedimentary column shows that the main sources of polycyclic aromatic hydrocarbons at the four sampling points are combustion sources,and there is little pollution directly from petroleum.(4)Evaluation of the ecological risk of polycyclic aromatic hydrocarbons in sedimentary columns(5)A linear relationship between polycyclic aromatic hydrocarbon content and TOC in each sedimentary column shows that only the polycyclic aromatic hydrocarbon content(TOC)in the Xichao Lake sample has a significant positive correlation,which proves that the polycyclic aromatic hydrocarbon content in Xichaohu Lake is controlled by TOC.The content of polycyclic aromatic hydrocarbons in the remaining sedimentary column samples was not significantly correlated with TOC.