Depositional Records,Sources And Responses To Human Activities Of Polycyclic Aromatic Hydrocarbons(PAHs) In The Sediments Of Dianchi Lake And Fuxian Lake,China

Polycyclic aromatic hydrocarbons（PAHs）are hydrocarbons composed of two or more benzene rings.As a typical persistent organic pollutant（POPs）,they are ubiquitous in the environment.Once released,it will exist in the environment for a long time and will be transferred over long distances.Among them,16 PAHs are listed as priority pollutants by the US Environmental Protection Agency,and are the subject of this study.Dianchi lake is the largest freshwater lake in yunnan,is an important water source of kunming,life and production water,deep fuxian lake is China’s largest freshwater lake,rapid urbanization and industrialization,making them,such as industrial and agricultural development,the influence of human activities such as deforestation and the tourism industry,led to dianchi lake became one of the most polluted lakes in China,fuxian lake basin also varying degrees of contamination.The study of dianchi lake and Fuxian Lake sediments provides a strong theoretical basis for the understanding and management of the relationship between local environmental quality and human activities.This paper mainly studies the sedimentary records,composition characteristics,influencing factors and risk degree of PAHs in the sediments of Dianchi Lake and Fuxian Lake.The pollution status of PAHs in the sedimentary columns of Dianchi Lake and Fuxian Lake was comprehensively evaluated,and the historical change law was understood in combination with economic indicators.The influencing factors of the occurrence of PAHs in sediments were discussed,and the ecological risk of PAHs in lake sediments was evaluated.The main research conclusions are as follows:（1）Through the radionuclide dating method,the pollution history ofΣPAH₁₆ in the sedimentary columns of Dianchi Lake and Fuxian Lake in the past 100 years has been reconstructed.The total polycyclic aromatic hydrocarbon content（ΣPAH16）of Dianchi sedimentary columns DC1,DC2,and DC3(ΣPAH₁₆)ranges from172.2245ng/g,500-2145ng/g and 373-1147ng/g.The concentration ofΣPAH16 in each sedimentation column is DC1>DC2>DC3.The concentration of polycyclic aromatic hydrocarbons showed a downward trend from north to south.The distribution range ofΣPAH₁₆ content in FX1 sedimentation column is 68-821ng/g.Moreover,population,GDP and energy consumption are the main factors affecting the content ofΣPAH₁₆ in the two lake sedimentary columns.From the perspective of PAHs composition,from the bottom to the surface layer,the proportion of 2-3 ring PAHs in the sedimentary columns of Dianchi Lake and Fuxian Lake gradually decreased,and the proportion of 4 ring and 5-6 ring PAHs gradually increased.Studies have shown that the concentration of PAHs in the 2-3 ring is mainly related to human activities such as low-temperature combustion such as biomass or household coal burning.The concentration of PAHs in the 4 ring is mainly affected by coal consumption,and the PAHs in the 5-6 ring is mainly related to car exhaust emissions.The changing trend ofΣPAH₁₆ concentration in the pore water of the sedimentary columns of Dianchi Lake and Fuxian Lake in the past century is basically the same as that in the sediments.Compared with other lakes in China,the pollution level of PAHs in the sedimentary column of Dianchi Lake is at a relatively high level,and the pollution level of Fuxian Lake is at a medium level.Compared with foreign developed countries,the peak deposition time of PAHs in the sediments of Dianchi Lake and Fuxian Lake is significantly later than that of developed countries,and the concentration level is also significantly lower than that of developed countries.（2）The contents of TOC,TN and TP in the sedimentary columns of Dianchi Lake and Fuxian Lake are important influencing factors of PAHs content,and the effect of TOC and TN content on PAHs is greater than that of TP,and high-ring PAHs are correlated with TOC,TN and TP The sex is more significant than low-loop PAHs.The dominant meteorological factor of PAHs in each sedimentary column of Dianchi Lake is the average temperature,and the average annual precipitation has the smallest impact on each sedimentary column;the dominant meteorological factor of PAHs in the sedimentary column of Fuxian Lake is daily precipitation≥0.1mm days,While the average temperature and average wind speed have almost no effect.（3）The ratio method and PMF model to determine the source of PAHs in the Dianchi and Fuxian Lake sedimentary columns showed that the PAHs in the Dianchi DC1 sedimentary column were mainly traffic sources,contributing 47%,and the DC2sedimentary column was also mainly traffic sources.The amount of DC3 is 47%.The main source of DC3 is coal combustion,with a contribution of 29%.There is a trend of transition from coal and biomass combustion sources to fossil fuel combustion sources in the source of PAHs in each sedimentary column from the bottom to the surface;Fuxian The source of PAHs in lake sedimentary pillars was mainly biomass combustion sources before 1978,contributing 34%,and after 1978,mainly coal combustion sources,contributing 32%.（4）The concentrations of TEQ_{Ba P} and MEQ_{Ba P} in the sedimentary columns of Dianchi Lake are at a low toxicity level,and the risk of carcinogenesis and teratogenesis are not high.The concentrations of TEQ_{Ba P} and MEQ_{Ba P} in the sedimentary column FX1 of Fuxian Lake are at a low toxicity level,and there is basically no potential carcinogenic or teratogenic risk.In the pore water of each sedimentary column of Dianchi Lake,the pollution degree of PAHs in the 2-3 ring is relatively light,while the PAHs in the 4-6 ring is more polluted;in the pore water of Fuxian Lake,the pollution of the PAHs in the 2-3 ring is also light.The concentrations of the 4-6 ring polycyclic aromatic hydrocarbons are mostly within the safe value range,and only a small part has reached its chronic toxicity level,and the overall pollution is relatively light.（5）The neural network model predicts the concentration of PAHs in the sedimentary pillars of Dianchi Lake and Fuxian Lake from 2021 to 2030.The results show that the concentration of PAHs in the sediments of Dianchi Lake in the next ten years will not increase significantly,and the highest concentration is 2128.9 ng/g.The concentration of PAHs in sediments will be basically stable in the next ten years,and will not increase significantly,with a maximum value of 814.4 ng/g.The predicted concentration data of the two lakes have not increased significantly,but the government still needs to pay attention and adopt corresponding environmental protection measures to avoid lake pollution problems.