Source Analysis And Toxicity Risk Assessment Of Polycyclic Aromatic Hydrocarbons In Lake Sediments In The Erhai Lake Basin

With the rapid advancement of urbanization,the increase of population and the development of transportation and tourism,the water environment quality of the lakes in the Erhai Lake basin has decreased obviously,and there are different degrees of pollution.There are many industrial and agricultural activities in the basin.The lake is dominated by non-point source pollution,while the point source pollution focuses on industrial pollution,accommodation and tourism activities along the lake.As the main lake in the basin,Erhai Lake is a large and medium-sized shallow lake,with more surrounding towns and more rivers entering the lake,so the pressure of environmental pollution is high and the degree of pollution is large.As a deep plateau lake surrounded by mountains,the water quality of the lake is good because of its extensive karst landforms.Xihu Lake is a small lake with weak pollution resistance,good ecological environment and deep peat layer(it is a plateau peat lake wetland).Polycyclic aromatic hydrocarbons(PAHs)are mainly derived from human combustion sources.They are highly toxic,difficult to degrade,and widely exist in the environment,and They are easily deposited in sediments.The content and composition of PAHs in lake sediments under the influence of different environmental types and human activities are significantly different.The analysis of PAHs concentration and toxicity in sediments from the perspective of the whole basin can clarify the importance of different sources and influencing factors.It can provide some reference basis for the ecological risk of PAHs in different types of lake media.Among the three lakes in the Erhai Lake basin,the concentration of PAHs and toxic equivalent quantity(TEQ)in the sediments of Erhai Lake are the highest,which is due to the large area of Erhai Lake,the high pollution pressure caused by intensive human activities around it,and the lowest pollution level of PAHs in Xihu Lake.According to the pollution assessment standard of PAHs in water sediments,most of the surface sediments of Erhai Lake are in a state of high pollution,and PAHs in three lake sediment columns are in a moderate pollution level.The high concentrations of PAHs and TEQ levels in Erhai Lake were correlated with the frequent urban activities in nearby Dali City.The temporal variation trend and peak time of PAHs and TEQ are the response of human activities in different regions to some extent.Among the three lakes in the Erhai Lake Basin,the concentration and TEQ content of PAHs in the sediments of Erhai Lake is the highest,which is due to the large area of Erhai Lake,the high pollution pressure caused by the intensive human activities around it.According to the pollution assessment standard of PAHs in water sediments,most of the surface sediments of Erhai Lake are in a state of high pollution,and PAHs in three lake sediment cores are in a moderate pollution level.PAHs pollution in Xihu Lake is the lowest.The high concentrations and TEQ of PAHs levels in Erhai Lake are correlated with the frequent urban activities in nearby Dali City.The temporal variation trend and peak time of concentrations and TEQ of PAHs are the response of human activities in different regions to some extent.(1)Low molecular weight PAHs(LMW-PAHs)were the main PAHs in the lake sediments of Erhai Lake basin,and BAP made the biggest contribution to TEQ,which was related to the source and influencing factors of PAHs.LMW-PAHs are mainly from long-distance atmospheric transport,and the decreasing proportion of LMW-PAHs indicates that PAHs in lake sediments are more affected by local environment and come from Moderate molecular weight PAHs(MMW-PAHs)and High molecular weight PAHs(HMW-PAHs)increased.The PAHs in the surface sediments of Erhai Lake are mainly from the mixed sources of combustion.Further analysis by positive matrix factorization(PMF)shows that the contributions of coal and biomass combustion,fossil fuel combustion,transportation sources and industrial coal combustion in the surface sediments are relatively uniform.The source types of PAHs in each sediment core are similar,but the time variation trend is different,but the contribution of high-temperature combustion sources shows an overall increasing trend.The PAHs in the surface sediments and sediment cores are mainly low molecular weight-PAHs,and the biggest contribution to TEQ is Ba P,which is related to the different sources of PAHs.LMW-PAHs are mainly from long-distance atmospheric transport,and their proportion decreases year by year,indicating that PAHs in lake sediments are more affected by local environment.The PAHs in the sediments of three lakes in the basin are mainly derived from combustion sources.According to the isomers,the PAHs in the surface sediments of Erhai Lake are mainly derived from the mixed sources of coal and biomass combustion and petroleum combustion.PMF further analyzed the surface sediments.The contribution of China's coal and biomass combustion,petroleum combustion,transportation sources and industrial coal combustion sources is relatively even.The source analysis of the three sediment cores is similar,but the time changes are different.The source of PAHs in the Erhai sediment core changed to petroleum combustion,the source of PAHs in the Cibihu Lake changed to the combustion mixed source,the sediments of Cibihu Lake turned to combustion source,and PAHs from the sediments of Xihu Lake tend to come from high temperature combustion.(2)Total organic carbon(TOC)and Total nitrogen(TN)in surface sediments of Erhai Lake,sediment cores of Erhai Lake and Xihu Lake were significantly positively correlated with?₁₆PAHs and TEQ.The results show that TOC,TN and PAHs are discharged together with wastewater or from non-point sources in the basin.In addition,under the action of biological pump,planktonic algae in the lake consume POPs in the water body,and then play a medium role in the sediments through adsorption and deposition from the air,resulting in the continuous occurrence and accumulation of PAHs in the sediments under the eutrophic state of the water body.Therefore,TOC and TN in lake sediments are important factors affecting PAHs pollution distribution,and can also indicate the carcinogenicity of PAHs in sediments to a certain extent.In addition,TEQ was highly correlated with local GDP,population and energy consumption,indicating that PAHs and its toxic pollution were strongly influenced by human activities.(3)In addition to toxicity equivalent,the ecological risk of PAHs in lake sediments in the Erhai Lake Basin was effectively evaluated according to biological effect value and entropy method,which indicated that the ecological risk of PAHs in lake sediments in the Erhai Basin was low.The ecological risk in the sediment column of Erhai Lake is higher than that in Cibihu Lake and Xihu Lake as well as in the surface sediments.PAHs may cause high toxic damage to the ecosystem,and more attention should be paid to the ecological damage of some PAHs.There are various types of lakes in Erhai Basin,which are the important basis for local economic development and people's life.At present,there are many studies on the distribution of PAHs in various media of lake ecological environment in China.This study analyzed and compared the distribution characteristics of PAHs and their toxicity in sediments of different lakes in Erhai Basin from the perspective of the whole basin.It can provide some reference basis for the ecological risk of PAHs in different types of lake media.