Study On The Distribution And Source And Ecological Risk Of Typical Persistent Toxic Pollutants In Lakes

Supported by the National Science and Technology Basic Work Project "Investigation of Toxic and Hazardous Chemicals and Water Environment in Typical Lakes(2015FY110900)",the distribution characteristics,sources and ecological risks of heavy metals,PAHs and OCPs in water bodies and sediments of typical lakes in the middle and lower reaches of Yangtze River,such as Liangzi Lake and Danjiangkou Reservoir,were studied comprehensively in this paper.A unified method for the rapid detection of PAHs and OCPs in water and sediment samples was developed,and the pretreatment methods for water and sediment samples were optimized by orthogonal experiments: for water samples,the SPE pretreatment method was based on a C18 SPE column with a 1:1 volume ratio of dichloromethane/hexane as eluent;for sediment samples,a non-polar PDMS extraction method was used.For the sediment samples,the non-polar PDMS extraction and 60℃/60 min SPME pretreatment method were used to extract and recover 44 compounds from the lake water samples and sediments,and the relative standard deviation of the standard samples was kept within 20%,while the recoveries ranged from 73.68% to 119.24%,meeting the quality control requirements.According to the existing water area and topographic conditions of Liangzi Lake and Danjiangkou Reservoir,15 sampling points of Liangzi Lake and 22 sampling points of Danjiangkou Reservoir were obtained in the reservoir area by the square grid method and in the river by the equidistant method,respectively,and water and sediment samples were collected twice in 2019 and 2020 for testing and analysis.The results showed that the overall content of heavy metals,PAHs and organochlorine pesticides in Liangzi Lake and Danjiangkou Reservoir was low,and there were no special exceeding elements compared with the standard limit values and other domestic water environment testing values.At the same time,the detection of each indicator in the water body is lower than that in the sediment,and the content is significantly lower than that in the sediment,which is the main reservoir of typical PTS in each lake and is the main source of pollutant release in the water body.The distribution of heavy metals,polycyclic aromatic hydrocarbons and organochlorine pesticides in Liangzi Lake and Danjiangkou Reservoir were analyzed by box distribution map and GIS map of geostatistical analysis,and the results showed that the pollutants in the water bodies of the lakes in the two years of 2019-2020 showed an overall decrease in the content of heavy metals and an overall increase in the content of polycyclic aromatic hydrocarbons compared with the previous year,while the organochlorine pesticides had fluctuations in the proportion of isomers due to the degradation of the main components.The GIS map of ground statistical analysis shows that there are two characteristics of pollution distribution,point source and surface source distribution,mainly point source distribution.The distribution of pollutants is concentrated in the mouth of the tributary and the center of the reservoir area,while there is a transfer of pollution in the areas where the coastal residents gather,pollution is basically foreign confluence,and the influence of tributary confluence is greater.The sediment sources of heavy metals,polycyclic aromatic hydrocarbons(PAHs)and organochlorine pesticides in Liangzi Lake and Danjiangkou Reservoir were identified by principal component analysis,characteristic ratio method and isomeric ratio method respectively.The burning sources of PAHs are mainly fossil fuels,and there are wood and coal burning sources in the coastal forest and farmland areas,and some of the sample sites in the tributaries into the lake show petroleum emission sources;the sediment BHCs,DDTs,endosulfan and chlordane OCPs in Liangzi Lake and Danjiangkou Reservoir are mainly historical emission residues,and there is a gradual degradation phenomenon,and the OCPs are enriched in the central part of the lake and the coastal areas by farmland and forest.The overall risk of sediment PTS in the two lakes(reservoirs)is mainly influenced by OCPs: the overall risk of heavy metals is low,and the main risk elements are As and Pb,Zn and Cu,and the future risk control needs to pay attention to the production and living discharges of coastal residential areas.The overall risk of polycyclic aromatic hydrocarbons(PAHs)is basically low,and the main risk elements are Nap,Flo and Phe,and the future risk control needs to pay attention to coastal combustion fumes and fuel oil emissions.In the future risk control,special attention should be paid to their bioaccumulation effects and foreign input control.