Study On The Pollution Mechanism Of Perfluorinated Compounds In Shallow Groundwater System Of A Chemical Industrial Park

Perfluorinated compounds are a group of new organic pollutants with bioaccumulation and persistence,commonly referred to as PFCs.PFCs have reproductive toxicity and mutagenic toxicity,which can damage the human liver,cardiovascular,thyroid and the existence of potential carcinogenicity.The pollution of PFCs in groundwater system has become more and more serious,attracting people’s attention on a global scale.At present,PFOA,PFBA and PFHpA are the main measured PFCs in the shallow groundwater system of our country.In this paper,two fluoride chemical industrial parks in the upper reaches and the middle reaches of Xiaoqing river basin are taken as the research area.Through the work of hydrogeological survey,shallow groundwater level monitoring,sampling of characteristic monitoring points and the detection of PFCs concentration in the study area,the spatial and temporal distribution characteristics of PFCs in the shallow groundwater system are analyzed,and then the pollution mechanism of PFCs in the shallow groundwater system is studied.The main conclusions are as follows:(1)In the upper reaches of Xiaoqing River,195 water level monitoring points were set up in the study area,of which 37 sampling wells were selected.Twelve PFCs were detected in the water samples collected in this study area: PFBS,PFOA,PFHxS,PFHpA,PFPeA,PFDA,PFNA,PFUnDA,PFDoDA,PFBA,PFHxA,PFOS.The concentration of PFCs detected in the wet season was 0.27 ng / L-922.20 ng / L,and the dry season was 0.75 ng / L-768.50 ng / L.The highest concentration of PFOA was detected in 37 samples,and the detection rate was 100%.The overall groundwater flow in this area is from south to north along Zhangqi River to Xiaoqing River.There are perennial groundwater funnels in shallow groundwater systems in the area.The pollution plume of PFCs takes the No.8 sampling well in the chemical industry park as the center,which is oval in shape and diffuses to the northwest faster.The results show that the spatial distribution of PFCs in the shallow groundwater system in the study area is mainly affected by the groundwater flow and groundwater funnel traction.The time distribution of PFCs is closely related to the groundwater level.When the dry season and the wet season alternate,the concentration of PFCs in the area where the groundwater level rises rapidly is large and the change of the PFCs in the area where the groundwater level fluctuates is small.The reason for this phenomenon is that when the flood season is approaching,rainfall increases,and PFCs in the soil are leached into the shallow groundwater system by leaching,and the areas where the water level rises rapidly will dissolve the PFCs in the aeration zone by dissolving Into the groundwater system,resulting in higher concentrations of PFCs in the wet season than in the dry season.(2)In the middle reaches of Xiaoqing River,140 water level monitoring points were set up in the study area,of which 34 monitoring points were selected as water level sampling points.Twelve PFCs(PFBS,PFOA,PFHxS,PFHpA,PFPeA,PFDA,PFNA,PFUnDA,PFDoDA,PFBA,PFHxA,PFOS)were also detected in the collected water samples.PFCs concentration was 0.002μg / L-418.300μg / L in the wet season,and 0.002μg / L-232.39μg / L in the dry season.The highest concentration of PFOA was detected in all 34 samples,and the detection rate was 100%.The groundwater flow in this area goes north along the East Longzhu River and emerges from the lake in the northern part of the study area.There are also two groundwater funnels in the shallow groundwater system in the study area,which are located respectively in the northwest and the east of the study area.Pollution plumes of PFCs Take sampling well No.27 as the pollution center,distributed in an elongated shape from south to north.The spatial distribution characteristics of PFCs are mainly formed under the action of shallow groundwater flow.At the same time,the groundwater funnel also has certain traction on the pollution distribution of PFCs.The time distribution of PFCs is mainly related to the change of groundwater level.In the funnel area in the northwestern part of the study area where the groundwater level changes greatly,the concentration in the wet season is 3.7 times that in the dry season,while the concentration in the wet season in other regions where the water level changes little is Low season 1.3-1.7 times.Draw the conclusion that the temporal distribution of PFCs pollution is mainly related to the groundwater level,a two-dimensional non-isotropic flow model is established in the study area of the middle reaches of Xiaoqing River,on the basis of which a solute transport Model to better predict the PFCs pollution migration rules.