Fate And Bioaccumulation Of Polycylic Aromatic Hydrocarbons In Multi-media Environment In Dianshan Lake,Shanghai

Dianshan Lake is the largest natural freshwater lake in Shanghai and an important water source protection area in the upper reaches of Huangpu River.The area around Dianshan Lake is one of the more dynamic areas for investment growth and social development in the Taihu Lake basin.With the development of regional social economy,the total amount and types of pollutant emissions tend to rise,and the environmental pollution problem keeps coming to the fore.Polycyclic Aromatic Hydrocarbons（PAHs）are a class of organic pollutants produced by natural or human activities that can be transported and deposited over long distances by air,accumulate in terrestrial and aquatic ecosystems,and pose potential threats to environmental quality and human health.Considering the harmfulness of such pollutants and the lack of research on the environmental behavior of anthropogenic PAHs in the Dianshan Lake area,this paper conducted a systematic study on the multi-media environmental behavior of PAHs in Dianshan Lake in order to provide a scientific basis for the prevention and control of PAHs pollution in shallow water lakes.14 sampling sites were set up in Dianshan Lake in five environmental phases,including atmosphere（dissolved and particle phases）,water（dissolved and particle phases）and sediment,and 19 aquatic animals such as fish,shrimp,crab and shellfish,were collected,and the contents of 16 PAHs were determined by GC-MS.Based on this,the distribution composition and influence factors of PAHs in the multi-media phases in shallow lake ecosystem were studied,and a class III fugacity model was used to simulate their multi-media migration and homing behavior.The bioaccumulation,tissue distribution and food web transfer behaviors of PAHs in aquatic organisms,the sources and health risks of PAHs were assessed using the Positive Matrix Factor（PMF）model and Lifetime Carcinogenic Risk（ILCRs）,and the following main insights were obtained.The results of this research are as follows:（1）The concentration of atmospheric PAHs in Dianshan Lake ranged from 15.43to 170.61 ng/m³,with a mean value of 110.12 ng/m³,normal season>dry season>wet season,in which the atmospheric PAHs are mainly distributed in the atmospheric dissolved phase.The dissolved phase PAHs in the water of Dianshan Lake is ranked as dry season>normal season>wet season,and the PAHs at the inlet and outlet sites are higher than those at other locations in the lake body.3-ring Phenanthrene（Phe）has the highest concentration in the dissolved phase,and low-ring PAHs（LMW-PAHs）are the most dominant component,and the concentration of PAHs in the particle phase of the water of Dianshan Lake is higher in dry season,followed by wet season,and normal season,in which the average PAHs concentration difference between wet season and normal season is small,and the spatial concentration difference of PAHs is:outgoing rivers>lake body>incoming rivers.The characteristics of PAHs components in the particle phase were similar to those in the dissolved phase,and the proportion of LMW-PAHs increased.The particle-water partition coefficient K_p indicated that with the increase of molecular weight of PAHs,PAHs in the water column were more easily attached to the particle phase,and the distribution of LMW-PAHs and MMW-PAHs monomers in the particle-dissolved phase of the water column was more balanced.The5-and 6-ring PAHs tended to be distributed more in the particulate matter.The seasonal variation of PAHs concentration in sediment of Dianshan Lake was dry season>normal season>wet season,and the component characteristics were not consistent with the two phases of the water column.The sediment was dominated by MMW-PAHs,and the percentage of HMW-PAHs increased significantly,indicating that the sediment was a sink for HMW-PAHs.The concentration of PAHs was highest in the maximum water depth in both wet and dry seasons,while it was highest in the surface water in normal season.The concentration of PAHs in sediment pore water was significantly greater than that of PAHs in the overlying water,and the fraction of LMW-PAHs in the dissolved phase decreased and that of MMW-PAHs increased with the increase of water depth.PCA principal component analysis was used to find that the particulate phase PAHs were mainly influenced by p H,chlorophyll a（Chl a）and dissolved oxygen（DO）.These environmental physicochemical parameters were significantly correlated with the mean concentration of particulate phase PAHs.（2）A quantitative water-air-sediment interaction（QWASI）model was used to systematically study the cross-interfacial transport（CIT）of PAHs in shallow lakes between adjacent media phases.The comparison between simulated and measured values shows that the model can better simulate the interfacial migration of PAHs in shallow lakes.The linear regression slope of air-particle partitioning in the Dianshan Lake region,m_r=-0.804,indicates that the air-particle partitioning has not yet reached a steady state,and there is a mixture of liquid absorption and surface adsorption of suspended particulate matter in the gas phase,and the expansion of pollution sources into the region tends to weaken.The simulation results found that atmospheric emissions and advective inputs were the main sources of PAHs in the lake,and part of their net loss（NL_A）was converted into total interfacial transfer flux（CIT）,and the conversion degree of HMW-PAHs was higher than that of LMW-PAHs.Fugacity fraction（ff）of 16 PAHs ranged from 0.04-0.86,and LMW-PAHs were released from the sediment to the upper water column,and the mean values of both MMW and HMW-PAHs ranged from 0.2 to 0.8,indicating that the interphase partitioning of MMW and HMW-PAHs was in a relative equilibrium.Among the various interfacial transport fluxes,sub-sedimentation transport is the dominant process for most PAHs.The composition of PAHs in the organisms and in the environmental media showed some similarity.The higher resuspension flux of HMW-PAHs may be related to the frequent hydrodynamic perturbations.（3）The concentration of PAHs in 19 species of aquatic organisms in Dianshan Lake ranged from 115.18 to 1136.04 ng/g dw,and the mean distribution of their interspecies concentrations was shellfish>shrimp and crab>fish,with MMW-PAHs and HMW-PAHs dominating in shellfish and LMW-PAHs in fish,shrimp and crab.The size of PAHs concentration in shellfish tissues was in the following order:coat membrane>visceral mass>gill>closed-shell muscle.The mean values of PAHs concentrations in five tissues of fish were in the following order:liver>intestine>gill>skin>muscle.（4）The PAHs content in the muscles of aquatic organisms showed a significant positive correlation with lipid content and a certain degree of negative correlation with organism length,and the concentration of lipid homogenized PAHs showed a significant negative correlation with log K_OW.The bioconcentration factors（BAFs）of six organisms ranged from 272-960,and the bio-sedimentation accumulation factors（BSAFs）ranged from 0.14-7.20.The trophic level amplification factor（TMF）values of all 16 PAHs monotypes were less than 1,indicating that PAHs experienced trophic level dilution in the aquatic food web of Dianshan Lake,and the concentration of PAHs in the immortal organisms gradually decreased with increasing trophic level,and the trophic dilution of PAHs was attributed to the biotransformation ability of aquatic animals to PAHs.（5）Positive Matrix Factor model（PMF）is used to quantitatively analyze the sources of PAHs in SPM,sediment and fish in Dianshan Lake,and the results show that PAHs in sediment and SPM mainly come from traffic exhaust emissions（including gasoline and diesel）,accounting for 43.3%-47.7%,followed by coking and petroleum volatilization leaks.Coal combustion sources in wet and normal seasons have a certain share;and PAHs in fishes were mainly from coking,coal combustion and gasoline tail gas emissions,with seasonal differences.Lifetime carcinogenic risk（ILCR）was used to assess the health risk of PAHs in air and water phases in Dianshan Lake,and the results showed that the ILCRs of PM_2.5was ranked as dry season>normal season>wet season,and the ILCRs by skin contact>swallowing>breathing,with potential health risk.The ILCRs of PAHs in water bodies is dry season>normal season>wet season,and the health risk of children is the highest and should be taken seriously.The health risk evaluation showed that the maximum allowable intake CR_U of PAHs bioeffectiveness in 12 fish species in Dianshan Lake ranged from 74.23 to 669.32 g/d,and the CR_U values of all fish species were greater than the daily per capita fish intake of urban residents of 62.3 g/d,indicating that consumption of all 12 fish species did not produce carcinogenic risk of PAHs,but the concentration of PAHs in Neosalanx tangkahkeii taihuensis Chen was higher and should be considered carefully.The consumption amount needs to be considered carefully.The concentration of PAHs in the surface sediment of Dianshan Lake is lower than the low ecological effect value,and the ecological risk is low.