Polycyclic Aromatic Hydrocarbons(PAHs) In Aquatic Environment Of Yinma River Basin:Spatial-temporal Distribution,Risk Assessment And Fate

Yinma River Basin located in the middle part of Jilin Province of China,is the major tributary of the Secondary Songhua River,and is also the primary water sources for domestic water supply and irrigation of farmlands in the region.However,with the rapid development of urbanization,industry and agriculture,the pollution from domestic and industrial wastewater,runoffs,oil foundation,vehicular exhausts and combustion of coal and agricultural wastes are increasing greatly,which possibly result in contamination of polycyclic aromatic hydrocarbons(PAHs)in aquatic environment,mainly including water and sediment.Accordingly,priority 16 PAHs recommended by the United States Environmental Protection Agency were selected to investigate.Based on methods of monitoring concentrations of PAHs in 17 monitoring sections,simulation experiments,numerical simulation,we investigated temporal-spatial distribution,evaluated ecological and human health risks,identified the primary sources,and explored the transport and transformation mechanisms and fate of PAHs in aquatic environment.The results for monitoring concentrations of 16 PAHs in water and sediment from 13 provincial monitoring sections and 4 state monitoring sections showed that,the highest average concentration of total PAHs was occurred in wet season,while the lowest was occurred in dry season;average concentration of total PAHs in sediment was the highest in wet season,but the seasonal variation was not great;the highest concentrations of total PAHs in water were found in Sihua Bridge of Changchun City located in upper reach of Yitong River,and upper reach of Yinma River;the highest concentration of total PAHs was found in YM1,which was almost one time higher than in other sampling sites;the proportions of low-ring PAHs in water and sediment were both the highest.Based on the results for field survey and the methods of molecular diagnostic ratios of isomeric PAHs,the primary sources of PAHs in aquatic environment of Yinma River Basin were identified as combustion of agricultural wastes,runoffs,domestic and industrial wastewater,household wastes,and emissions of vehicle and industry.This research applied simulation experiments to explore the transport and transformation processes of phenanthrene(Phe)and pyrene(Pyr)in air-water-sediment system,and the results indicated that sediment sorption and desorption,biodegradation in sediment and volatilization were the main processes;and the processes showed seasonal variations.Besides,we investigated the transport and transformation mechanisms of Phe and Pyr in aquatic environment.The kinetic process for Phe was similar with Pyr,sorption processes were mainly controlled by diffusion,the roles of chemical sorption were quite weak;but in desorption processes,besides diffusion,the chemical sorption also played an important role.The mechanisms for biodegradation of Phe and Pyr by microorganisms from sediment of Yinma River Basin were investigated: firstly,highly-efficient bacteria were screened,Bacillus sp.6A-1 for Pyr and Klebsiella sp.EP2 e for Phe;secondly,metabolic pathways were respectively validated with transcriptome sequencing.Markov chain was employed to study the distribution and fate of Phe and Pyr in air-water-sediment system.The results indicated that in normal season,500 ng/mL of Phe in water was eliminated from water and sediment to a negligible level over 1000 h;in wet season,over 250 h,500 ng/mL of Phe in water was eliminated from water and sediment to a negligible level;in dry season,above 90% of Phe was eliminated from water,while 31% of Phe was still remained in the sediment.As for Pyr,in normal season,100 ng/mL of Pyr in water was eliminated from water to a negligible level over 150 h,and was eliminated from sediment to a negligible level over 250 h;in wet season,100 ng/mL of Pyr in water was eliminated from water to a negligible level over 50 h,while was eliminated from sediment to a negligible level over 120 h;in dry season,100 ng/mL of Pyr in water was eliminated from water to a negligible level over 550 h,but a small proportion of Pyr was still remained in the sediment over 600 h.This research was applied microcosm experiments and Pearson's correlation coefficients to testify efficiency and accuracy of application of Markov chain to predict distribution and fate of Phe and Pyr in aquatic environment.The fitting results suggested that the results for application of Markov chain were perfectly matched with the results for microcosm experiments;the results of Pearson's correlation coefficients indicated that the fitness of the results for application of Markov chain and results for microcosm experiments was quite high.It can be concluded that the accuracy and efficiency of application of Markov chain to predict distribution and fate of Phe and Pyr in aquatic environment were high.Species sensitivity distribution and hazard quotients were employed to evaluate ecological and human health risks of PAHs in aquatic environment,the results indicated that,the ecological risks of total PAHs in both water and sediment were high in upper and lower reaches of Yinma River and upper reach of Yitong River;the investigated PAHs in water of monitoring sections located in Wukai River and Ganwuhai River were existed higher carcinogenic risks;PAHs in water and sediment of Yinma River Basin were existed low non-carcinogenic risks.This research was provided effective information on pollution remediation and control of PAHs in aquatic environment of Yinma River Basin;and applied scientific data to define the environmental standards of PAHs in aquatic environment.Besides,this study provided scientific basis with application of Markov chain to predict fate of organic pollutants in multimedia environment.