Distribution Characteristics And Risk Assessment Of PAHs In The Riparian Zone Of Shenyang Section Of Liaohe River Main Stream

The main stream of Liaohe River has become an ecological fragile zone in Liaoning Province,which not only threatens the ecological security of Liaohe River,but also restricts the sound and rapid development of regional economy and society.It is very important to realize the goal of ecological protection and restoration of the main stream of Liaohe River and restore the ecological land of the main stream of Liaohe River.In order to accurately grasp the status of soil organic pollution in the riparian zone of Liaohe River and provide an important basis for ecological protection and control of the main stream of Liaohe River,this study took Shenyang section of the main stream of Liaohe River as the research area,selected 16 priority controlled polycyclic aromatic hydrocarbons as the research object,analyzed the pollution characteristics of polycyclic aromatic hydrocarbons in the riparian zone of the main stream of Liaohe River and carried out ecological evaluation.Specific research results are as follows(1)Analysis of soil structure characteristics in the riparian zone of Shenyang section of Liaohe River.Through soil sampling in riparian zone,the lithological composition,particle size distribution and pore characteristics were analyzed to clarify the characteristics of soil structure in riparian zone.(2)Assessment of environmental quality in the riparian zone of Shenyang section of Liaohe River.Fuzzy comprehensive evaluation method and single factor method were used to evaluate the water quality of riparian wetlands.The results showed that the ammonia nitrogen content exceeded the standard 3 times at Hongmiaozi,the other sampling points all met the water quality standard of Class II.The dissolved oxygen,total suspended matter,biochemical oxygen demand and chemical oxygen demand were mostly between Class IV and V.Potential ecological risk index method was used to determine that Cu,Pb and Cr in sediments threatened the environmental level.(3)Distribution characteristics of polycyclic aromatic hydrocarbons(PAHs)in Shenyang section of Liaohe River.In order to study the distribution characteristics of polycyclic aromatic hydrocarbons(PAHs)in the riparian soils of Shenyang section of Liaohe River,11 sampling sites were set up in the study area and 16 PAHs were detected.Apart from acenapHthene,15 other priority PAHs were detected.The content of PAHs in the soil of Shenyang section of Liaohe River mainstream is 7.87～44.61ug/kg,with an average of 13.04ug/kg.PAHs are mainly composed of 3,4 and 5 rings,and the pollution of PAHs is at a low level.The ratio method,isomer ratio method and principal component analysis method were used to analyze the sources of PAHs in the soil of Shenyang section of Liaohe River.(4)The correlation analysis of polycyclic aromatic hydrocarbons(PAHs)in Shenyang section of Liaohe River.The Pearson correlation among pHenanthrene,fluorene,fluoranthene and pyrene is close to 1,that is,there is a good correlation among the four PAHs monomers;there is no correlation between PAHs and pH,TOC,NH3-N in the study area.The content of PAHs in soil was significantly correlated with the four elements of heavy metals such as Cr,Cu,Zn and Pb.The correlation among 16 PAHs was determined by R-type cluster analysis,and the Q-type cluster analysis was used to classify the PAHs.It provides technical basis for the future research and treatment of PAHs.(5)Laboratory experiments on migration and transformation of polycyclic aromatic hydrocarbons.Adsorption and desorption experiments were used for analysis.In the static adsorption experiment,the kinetic adsorption of pollutants by Riparian media in the study area satisfies the quasi-second-order adsorption model.Soil quality has an effect on the adsorption capacity.The adsorption capacity of clay to pollutants is better than that of sandy soil to pollutants.The adsorption capacity of PAHs was positively correlated with the number of rings and molecular weight of PAHs.Hengry adsorption thermodynamic model of PAHs in riparian zone of the study area was established.The desorption experiments show that the desorption kinetics of PAHs in the riparian zone satisfies the quasi-second-order kinetics model.The relationship between napHthalene desorption capacity of sandy soil and clay is sandy soil>clay.The analytical rate is inversely proportional to the specific surface area of the medium.The desorption rate of polycyclic aromatic hydrocarbons(PAHs)with different ring numbers in the pHase medium is clay>sandy soil.The desorption thermodynamics of napHthalene and pyrene by Hannandai in the study area conforms to Langmuir model.(6)Ecological risk assessment of polycyclic aromatic hydrocarbons(PAHs)in Shenyang section of Liaohe River.The ecological health risk assessment of riparian zone was carried out by three methods,i.e.hazard assessment,dose effect assessment and exposure assessment of polycyclic aromatic hydrocarbons(PAHs).The results of the evaluation are non-polluting.Biotoxicity risk assessment showed that the relative pollution coefficient RCF of Nap,Ace,Flo,BaA and DahA was less than 1,indicating that the potential hazard probability to organisms was very small.BbF and BkF are the most easily harmful PAHs monomer compounds in the soil of Liaohe riparian zone,but the probability of adverse effects on organisms is very small.Through 15 kinds of risk quotients,RQ_PAHs(NCs)is about 38.759,RQ_MPCs is about 0.392.From the level of ecological risk level,the riparian zone in the study area is at a low risk level.Seven cancerous PAHs were the main contributors to the toxicity equivalent of PAHs in soil.