Spatiotemporal Variation And Health Risk Of The Accumulation Of Polycyclic Aromatic Hydrocarbons In Urban Area Soils

Many experts and scholars at home and abroad are paying attention to the distribution of PAHs in the urban environment because many PAHs are carcinogenic and mutagenic.The soil,an important environmental medium in urban areas,is the most important sink for many contaminants.The amount of PAHs in the soil environment often accounts for much of the PAHs present in the urban ecological environment.Therefore,the study of PAHs in urban area soils is of great significance.Since previous researchers have paid more attention to the static problems of PAHs in urban area soils,such as their concentration,composition,sources,and so on,there has been less research concerning dynamic PAH accumulation.The multimedia fugacity model is one of the models widely used to simulate the environmental fate of organic pollutants.However,because of its homogeneous phase hypothesis and its assumption that the organic carbon content of environmental media is the most critical factor for the absorption of pollutants,use of these simulations could cause large errors for PAHs.In addition,simulation of the dynamic properties of organic pollutants requires relevant environmental parameters from the past.However,it is difficult to obtain these environmental parameters due to the passage of time.For the reasons stated above,this paper chooses Nanjing City as research region.Firstly,we study the distribution and sources of PAHs in urban area soils.We also summarize the factors governing the accumulation of PAHs in urban area soils and use a multiple linear regression model to derive a quantitative representation.Secondly,this paper attempts to utilize the multimedia urban model(MUM)to simulate the distribution and transport of PAHs in the current urban environment,which will provide critical parameters for the dynamic simulation of PAHs in the soil.Thirdly,we adopt this regression model,coupled with a multimedia fugacity Ⅳ level model,to simulate the process of historical PAH accumulation in urban area soils.The multimedia fugacity IV level model is combined with a scenario simulation method to predict the tendency PAHs of to accumulate in the soil.Fourthly,the characteristics of the spatial distribution and change processes are analyzed using the results of the simulation described above,and the current and future health risks of PAH pollution of the soil are assessed.Finally.we put forward some policy recommendations of environmenta]management based on the conclusions of this article.The main conclusions can be summarized as follows.(1)A gradient of contamination was evident from urban to rural areas in Nanjing.The mean total concentrations of Σ16Hs were 3330 ng g-1 for urban soils,1680 ng g-1 for suburban soils,and 1060 ng g-1 for rural soils.Among different functional areas,the higher level of PAHs content was found in the roadside,followed by greenbelt,parkland,commercial district and residential areas.The composition of soil PAHs was characterized by the high-molecular-weight PAHs.The old urban districts and commercial centers were the most contaminated of all areas in Nanjing.The distribution pattern of heavier PAHs was in accordance with 116PAHs,whereas the pattern of lighter PAHs showed some special characteristics.Traffic emissions,coal and biomass combustion are the main sources by ratio method and Positive Matrix Factorization.(2)The distribution of PAHs in urban area soils is affected by many factors,but there is no consistency in the key factors affecting PAHs with different ring systems.These factors can be divided into natural and human factors that include population density,road network density,urbanization history,distance from the center,soil organic carbon content soil black carbon content,and the granulometric composition of soil.However,there is no consistency in the key factors affecting PAHs with different ring systems mainly reflect in the 2-ring PAHs and other PAHs.A multiple linear regression model was constructed to integrate the natural and human factors associated with soil PAHs in urban areas,which provided a new method for the reconstruction of PAHs content in urban area soils.(3)The improved multimedia fogacity model,the key parameter-organic carbon is replaced by black carbon,could significantly improve simulation accuracy for low-molecular-weight PAHs.but it is not significant for high-molecular-weight PAHs.A grid-based multimedia fugacity model further reveals the spatical diversity of environmental processes for PAHs.The assumption that black carbon is the most critical factor for PAH adsorption by environmental media(BC-Model)provides better simulation results for low-molecular-weight PAHs.while the simulation results are not of great significance for high-molecular-weight PAHs,compared with the original model.A griding study area could overcome the limitation of multimedia fugacity model about environmental nedium homogenization and further reveal the spatical diversity of environmental processes for PAHs.(4)The multiple linear regression equation,coupled to the multimedia fugacity IV level model,could effectively reconstruct historical accumulative process of PAHs in urban soils.The multimedia fugacity IV level model,combines the scenario simulation method,could predict accumulative trend of PAHs in urban area soils.The multiple linear regression equation,coupled with the multimedia fugacity Ⅳ level model,was used to simulate the process of phenanthrene and benzo[a]pyrene accumulation resulting from Chinese economic reform(1978).The results of the simulation indicate that the concentrations of phenanthrene and benzo[a]pyrene are increasing rapidly,which shows that economic development significantly affects the accumulation of PAHs in urban area soils.The scenario simulation method,combined with the multimedia fugacity Ⅳ level model,was used to simulate the PAH content of soil in the future.The results indicate that the pollution level will decrease significantly if the amount of emissions and external sources are reduced by half.(5)An overall soil study exists concerning the current potential risk of cancer in children and adults from different routes of exposure.The carcinogenic risk of each exposure to the total contribution rate,arranged from larger to smaller,are as follows:skin contact>eating soil>respiratory intake.Current research shows that many soil PAH content values exceed the threshold of high-risk health risks.These sites need to be brought to the attention of relevant Departments.Assessing soil PAH content values in 2030 under different forecast scenarios indicate that decreased significantly only by controlling the emission and external sources of PAHs.