PAHs Distribution Characteristics,Source Analysis And Risk Assessment In Farmland Soil Along Shanghai Traffic Line

As of December 2017,the number of family cars in China has exceeded 400million.With China’s economic growth,car ownership and per capita holdings will continue to grow.Pollutants such as polycyclic aromatic hydrocarbons（PAHs）,which are generated during incomplete combustion due to incomplete combustion,adhere to the particulate matter and are collected in the soil along the road by atmospheric transport,rain erosion,surface runoff,etc.Therefore,the traffic source has become the main source of environmental pollution along the road.At present,the research on farmland soil near traffic roads is concentrated in the surface soil near the road.However,under the action of wind,runoff,irrigation and biological disturbance,the road-dense PAHs will gradually spread into the soil along the road.In the system,the surface PAHs gradually infiltrated into the deep soil,affecting the absorption of the roots of the crops,and then enriching the human body through the action of the food chain harms its health.In this paper,the Shanghai road is divided into four road grades of national highway,expressway,urban trunk road and urban secondary trunk road,and 41 mixed samples of surface soil are collected on the road side of different road grade,and the cross-section is set on one side after the samples of G10,S2,S9,S12,T1,T2 and F3 are taken as examples.The surface soil mixture samples were collected at the distance of 0 m,5 m,10 m,20 m,40 m,60 m,80 m,120 m,200 m and 500m,respectively.The soil column sampler was used to take the rice field and the bean field soil column in the agricultural dense area and away from the G10 and T1 sample points of the Shanghai national control air pollution point source,and the water samples in the crops and surrounding water environment at different distances were collected.A synergistic analysis of PAHs in atmospheric particulate matter and farmland soil was carried out for T1 samples.The source analysis and ecological risk assessment of farmland soil systems along the road were carried out by using various PAHs source analysis and evaluation methods,in order to control the soil pollution of farmland in Shanghai.The environmental management policy provides a scientific basis.The main research results are as follows:（1）The content of PA16PAHs in 41 farmland soil samples on the side of Shanghai traffic trunk line ranged from 17.23-3774.90ng/g,with an average of353.77ng/g,which was lower than that of most other countries.After detecting 70samples of gradient samples,it was found that the content of∑₁₆PAHs in the soil decreased firstly and then decreased with the increase of the distance from the shelter forest.The concentration of PAHs in the soil column showed the depth of the soil.Increasing and decreasing trend.（2）The content of∑₁₆PAHs in G10 sample farmland crops was between209.80¹461.76ng/g,and the content of∑₁₆PAHs in T1 sample farmland crops was between 101.22¹63.09ng/g.The average content of∑₁₆PAHs was G10>T1.The content of PAHs in legumes is higher than that in rice.The tricyclic and tetracyclic PAHs in the water samples accounted for a large proportion,while the PAHs in the water samples were mainly in the middle and low rings,and the proportion of high-ring PAHs was less.（3）Based on the results of the PMF model,according to the average ratio of factor contribution rate,the main source of PAHs in the surface soil of Shanghai roads is traffic discharge,but the main sources of surface soils at different distances from the road are different,which are close to 0⁴0m.The soil of roads is greatly affected by traffic emissions,while the soils that are far away from roads（40⁵00m）account for a large proportion of coal and biomass combustion sources due to the influence of nearby households.The characteristic factor ratio method reveals that the PAHs in the soil of 0³0cm tillage layer are mainly derived from the mixed source of petroleum and coal combustion,while the deeper soil indicates the combustion source of coal and biomass.（4）The characteristic ratio method was used to analyze the crops along the traffic.The PAHs of some crops in the farmland of G10 and T1 were mainly from the burning of petroleum.The TOR method was used to detect the EC content of atmospheric particles in T1 samples,indicating that the EC/OC ratio of samples exceeding 63.5%is between 0.4 and 0.6,which reveals the effects of biomass and fossil fuel combustion;Char/Soot ratio is used.The law shows that coal combustion contributes significantly to atmospheric EC in the region.（5）Using the risk quotient method to evaluate the ecological risk of PAHs and∑₁₆PAHs in soil,use the lifetime cancer risk（ILCRs）model to evaluate the health risk of soil PAHs,and use the RQ-TEQ composite model to calculate the PAHs pollution index.The results showed that the RQ_（NCs）value of the farmland was mostly>1,and the RQ_（MPCs）value of each monomer was<1;the farmland soil along the national highway and the expressway had higher cancer risk,and the farmland next to the main and secondary trunk roads.The soil has potential carcinogenic risk;the pollution index（P）of 41 sample PAHs ranges from 0.001 to 1.71,of which 95.12%of the samples are at low ecological risk and basically safe.