Spatiotemporal Variation Characteristics And Risk Assessment Of Heavy Metals In PM_2.5,TSP,and Sediments In Smelting Cities

A city in North China is a typical metal smelting city.The pollution degree of heavy metals in atmospheric particulate matters,dry and wet deposition and soil,as well as the health risk to the human body,are issues of general concern to the local public.In order to effectively control the local air and soil pollution.From January 2017to December 2019,the temporal and spatial variation characteristics and health risks of typical heavy metals in PM_2.5,TSP,and atmospheric deposition in local industrial,suburban,and mountain areas were analyzed.The potential pollution sources were analyzed.The effects of atmospheric deposition on the accumulation of Pb,As and Cd in soil were discussed.The main results are as follows:（1）From 2017 to 2019,the annual average mass concentrations of PM_2.5 and TSP in the industrial area first increased and then decreased.The average annual mass concentration of PM_2.5 was stable at 100μg/m³.The average annual concentration of TSP was 193μg/m³.The annual average concentrations of PM_2.5 and TSP in suburban and mountain areas increased year by year.The annual average concentrations of PM_2.5and TSP in the suburban area increased from 73.4 and 126μg/m³（2017）to 103 and 189μg/m³（2019）.The annual average concentrations of PM_2.5 and TSP in the mountain area increased from 82.1 and 150μg/m³（2017）to 93.0 and 182μg/m³（2019）.The concentrations of PM_2.5 and TSP in the three functional areas showed the seasonal variation characteristics of winter>spring>autumn>summer.Compared with the standard limit of annual average secondary concentration（GB 3095-2012）,the annual average mass concentration of PM_2.5 in the three functional areas exceeded the standard.Meteorological factors such as relative humidity,air temperature,wind speed,and air pressure significantly affect the mass concentration of PM_2.5.Traj Stat software analysis shows that the large-scale smelting enterprises in the city are located in the main contribution source area and pollution transmission direction of PM_2.5 in each functional area.Attention should be paid to the pollution of PM_2.5 by large-scale smelting enterprises in the region.（2）The annual average mass concentration of Pb,As and Cd in PM_2.5 and TSP in industrial,suburban,and mountain areas decreased year by year from 2017 to 2019.The annual deposition flux of Pb,As and Cd is consistent with the changing trend.In2017,the concentrations of Pb,As and Cd in PM_2.5 of the three types of functional areas showed a seasonal variation characteristic of high in autumn and low in summer.The results showed that the concentrations of Pb,As and Cd in TSP were higher in autumn and lower in summer in suburban areas,but not in industrial areas,with the highest values in autumn in mountainous areas.The concentrations of Pb,As and Cd in TSP were higher in autumn and lower in summer.The highest value appears in the mountain area in autumn.The deposition fluxes of Pb and As in the three functional areas were higher in summer.The contribution of wet deposition to Pb and As deposition fluxes is dominant in the total dry and wet deposition fluxes.The seasonal variation characteristics of Cd deposition flux in the atmosphere have spatial differences.（3）The concentrations of Pb,As,Cd in PM_2.5 and TSP and the deposition fluxes of Pb,As,Cd in the three functional areas from high to low were:industrial area>suburban area>mountain area.The main sources of Pb,As and Cd in atmospheric particulate matter and atmospheric deposition are smelter flue gas.The ratio of Pb,As and Cd in PM_2.5 to TSP was more than 50%.Pb,As and Cd in TSP were mainly distributed in PM_2.5.Traj Stat software analyzed the sources of heavy metals in PM_2.5,and the results showed that we should pay attention to the regional transport pollution within 350 km in the northwest,200 km in the East,and 200 km in the south of the study area.（4）The results of geoaccumulation index showed that the order of heavy metal pollution degree in PM_2.5,TSP,and atmospheric deposition from high to low is Cd>Pb>As.The comprehensive evaluation results of the single-factor index and the Nemerow index method showed that the evaluation results were consistent with those of geoaccumulation index,and Cd in atmospheric particulate matter polluted the soil most seriously through atmospheric deposition.The monitoring data of total Pb,As and Cd in clean soil（passenger soil method）of industrial zone from 2016 to 2020 are analyzed.It is found that the clean soil without heavy metal pollution is affected by atmospheric settlement in the industrial zone for two years,and the Cd content（0.94mg/kg）in the soil exceeds the soil risk screening value.Cd in the atmospheric deposition is harmful to soil seriously,which should be paid more attention to.The health risk assessment model proposed by EPA was used for calculation.The results showed that As and Cd in PM_2.5,TSP,and atmospheric deposition had certain carcinogenic health risks to children and adults.