Potential Sources Of Farmland Soil Pollutants And Residents Exposure To Pollutants In An Industrialized Town,Northwest China

In this study,Gaolan County,a newly developed industrial town in northwestern arid region in response to the development strategy of rural revitalization,was selected as the research area,and three types of pollutants in the local soil environment:PCBs,heavy metals and soil water-soluble ions were detected and analyzed.The concentrations of 18 kinds of polychlorinated biphenyls（PCBs）in farmland soil in Gaolan County were determined by gas chromatography-mass spectrometry.The concentrations of six heavy metals in farmland soil were determined by X-ray fluorescence spectrometry with wavelength dispersion method.The concentrations of eight water-soluble ions K⁺,Na⁺,Ca²⁺,Mg²⁺,NH₄⁺,Cl^-,NO₃^-and SO₄^2-in soil were determined by ion chromatography.The pollution sources,residents exposure and health and ecological risks of PCBs,heavy metals and water-soluble ions in the study area were explored and evaluated by using principal component analysis,multiple linear regression analysis and exposure model.The concentration of soil PCBs in the study area ranged from 3.675 to 19.146ng/g.The soil pollution degree of farmland near the industrial park was relatively high,followed by the urban-rural integration area,and the soil pollution degree at the urban-rural integration boundary was relatively low.Tetrachlorobenzene and pentachlorobenzene occupy higher mass fraction in∑₁₈PCBs.The PCBs in the soil may mainly come from the pollution sources related to the recycling and disposal of electrical equipment containing PCBs or the disassembly process,the thermal process sources generated by household coal combustion and industrial production enterprises,and the combustion related pollution sources.The combustion and industrial thermal process sources may make a greater contribution to the PCBs pollution in the study area.The concentrations of 6 heavy metals in the soil of the study area ranged from7.50 to 268.70 mg/kg.The average heavy metal pollution degree of farmland in the urban-rural integration area was relatively high,followed by industrial parks,and was relatively low at the urban-rural integration boundary.All six kinds of heavy metal elements were detected in the soil,the contents of Cr and Zn were higher in each sampling area,and the contents of As were lower.Soil heavy metal pollution is mainly attributed to the source of soil parent material and pollution emissions from traffic and industrial activities.The average concentrations of 8 kinds of water-soluble ions in soil samples in each sampling area ranged from 5.182 to 25.997 mg/kg.The highest concentrations were found in industrial parks,followed by the concentrations in urban and rural areas.The lowest concentration of water-soluble ions was observed at the urban-rural boundary.The composition of eight water-soluble ions in soil is Ca²⁺>K⁺>Mg²⁺>NO₃^->Na⁺>SO₄^2->Cl^->NH₄⁺.The pollution sources of traffic emission and industrial activities contributed the most to the heavy metal pollution of soil in the study area,followed by the source of soil parent material.The results of the potential health risk assessment of soil PCBs and heavy metals in the study area showed that the average daily exposure dose of adults and children was higher than the lifetime average daily exposure dose.From the perspective of different exposure groups,the exposure dose of pollutants through skin contact,oral and nasal breathing and oral ingestion of adults is lower than that of children,because the body weight of adults is much higher than that of children.From the perspective of different ways of exposure to pollutants,the oral ingestion of all kinds of people in the study area had a higher exposure dose to the three pollutants.The carcinogenic risk caused by exposure to PCBs and heavy metals in various populations in the study area is low,and the non-carcinogenic risk is at an acceptable level（10-6）.However,the carcinogenic risk of children is higher than that of adults.In addition,traffic emission and industrial thermal process,as possible major sources of pollutants in the study area,may bring adverse effects on long-term residents in the local population,which should be paid attention to.After the ecological risk assessment of PCBs and heavy metals respectively,the results showed that the 7 indicator PCBs in the study area basically did not contain toxicity,but the ecological risk brought by PCBs should be paid attention to.By calculating the potential ecological risks of heavy metals,it is concluded that the six heavy metals that this study focuses on belong to heavy to extremely heavy pollution.