Study On Spatial Distribution Characteristics And Risk Assessment Of PCBs In Topsoil Of Hetao Irrigation Area

Polychlorinated biphenyls（PCBs）have been widely used in industrial fields due to their special physical and chemical properties.The harm of PCBs to the ecological environment has also attracted increasing attention around the world.Hetao Irrigation District is an important commodity grain and oil base in northern China.It is the main and high-quality production area of spring wheat in China.There are many kinds of crops in the irrigation area,the irrigation system is perfect,and the agricultural production is developed.This study selects Hetao Irrigation District of Inner Mongolia as the study area,collects 243 surface soil samples,and analyzes the residual status and distribution characteristics of PCBs with different chlorine contents in soil,discuss the influencing factors of distribution characteristics under different conditions.This study explores the source of PCBs of the irrigation area through cluster analysis,and evaluates the health risks in order to provide a reasonable basis for the treatment of soil pollution of the irrigation area of the Yellow River Basin and even the national irrigation area.The main conclusions are as follows:1.The concentration range ofΣ₈PCBs in the soil of Hetao Irrigation District is 2.05～278.22 ng·g^-1;the average residual concentration is 43.12 ng·g^-1,of which the average concentration of low chlorinated PCBs（monochlorinated biphenyl to tetrachlorobiphenyl）is 35.89 ng·g^-1,accounting for 83.23%,which is the dominant component.The average concentration of high chlorinated PCBs（pentachlorobiphenyl to octachlorobiphenyl）is 7.23ng·g^-1,accounting for 16.77%,and the eight PCBs homologues are strongly variable.The pollution is in the middle level,among which the Urat Irrigation District is the most serious,followed by the Ulan Buhe Irrigation District.The distribution characteristics of low chlorination,high chlorination andΣ₈PCBs are similar,that is,the east and west are high and the middle is low.2.Among the factors affecting the distribution,the physical and chemical properties of soil（organic matter content,clay content and p H）are the main factors.The three physical and chemical properties have significant correlation with PCBs,and the distribution characteristics have spatial correlation with PCBs,which has the greatest impact on the distribution.Idle land in different land use types and food crops and agricultural and sideline products in different crops have a certain impact on the distribution of PCBs,which belongs to secondary factors.The planting of fruits has little impact on the distribution of PCBs due to its small quantity and concentrated distribution.The effect of irrigation mode from the Yellow River on the concentration of PCBs is greater than well irrigation,but they have no effect on the distribution of PCBs.3.According to the cluster analysis,monochlorinated biphenyl（PCB1）may originate from Aroclor1232 and degradation of PCBs with higher chlorinated.Trichloro biphenyl（PCB29）may originate from the leakage of capacitor impregnant,and high-chlorinated PCBs may originate from Aroclor1254,KC300,KC400 and KC500 industrial products.In addition,the industrial production activities of industrial parks in the irrigation area,the accumulation and burial of PCBs-containing waste,and even the by-products of combustion of coal and fuelwood,together with the effects of sewage discharge in the upstream area and atmospheric dry and wet deposition,all provide many sources for soil PCBs pollution in the irrigation area.4.Calculated according to the health risk assessment method recommended by the US Environmental Protection Agency（USEPA）:The contribution rates of carcinogenic risk and non-carcinogenic risk for both children and adults are:oral intake>skin contact>respiratory intake.Oral intake is the main way of carcinogenic risk,and the cumulative non-carcinogenic risk of children is greater than that of adults.Both carcinogenic and non-carcinogenic risks are within acceptable limits,and PCBs in the soil of Hetao Irrigation District will not cause adverse effects on human health.