Vertical Distribution And Migration Experimental Study Of PCBs In Soil In Yellow River Irrigation District Of Inner Mongolia

The Yellow River is the largest source of water supply in northern China,which undertakes the task of irrigating cultivated land in the Yellow River irrigation area.The development of irrigation area has greatly promoted the development of the country’s agricultural economy.Soil pollution in the Yellow River irrigation area is bound to have a certain degree of impact on regional food security and the coordinated development of the economy.Among them,polychlorinated biphenyls（PCBs）pollution is a problem that can’t be ignored To explore the pollution characteristics,vertical distribution and migration of PCBs in soils in the Yellow River Irrigation District.In this study the main agricultural production areas in the Yellow River Irrigation District of Inner Mongolia—Hetao Irrigation Area（Jiefangzha Irrigation Area,Ulanbuhe Irrigation Area）and Tumochuan Irrigation Area（Madihao Irrigation Area,Dengkou Irrigation Area,National Unity Irrigation Area）are selected as the study area.100 samples of farming profile soil（0～100 cm）were collected.Selected PCBs monomers detected in the Inner Mongolia section of the Yellow River as the maily research object to carry out research on the pollution characteristics and vertical distribution,and principal component analysis and cluster analysis were used to explore the pollution sources of soil PCBs,the USEPA health risk assessment model was used to assess the carcinogenic and non-carcinogenic risks of soil PCBs.And simulated the migration process of PCBs in the soil after irrigation through the soil column leaching experiment,and preliminarily discussed the influence of organic matter content and leaching amount on the migration of PCBs in the soil.The solute transport model was used to fit the experimental data of the soil column to fitting the retarding factors and dispersion coefficients of PCBs.They are used to characterize the influence of organic matter content and leaching amount on the migration ability of PCBs in the soil.The main research conclusions are as follows:（1）The detection rate rangesof PCBs monomers in soil in Yellow River irrigation area of Inner Mongolia from 35%to 100%,and the concentration range was ND～120.65ng·g^-1,with an average of 95.90 ng·g^-1.PCBs in soil are mainly low-chlorinated biphenyls,and the composition of PCBs monomers is similar to that in the water body of Inner Mongolia section of the Yellow River.The vertical distribution of PCBs in soil was high-low-high,the highest value was concentrated in 20～40 cm soil layer,and the lowest value was concentrated in 40～60 cm soil layer.The distribution of PCBs in the study area was dominated by low-chlorinated biphenyl content.Compared with low-chlorinated biphenyls,high-chlorinated biphenyls are more difficult to migrate to deep soil layers.The spatial distribution of irrigation areas from west to east shows a trend of high in the west and low in the east.（2）The effects of crop types and organic matter content on the vertical distribution and migration ability of PCBs in soil were investigated.The soil in the irrigation area was divided into soil of food crop,soil of fruit and vegetable and soil of oil crop according to the types of crops.PCBs content was the highest in soil of oil crop and the lowest in soil of fruit and vegetable.The change trend of PCBs in the soil of the three crop types at 0～60 cm soil layer was first increased and then decreased,the deep soil was different.The migration ability of low-chlorinated biphenyls in different crop types was similar to that of∑₈PCBs,while that of high-chlorinated biphenyls was different.The organic matter content in the soil gradually decreased with the deepening of soil layer.In the middle and upper soil layers,the PCBs concentration in the soil was higher with high organic matter content,and the PCBs distribution was disturbed in the deep soil.The organic matter content had a significant impact on PCBs migration ability.The higher the soil organic matter content was,the weaker the PCBs migration ability was.Compared with other irrigation areas in China and abroad,the PCBs pollution in Yellow River irrigation district of Inner Mongolia is high relatively,and the pollution in Ulanbu irrigation areas is most serious.（3）According to principal component analysis,the shallow soil PCBs in the study area may originate from the volatilization of paint additives,the use of electrical equipment residues,industrial production,and the incineration process.The soils in the Hetao Irrigation area,paint volatilization and residual sources contributed the highest rate of 81.34%;in the soil of the Tumochuan Irrigation area,the mixed sources of power equipment production and use and industrial thermal processes were the main sources,and the contribution rate was as high as 95.99%.The deep soil PCBs mainly originate from the migration of shallow soil PCBs.The main sources of soil PCBs pollution are atmospheric deposition,irrigation leaching,and microbial action.The cluster analysis results show that the possible sources of PCBs are Aroclor 1242,Aroclor 1248,Aroclor 1016,Aroclor 1232 and Aroclor 1221products and domestic transformer oil.Soil pose a carcinogenic risk to children.Oral ingestion is the main route of exposure,and adults are basically not exposed to health hazards.The oil crops Soil have the highest health risks,followed by food and fruits and vegetables have the least.（4）The results of soil column leaching experiment showed that the migration speed of PCBs in soil column was slow,the migration distance of PCBs was concentrated within5 cm,and the 0～2 cm soil layer concentrated more than 35%～60%of the total migration of PCBs.The higher the soil organic matter content,the stronger the retardation to PCBs migration,the slower the migration rate of PCBs.The greater the leaching amount,the greater the migration of PCBs in the upper soil,but the PCBs concentration in the deep soil did not change significantly.The experimental data fitting results showed that when the leaching amount is the same,the higher the organic matter content,the larger the retardation factor,the weaker the migration ability of PCBs;When the organic matter content is the same,the greater the leaching amount is,the greater the dispersion coefficient is,the stronger the migration ability of PCBs.