Pollution Characteristics Of POPs In Soil And Human Exposure Risk Assessment In Typical Functional Areas Of Inner Mongolia

The development of economy and the progress of society not only bring people rich material enjoyment,but also lead to challenges to the ecological environment.Once there are serious problems in the environment on which human beings rely for survival,they will eat back the social achievements,cause harm and even cause disaster.Nowadays,the pursuit of"bluer sky,greener trees,clearer water and more beautiful city" has become the common aspiration of people.Persistent organic pollutants(POPs)can exist in the environment for a long time.Through volatilization,diffusion,migration,dry and wet deposition,they can realize the spatial and temporal distribution of pollutants and cause various environmental media pollution.Some POPs are carcinogenic,teratogenic,mutagenic and endocrine disrupting.With the accumulation and amplification of POPs in the food chain,POPs will eventually harm human health.Therefore,POPs have attracted more and more attention in the world.Located in the northern frontier,Inner Mongolia is an important ecological barrier in China,which is related to the ecological security of Northeast China,North China,Northwest China and even the whole China.The geographical location of high altitude,the unique diet culture,the lipophilic epidermis of soil in agricultural and grassland areas are easy to accumulate POPs.Its diversified industrial structure is conducive to the analysis of environmental behavior of POPs.Therefore,this study selected the industrial,agricultural and grassland areas of Inner Mongolia as the research area,through analyzing the pollution characteristics of four representative POPs,including polybrominated diphenylethers(PBDEs),polychlorinated biphenyls(PCBs),new halogenated flame retardant(NBFRs and DPs)in soil and bark of different functional areas,to explore the migration rules and possible sources,to clarify the long-distance migration ability of different POPs,and to evaluate human exposure risk,in order to provide data support for POPs pollution and prevention in ethnic areas of China and promote the sustainable development of ecological environment in Ethnic Areas.The major results were as follows.(1)The concentration range of ∑8 PBDEs in industrial soil was 1407.89-27466.17 pg·g-1,with an average of 17576.43 pg·g-1,which was 2-5 orders of magnitude lower than the domestic waste dismantling sites with high pollution of PBDEs,and slightly higher than the pollution level of Beijing,Shanghai and other domestic cities.The level of PBDEs in agricultural and grassland soils was roughly the same as that of European background soils and the Yangtze River Delta region,but about two order of magnitude higher than that of the Tibet Plateau.The total average level of bark was slightly lower than the average level of bark in China and the concentration level of bark in rural and urban areas of the United States.BDE209 was the most important congener in all samples.The average concentration of BDE209 in industrial soil was about 12 times higher than that in agricultural soil,and about 8 times higher than that in grassland soil.The main reason was that there were sources of Deca-BDEs in industrial areas.However,there was no significant difference in soil concentrations between agricultural and grassland areas.The sources of Deca-BDEs used in the two areas were less,and the possible pollution sources were similar.Except BDE209,high brominated BDE183 and BDE99 were the main pollutants in Baotou,while BDE28,BDE99 and BDE100 were the main pollutants in Hohhot.This was mainly affected by the degree of industrialization development of the two cities.As a new industrial area,Hohhot tends to be energy-saving and environmental protection enterprises with relatively low pollution.High brominated PBDEs,which have weak migration ability,were easy to be deposited in the soil around the high pollution sources.High brominated PBDEs may degrade in the process of migration,forming more easily migrated low brominated compounds,thus affecting agricultural and pastoral areas in a long distance.Low brominated BDE28 and BDE47,which have strong migration ability,were the main components of bark and atmosphere in industrial areas.The composition of PBDEs congeners in bark of agricultural areas was consistent with that in bark of industrial areas,which reflected that air pollution in industrial areas and agricultural areas had homology.PBDEs pollution in agricultural and pastoral areas mainly comes from exogenous air input.Health risk assessment found that the overall exposure risk of PBDEs to local residents was acceptable,but it can’t be ignored that the non-carcinogenic risk of BDE28 in agricultural and grassland areas has exceeded the impact of BDE209,and the non-carcinogenic risk of low brominated BDE28 and BDE47 in agricultural and grassland areas were even higher than that in industrial areas(2)The concentration range of ∑18PCBs in the soil of industrial,agricultural and grassland areas was 10.13-335.82 pg·g-1,and the average concentration was 65.77 pg·g-1,which was lower than that at home and abroad.The strong migration ability of PCB28 made the contribution rate of PCB28 to the total concentration of soil in non-industrial areas higher than that in industrial areas.The detection rate of low chlorinated PCB28 and PCB52 in each sample was 100%,which had become a ubiquitous pollutant in Inner Mongolia.The average pollution levels of high chlorinated PCBs(Penta-PCBs,Hexa-PCBs,Hepta-PCBs)in the soil of industrial areas were higher than that in agricultural and grassland areas,the main reason was the weak migration ability leads to more impact on the soil around the pollution sources in the industrial area.The total concentration of PCBs in the bark of industrial area was slightly higher than that of agricultural area,but there was no significant difference between in industrial area and agricultural area,which reflected the homology of PCBs in the air of Inner Mongolia.The results showed that the main pollution of DL-PCBs was in the soil environment medium.The 12 kinds of DL-PCBs in Baotou were the largest in the study area,with an average concentration of 26.28 pg·g-1,while the toxicity equivalent value in Hohhot was the highest(0.0616 pg WHO-TEQ·g-1).PCB118 in soil had the highest contribution rate to the total concentration of DL-PCBs,and was the main contributor to the toxic equivalent concentration of DL-PCBs in agricultural and pastoral areas.The pollution of PCBs in Inner Mongolia mainly comes from UP-PCBs produced by heat related industrial processes.The long-distance migration of low chlorinated PCBs affects remote pastoral areas.The non-carcinogenic exposure risk of children in grassland areas had exceeded that of adult males in industrial areas.It was necessary to strengthen the attention of UP-PCBs to children in remote areas.(3)The total concentration range of 6 NBFRs in the soil of industrial,agricultural and grassland areas was 1.06-981.51 pg·g-1,the average concentration was 132.07 pg·g-1,and the total concentration range of DPS was ND-352.53 pg·g-1,the average concentration was 58.59 Pg·g-1.which were in a lower pollution level compared with domestic and foreign.Different types of new halogenated flame retardant showed the trend of TBPH>PBBA>anti-DP>syn-DP>HBB>PBT>PBBz>PBEB.It was found that HBB is easy to degrade in the migration process,and,PBBA,TBPH and DPs have weak migration ability compared with PBBz and PBT,which makes them easier to be deposited around the pollution source.TBPH was the main pollutant in industrial areas,especially the point source pollution.Due to the strong migration ability of PBBz and PBT,the pollution level in agricultural and grassland areas was higher than that in industrial areas.The pollution did not come from industrial areas,but may be the remote source pollution of low altitude areas,which has become a common pollutant in Inner Mongolia Autonomous Region.fanti of DPs showed a trend of grassland areas>agricultural areas>industrial areas.DPs had a weak correlation with PBBA and TBPH,which might have a similar pollution source.The results showed that the daily exposure of NBFRs and DPs in Baotou was the largest.TBPH and PBBA with weak migration ability had greater health risk to the residents in the industrial areas,while PBT and PBBz with easy migration ability had greater impact on the health exposure risk of the residents in remote grassland areas.(4)The affinity of PBDEs and HSA was the result of the interaction of kinetic binding rate and dissociation rate.Except BDE209,the increase of the number of bromine atoms decreased the dissociation rate of the complex,which was beneficial to the interaction between PBDEs and HSA.In isomers,ortho bromine was more beneficial to the interaction between PBDEs and HSA than meta bromine due to the influence of the binding rate Molecular docking showed that the amino acid residues of eight PBDEs in the functional region around site I of HSA binding site were different,resulting in the differences of van der Waals force,hydrogen bond and electrostatic force between different types of PBDEs and HSA,which further affected the affinity.The kinetic process of interaction between DL-PCB and non-DL-PCB with HSA was obviously different,but the affinity showed the same rule,that is,the affinities between DL-PCB and HSA were greater than that of non-DL-PCB.The affinities of DL-PCBs(PCB77,105/118,169)and non-DL-PCBs(52,101,138,180)with HSA increased with the number of chlorine atoms.Molecular docking showed that the electrostatic force and π-π interaction of different amino acid residues were the total driving force of the interaction between PCBs and HSA.The results showed that BDE153,154 and 183 had relatively high affinity with HSA,while BDE28,47,100,209,PBBz and TBPH had relatively low affinity with HSACombined with the affinity value from POPs and HSA,and EPA risk assessment model,it was found that the total vivo exposure risk of four kinds of POPs in industrial areas was the highest(Ctr=20.20 ng·kg-1 bw),followed by agricultural areas(Ctr=2.82 ng·kg-1 bw),and pastoral areas was the lowest(Ctr=2.71 ng·kg-1 bw).Vivo exposure risk of BDE209 in Inner Mongolia was the highest.BDE183,154,153 and HSA had strong binding ability,which increased the risk of vivo exposure in the agricultural and grassland areas,while the weak combination ability of BDE28,47 and HSA reduces the risk of vivo exposure to the agricultural and grassland areas.Vivo exposure risk of UP-PCBs was the lowest.High chlorinated PCBs only had low vivo exposure in industrial areas,and had little impact in agricultural and grassland areas.Low chlorinated PCB28 was the congener with the greatest vivo exposure risk in industrial,agricultural and grassland areas.The impact of low brominated PCBs on remote areas cannot be ignored.At the same time,vivo exposure risk from NBFRs and DPs in agricultural and grassland areas was the same order of magnitude as that in industrial areas.The strong binding ability of PBBA,PBT and HSA increased the risk of internal exposure in vivo in industrial,agricultural and grassland areas,while the relatively weak binding ability of PBBz and HSA reduced the risk of vivo exposure in remote grassland areas.DPs in agricultural and grassland areas of Inner Mongolia had higher fanti than that in industrial areas.Affected by the interaction affinity with HSA,the vivo exposure risk of anti-DPs in agricultural and grassland areas was further increased.