Residues And Soil-air Exchange Of Chlorinated POPs With Their Associated Human Health Risks From Typical Agricultural Area And Industrial Area In The Hangzhou City

Persistent organic pollutants(POPs)have the characteristics of environmental persistence,semi-volatility,high toxicity and bio-accumulation.Therefore,POPs are of great concern around the world.Hexachlorocyclohexanes(HCHs),dichlorodiphenyltrichloroethanes(DDTs)and polychlorinated biphenyls(PCBs)are typical persistent chlorinated organic compounds.They were extensively producted and applied in China.Although their application have been banned for several decades,they can still be detected in the environment and continuously have adverse impact on ecosystem and human health.Hence,it is significant to conduct studies on their residual status,environmental fate and associated health risks.In this study,we collected soil and air samples in typical agricultural area(AA)and industrial area(IA)from the Hangzhou City.The concentrations of HCHs,DDTs and PCBs,and the enantiomeric fractions(EFs)of chiral a-HCH,o,p'-DDD and o,p'-DDT were determined.We aimed to evaluate the spatial and seasonal variation,air-soil exchange characteristics and associated health risks of these chlorinated pollutants.The major results are as follows.(1)In winter,the concentrations of?HCHs in soils from the study area were higher than those in summer,while the concentrations in soils from AA were higher than those from IA.The concrete concentrations were as follows:0.224-3.71(mean = 1.47)ng/g from AA in winter,0.228-1.61(mean = 0.555)ng/g from IA in winter,0.023-2.36(mean = 0.615)ng/g from AA in summer and 0.037-1.58(mean = 0.301)ng/g from IA in summer.In most soil samples,?-HCH was dominant among the four isomers.On the contrary,in winter,the concentrations of?HCHs in air from the study areas were lower than those in summer,while the concentrations in soils from AA were lower than those from IA.The concrete concentrations were as follows:20.1-42.0(mean = 27.9)pg/m~3 from AA in winter,26.8-77.1(mean = 42.7)pg/m~3 from IA in winter,32.4-73.0(mean = 40.8)pg/m~3 from AA in summer and 9.04-62.2(mean = 45.6)pg/m~3 from IA in summer.In most atmospheric samples,a-HCH was dominant.Source identification indicated that residues of HCHs in soils and air from the study area were mainly from past usage of technical HCHs.Enantiomeric analysis showed a preferential degradation of(-)-a-HCH in soils.In air,a preferential degradation of(+)-a-HCH in winter and a preferential degradation of(-)-a-HCH in summer were observed.Fugacity fractions(ffs)of HCHs suggested net volatilization from soil to air and soil was the secondary source for HCHs.In winter and in AA,ff values of HCHs were higher,indicating a stronger tendency of volatilization.Human health risks via various exposure pathways to HCHs in soils and air were further estimated.The results showed an absence of noncarcinogenic risks and very low carcinogenic risks of HCHs in both soils and air to human health.(2)In winter,the concentrations of?DDTs in soils from the study area were higher than those in summer,while the concentrations in soils from AA were higher than those from IA.The concrete concentrations were as follows:0.721-1594(mean = 96.5)ng/g from AA in winter,0.608-79.8(mean = 12.3)ng/g from IA in winter,0.312-938(mean = 67.5)ng/g from AA in summer and 0.572-125(mean = 12.1)ng/g from IA in summer.In most soil samples,p,p'-DDE and p,p'-DDT were dominant among DDTs and their metabolites.In winter,the concentrations of?DDTs in air from the study areas were lower than those in summer,while the concentrations didn't show any significance in spatial distribution.The concrete concentrations were as follows:37.1-363(mean = 52.1)pg/m~3 from AA in winter,48.5-141(mean = 42.5)pg/m~3 from IA in winter,90.7-325 pg/m~3(mean = 137)from AA in summer and 33.5-401(mean =162)pg/m~3 from IA in summer.Source identification indicated that residues of DDTs in soils likely originated from the historical usage and new input of DDTs and dicofol.In most atmospheric samples,DDT residues were impacted by the new input of dicofol.Enantiomeric analysis showed both o,p '-DDD and o,p'-DDT were non-racemic in all soil and air samples.For o.p'-DDT,a preferential degradation of(+)-enantiomer was observed in both soil and air samples.For o,p '-DDD,a preferential degradation of(+)-enantiomer in soil and a preferential degradation of(-)-enantiomer in air were observed.Fugacity fractions(ffs)of DDTs suggested three status for DDTs,i.e.volatilization,deposition and equilibrium.In winter and in AA,ff values of DDTs were higher.Human health risks via various exposure pathways to DDTs in soils and air were further estimated.The results showed an absence of noncarcinogenic risks and very low carcinogenic risks of DDTs in both soils and air to human health.(3)In winter,the concentrations of?PCBs in soils from the study area were higher than those in summer,while the concentrations didn't show any significant differences in spatial distribution.The concrete concentrations were as follows:68.6-1828(mean = 524)pg/g from AA in winter,104-1838(mean = 404)pg/g from IA in winter,47.4-1327(mean = 323)pg/g from AA in summer and 25.2-804(mean =307)pg/g from IA in summer.In most soil samples,5C1-and 6Cl-PCBs were dominant among PCB homologues.Be similar to soil samples,in winter,the concentrations of?PCBs in air from the study area were higher than those in summer,while the concentrations didn't show any significant differences in spatial distribution.The concrete concentrations were as follows:224-480 pg/m~3(mean = 345)from AA in winter,233-537(mean = 326)pg/m~3 from IA in winter,135-553(mean = 353)pg/m~3 from AA in summer and 39.6-253(mean = 133)pg/m~3 from IA in summer.In most atmospheric samples,7Cl-PCBs were dominant.Source identification indicated that residues of PCBs in soil samples likely originated from commercial Aroclor 1254,while PCBs in air may be from several kinds of commercial Aroclor.Fugacity fractions(ffs)of PCBs suggested an equilibrium condition or deposition of PCBs from air to soil.Fugacity fractions of PCBs were associated with their molecular weights.Ff values of PCBs in winter were higher than those in summer.The spatial variabilities of ff values were associated with molecular weights of different PCB congeners.Human health risks via various exposure pathways to PCBs in soils and air were further estimated.In several soil samples,PCBs presented noncarcinogenic risks to children.In other soil and air samples,there were no noncarcinogenic risks to human health.In addition,low or very low carcinogenic risks of PCBs in soil and air to human health were observed.