In Vitro Digestion/Caco-2 Cell Model To Estimate Heavy Metal Bioaccessibility/Bioavailability In Site Soils And Its Toxic Effects On Human Health

Human health risk assessment is a key mean for the goverance of heavy metal contaminated site soils.The oral ingestion of soil was an important path for heavy metal exposure to human.During calculated the human health risk,the replacement of total concentration of metal elements with the bioaccessibility and bioavailability as assessment factor can overcome the defect of human health risk overestimation.There were several methods for bioaccessibilty assays,but the results among different methods were varied.There were scare studies of the bioavailability of heavy metal in the soils.In this study,four in vitro digestion methods including PBET,DIN,IVG and UBM were used to investigate and compare the bioaccessibilities of Co,Ni,Cu,Zn,As,Cd and Pb in different site soils.And the combination of IVG and Caco-2 cell model were further used for the study of soil As and Pb bioavailabilty.Then human health risk assessment based on total concentration?default value?,bioaccessibility and bioavailbility were compared.This study provided scientific supporting for the human health risk assessment and governance of heavy metal contaminated site soils.The main conclusions were as follows:The bioaccissibity of heavy metals in soil varies much between in vitro digestion methods and different digestion phases.bioaccessibility of Co,Ni,Cu,Zn,As,Cd and Pb were 0⁴5.71%,6.69¹29.78%,14.79¹22.62%,1.47¹28.75%,4.17⁶1.14%,8.48¹18.44%,0.02⁸3.94%,respectively.In gastric phase,the bioaccessibility of Co,Ni,Cu,As and Pb in IVG and UBM methods were higher than PBET and DIN methods.The bioaccessibility of Zn in DIN method was higher than those in other methods.The bioaccessibility of Cd in DIN and UBM methods were higher than PBET and IVG methods.In gastrointestinal phase,the bioaccessibility of Co in UBM method was highest.The bioaccessibility of Ni was high in UBM method and low in IVG method.The bioaccessibility of Cu in DIN and UBM methods were higher than PBET and IVG methods.The order of Zn bioaccessibility was DIN>PBET>IVG>UBM.The order of Pb bioaccessibility was PBET>DIN>IVG>UBM.Compared to the bioaccessiblity in the gastric phase,the bioaccessibility of Co in the gastrointestinal phase was decreased in DIN,IVG and UBM methods but increased for some soils tested in PBET method.The bioaccessibility of Ni,Zn,Cd and Pb decreased in all test methods.The bioaccessibility of As decreased in DIN and UBM methods and increased for some soils tested in PBET and IVG methods.The bioaccessibility of Cu decreased in PBET,IVG,UBM methods and increased in DIN method.Caco-2 cell model was well established,and then the combination of Caco-2 cell model with IVG method was further used to investigate the bioavailability of metal elements in the soils.The bioavailability of As and Pb was 1.77⁹.17%and0.39².68%,respectively.The bioavailable concentration of As and Pb was0.47².31mg·kg^-1 and 0.54⁷69.92 mg·kg^-1.Even bioavailability of Pb was low,the bioavailable concentration in some soils was up to 769.92 mg·kg^-1,which was higher than B sandard of standard of soil quality assessment for exhibition sites.Hazard quotient index and carcinogenic risk index of heavy metals based on total concentration were higher than that based on bioaccessibility or bioavailbility.Hazard quotient index based on the total amount of Co?Ni?Cu?Zn?As?Cd was higher than 1,but hazard quotient index based on bioavailability or bioavailability was less than 1 When hazard quotient index of one heavy metal was less than 1,the sum hazard quotient index of several heavy metals may higher than 1.Combined contamination in site soil should be paied attention to.Compared to default value of ALM or IEUBM model,blood lead concentration in adult or child and lead poisoning probability based on Pb bioaccessibility or bioavailability decreased.While calculated the risk control value for soil Co,Ni,Cu,Zn,As and Cd,the risk control value based on the bioavailability were higher than those based on the total concentration or bioaccessibility,and the risk control value based on total concentration was lowest.In ALM model,Pb risk control value based on bioavailability was 1.14 to 2.71 times of that based on bioaccessibilty and 4.47 to30.75 times of that based on Pb total concentration.In IEUBK model,Pb risk control value based on bioavailability was 1.01 to 1.06 times of that based on bioaccessibilty and 1.96 to 2.13 times of that based on Pb total concentration.Taking risk control value based on total concentration?default value?as soil restoration target value might overestimate health risk and increased repair cost.