| Humans are exposed to PAHs(Polycyclic Aromatic Hydrocarbons)in soil mainly through ingestion,inhalation and dermal contact,with unconscious oral ingestion being the main route.Therefore,there is an urgent need for an accurate human health risk assessment for ingestion of PAHs-contaminated soil.Initially,risk assessments were based on the total amount of contaminants in the soil,which often resulted in overestimation of health risks.In the last 30 years,researchers have used in vitro gastrointestinal simulations for the determination of bioaccessibility of hydrophobic organic contamination in soil,PBET(Physiologically-based extraction test),CE-PBET(Colon extended PBET),IVD(In Vitro Digestion Model)and DIN(the GermanDeutsches Institut fur Normung method)are commonly used in vitro gastrointestinal simulations for determining the bioaccessibility of PAHs.Although the in vitro digestion model is efficient,inexpensive and easy operation,it cannot simulate the dynamic process of absorption of hydrophobic organic contaminants by the human intestine.In recent years,researchers have considered adding adsorbent materials to the gastrointestinal simulation fluid to maintain the concentration gradient between soil and gastrointestinal simulation fluid.Tenax,C18 membrane,organic silicone,polyethelyne(Poly-E)and polyoxymethylene(POM)are some of the more commonly used adsorbent materials.In this paper,PBET,IVD and DIN methods were selected to couple with the above five adsorbent materials,and the bioaccessibility of 7 PAHs(Benzo(a)anthracene,Chrysene,Benzo(b)fluoranthene,Benzo(k)fluoranthene,Benzo(a)pyrene,Indeno(1,2,3-cd)pyrene,Dibenzo(a,h)anthracen)in site soil was determined after screening of the adsorbent materials.The adsorption efficiency and adsorption capacity of the adsorbent materials need to be verified by kinetics before applying them to in vitro gastrointestinal simulation fluid.Firstly,this paper investigated the kinetics of 3 in vitro gastrointestinal simulation methods coupled with 5 adsorbent materials,and the effects of adsorbent material and above 7 PAHs hydrophobicity on the kinetics.The results showed that DIN coupled with 2 pieces of organic silicone sheets(diameter: 47 mm,thickness: 1.60 mm)had the best kinetics and was able to adsorb 95.0% of PAHs within 116 ± 2.00-155 ± 6.00 min,which was less than the 6 h required for the enteric phase of DIN.Secondly,it was found that the stronger the hydrophobicity of PAHs,the slower the adsorption rate,and among the methods of coupling adsorbent materials by PBET and DIN methods,3(C18membrane,organic silicone sheet,Poly-E)and 2(C18 membrane,organic silicone sheet)adsorbent materials showed a significant negative correlation with the logkow of PAHs,respectively(R2 between 0.60 – 0.88,p < 0.05).Finally,the reproducibility of the adsorbent materials was verified,and the results showed that the organic silicone sheet still had good adsorption performance after 3 repeated elution(p = 0.976),and still had good adsorption performance,which could adsorb more than 96.8% of PAHs when equilibrium was reached.Therefore,DIN coupled with organic silicone sheet was considered to determine the bioaccessibility of PAHs in contaminated soil.7 PAHs site soils with ∑7PAHs concentrations of 35.6 ± 3.74 mg/kg(Soil-7)-259± 2.31 mg/kg(Soil-1)were collected in this study.Among the 7 carcinogenic PAHs detected,Benzo(a)anthracene and Chrysene were predominant in each site soil,accounting for 23.0%-30.5% and 27.8%-37.3% of the total ∑7PAHs concentration,respectively.To assess the extent to which organic silicone sheet improves the in vitro gastrointestinal simulation method,the DIN method without organic silicone sheet was first used to determine the bioaccessibility of PAHs in the 7 site soils in the range of3.18 ± 3.82%-46.9 ± 4.27%.In contrast,the DIN method coupled with organic silicone sheet increased the bioaccessibility by a factor of 2-5,ranging from 16.0 ± 1.82%-90.5 ± 2.89%.The effects of adsorbent materials,soil physicochemical properties,and hydrophobicity of PAHs on bioaccessibility were also analyzed in this paper,and the results showed that the addition of adsorbent materials significantly improved the bioaccessibility determined by DIN method(the absolute value of the standardized regression coefficient Beta was 0.542,β = 0.865),total organic carbon(TOC(%))and black carbon(BC(%))were also two important influencing factors(|Beta| were 0.253 and 0.260 and β were-0.640 and-0.197),means that the higher the TOC(%)and BC(%)content the lower the soil bioaccessibility.Secondly,the stability of the bioaccessibility of PAHs in soils at the organic silicone sheet determination site was verified,and the results showed that there was no significant difference between the bioaccessibility measured 1st and 3rd times in Soil-1(p = 0.087),and the 2nd and 3rd times were only10.0% and 8.60% lower than the 1st time,and there was no significant difference between the 2nd and 3rd times(p = 0.633),indicating that the bioaccessibility of PAHs in soil determined by organic silicone sheet is better reusable.The purpose of determining the bioaccessibility of contaminated soils is to provide precise risk management,therefore,we evaluate the risk assessment of bioaccessibility basede on total amount PAHs,DIN method and DIN coupled with organic silicone sheet.The results showed that the percentage of acceptable carcinogenic risk(ACR)exceeded in 7 soils based on total amount PAHs,DIN method and DIN coupled with organic silicone sheet was 46.9%、8.16% and 30.6%,respectively.The ranges of soil risk control values were 0.06-128、0.29-657、0.15-207 mg/kg,respectively.Due to the ability of DIN coupled organic silicone sheet to simulate human,the risk control of the7 carcinogenic PAHs in the contaminated soil in this study,a control of 0.15-207 mg/kg can be considered as no health hazard to humans.Therefore,the method based on in vitro gastrointestinal simulation coupled with adsorbent materials can avoid overestimation of health risk based on total amount and underestimation of health risk based on bioaccessibility measured by in vitro gastrointestinal simulation. |
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