Health Risk Assessment Of Heavy Metals And Semi-volatile Organic Pollutants On The Site Based On Bioaccessibility

Human health risk assessment technology is one of the decision-making auxiliary tools for the remediation and treatment of contaminated sites.At present,health risk assessment is mainly based on the total amount of pollutants in contaminated sites,which will lead to excessively strict soil remediation targets and excessive waste of remediation funds.In order to overcome these shortcomings,this paper takes heavy metals(Cr,Ni,Cu,Pb)in chromium salt plants and polycyclic aromatic hydrocarbons(PAH)in coking,steel and pesticide plants as examples,referring to the method of the German Institute of Standards(DIN-19738,abbreviated as “DIN”),which simulates the human gastrointestinal digestive environment,systematically studies the bioaccessibility of pollutants under the conditions of simulated fasting and eating(milk powder,apple),and explores the effect of soil physical and chemical properties on bioaccessibility.Based on bioaccessibility parameters to assess the health risk level of site pollutants to human body.The research content and results are as follows:1.Chromium Salt PlantIn the soil of the chromium salt plants,the content of Cr is the highest,exceeding the control value of the second-class land in GB 36600-2018,causing serious pollution.In vitro experiments,the bioaccessibility of Cr,Ni,and Pb in the gastric phase was higher than that in the intestinal phase;the bioaccessibility of Cu in the intestinal phase was significantly higher than that in the gastric phase.Compared with the fasted state,the addition of milk powder has less effect on the bioaccessibility of Cr and Ni,while the addition of apples will reduce the bioaccessibility of Cr and Ni;the addition of apples and milk powder will increase the bioaccessibility of Cu and Pb,and the effect of adding milk powder is more significant.The content of organic matter in the soil showed a significant negative correlation with the bioaccessibility of heavy metals Cr(P<0.05),that is,the higher the organic matter content,the lower the bioaccessibility of Cr.Compared with the total assessment based on Cr,with the bioaccessibility correction of Cr,the remediation target value of Cr in the soil increased by 0.3~46.6 times.2.Coking PlantThe benzo[b]fluoranthene(BbF),benzo[k]fluoranthene(BkF),benzo[a]pyrene(BaP)and dibenzo[a,h]anthracene in the soil of a coking plant in Hebei were studied(DBA),indeno[1,2,3-cd]pyrene(IPY),benzo[g,h,i]perylene(BPE)six kinds of PAHs,whose content is between 8.2~68.3 mg/kg,serious pollution,especially around the tar refining workshop.The results of in vitro experiments showed that the bioaccessibility of the six PAHs ranged from 13.5% to 56.4%,with an average value of 38.5%.Compared with the fasting state,the addition of apples has little effect on the bioaccessibility of PAHs,while the addition of milk powder will increase the bioaccessibility of PAHs.At the same time,the soil cation exchange capacity has a significant effect on the bioaccessibility of the six PAHs(P<0.01),that is,the higher the cation exchange capacity,the smaller the bioaccessibility of PAHs.Compared with the full assessment of PAHs,based on PAHs bioaccessibility correction,the carcinogenic risk of BbF,BkF and BaP all decreased by an order of magnitude,the carcinogenic risk of IPY and DBA decreased within the same order of magnitude,the remediation target value is increased accordingly.3.Comparative Study of PAHs in Different Contaminated SitesFive PAHs(Fluoranthracene(FLT),Pyrene(PYR),benzo[b]fluoranthene(BbF),benzo[a]pyrene(BaP),indeno[1,2,3-cd]pyrene(IPY))in the surface soil of four sites in a Beijing coking plant(BJ),a Shandong steel plant(SD),a capital steel plant(SG)and a Dalian pesticide plant(DL)were studied,the highest content of PAHs in BJ site(116.9~407.1 mg/kg),followed by SD and SG sites(46.6~189.7 mg/kg),and the lowest in DL sites(1.1~14.0 mg/kg).The results of DIN in vitro experiments showed that the bioaccessibility of PAHs in the soil of the four sites BJ,SD,SG and DL were 1.2%~4.2%,5.5%~15.7%,11.2%~18.0% and 15.3%~68.5%.Compared with fasting,the addition of apples has little effect on the bioaccessibility of the five PAHs,while the addition of milk powder can significantly improve the bioaccessibility of PAHs.When the risk assessment is based on the full amount,the carcinogenic risks of BbF,BaP,and IPY in the four sites all exceed human acceptable risk levels;after the introduction of their bioaccessibility corrections,the carcinogenic risks are all reduced by one to two order of magnitude,the carcinogenic risks of BbF in SD sites,BbF,BaP and IPY in DL sites are all reduced to human acceptable risk levels.Studies have shown that assessing human health risks based on the bioaccessibility of pollutants and formulating remediation target can effectively solve the problem of excessively severe soil remediation target and excessive remediation based on total assessment,and save hundreds of millions of remediation funds for the country.It is hoped that this research can provide a reference for the scientific remediation of sites contaminated by heavy metals and semi-volatile organic compounds in China.