Bioaccessibility And Health Risk Of Heavy Metals In Soils Based On In-vitro Extraction Methods

Heavy metals exist widely in the environment and possess strong carcinogenicity, teratogenicity, mutagenicity, which have persistent harm to the human body and environment. The approach of "mouth-ingestion" is a major way for heavy metal entering to human body. Bioaccessibility is a very important factor to human health risk assessment. Compared with animal experiments, in-vitro tests method is simpler and faster to evaluate the bioaccessibility of heavy metals, but also can avoid the ethical issues, so it is particularly significant to do research on bioaccessibility of heavy metals.In this study, four representative in-vitro tests methods UBM(unified BARGE method), PBET (the physiologically based extraction test), SBET (simplified bioaccessibility extraction test) and IVG (in-vitro gastrointestinal) were selected to evaluate the bioaccessibility of Pb, Cd, Zn and Ni extracted from different soils with simulating human gastrointestinal juice, and bioaccessibility of heavy metals in the gastric phase and gastrointestinal phase of PBET was also studied. The effects of contents (flour and tea polyphenols) and other in-vitro digestion conditions (such as pH, soil solution ratio and residence time) on heavy metal bioaccessibility was explored. Meanwhile, the bioaccessibility and human health risks of heavy metals (Pb, Cu, Zn and Ni) in soils and dusts in Yangzhou, China were investigated based on in-vitro extraction methods. This study is to provide reference for exactly evaluating the potential risk of heavy metals in soils to human health. The main results are as follows:(1) There were remarkable differences in the bioaccessibility of heavy metals in various soils tested by four in-vitro extraction methods. In most cases, the concents of heavy metals Zn, Ni and Cd in acidic soils by IVG is clearly higher than those by other in-vitro extraction methods, respectively 9.75,6.84 and 0.41 mg·kg-1.while it was found there were higher bioaccessibility of alkaline soil Zn, Ni and Pb by SBET than those by other in-vitro extraction methods, respectively 8.26,4.01,15.0 mg·kg-1. It was found that the bioaccessibility of heavy metals Zn, Ni and Cd in acidic soil by IVG and PBET were higher than that in alkali soil. However, Zn, Ni and Cd bioaccessibility extracted by SBET and UBM in alkali soil were higher than that in acidic soil. It is clear that in-vitro extraction methods, heavy metal species and soil properties had conspicuous influence on bioaccessibility of heavy metals.(2) The bioaccessibility of Pb, Ni and Zn in gastric phase is higher than gastrointestinal phase using PBET except Cu. The extraction concents of Pb, Cu, Ni and Zn in in-vitro was positively related to the total in the soil. Except for Pb, the bioaccessibility of Cu, Ni and Zn using PBET are negatively correlated with soil pH, positively correlation with soil organic matter. Under centain condition, in order to simplify and instant test bioaccessibility of heavy metal, gastric fluid can be used for extraction juice to substitute gastrointestinal fluid.(3) It was foud that the bioaccessibility of Pb, Cu, Ni and Zn reduced with the increase of flour concents, the linear relationship(R2) was more than 0.7892. And the bioaccessibility of Pb, Cu and Zn reduced with the increase of polyphenols concents using SBET and PBET, except Ni.(4) There are many factors can influence heavy metals bioaccessibility. It was indicated that the bioaccessibility of heavy metals increased with the decrease of gastric pH value, soil solution ratio and the increase of retention time,. In order to exactly evaluate the potential risk of heavy metals in soils to human health, it is necessary to choose the appropriate gastric pH value, soil solution ratio and residence time.(5) Based on in-vitro tests, the hazard index values of soil heavy metals to human health in industrial areas is highter than those in other areas (the culture and education areas, commercial areas and scenic areas). The value of hazard index in dust heavy metals in commercial areas is higntest.Using the tests of SBET and PBET, the potential hazard to humans of Pb in soils and dusts in Yangzhou City is highter than other heavy metals (Ni, Cu and Zn), while lowest in Zn. It was also found that the hazard indexs (HI) of heavy metals (Pb, Ni, Cu and Zn) in the soils and dust of Yangzhou city were all less than 1 with SBET and PBET methods. The result suggested that no non-carcinogenic health risks from the studied metals to children via ingestion contact in Yangzhou city.