Effects Of Calcium,Iron,and Zinc On Human Bioavailability Of Arsenic And Lead In Soils

Arsenic（As）and lead（Pb）are heavy metal pollutants that have garnered significant attention due to their potential for ingestion by the human body through soil matrices,leading to accumulation within the body and posing a threat to human health.In vitro gastrointestinal simulation models（PBET assay）and in vivo animal experiments（mouse model）have been commonly employed to investigate the human bioavailability of heavy metals in soils.The human bioavailability of heavy metals in soils is typically affected by various factors,including measurement methods（in vitro and in vivo）,soil physicochemical properties,and heavy metal morphology.Recently,researchers have discovered that food composition also significantly impacts the human bioavailability of heavy metals.However,only a few studies are reporting on how calcium（Ca）,iron（Fe）,and zinc（Zn）affect the human bioavailability of As and Pb in soils.In this thesis,we investigated soils contaminated with As and Pb from Shuikou,Hunan,and Jiyuan,Henan.Specifically,we examined the changes in bioaccessibility and speciation of As and Pb in soils during the human gastrointestinal digestion stage following oral ingestion of mineral elements such as calcium nitrate（CaNO₃）,ferrous sulfate（Fe SO₄）,and zinc sulfate（Zn SO₄）.This was achieved by combining the PBET experiment with the Tessier sequential extraction method.Based on this premise,a mouse model was utilized to investigate the impact of various mineral elements（calcium sulfate（CaSO₄）,ferrous sulfate（Fe SO₄）,zinc sulfate（Zn SO₄）,and calcium carbonate（CaCO₃））as well as commercially available mineral supplements(calcium carbonate（CaCO₃）,ferrous sulfate（Fe SO₄）,and zinc gluconate(C₁₂H₂₂O₁₄Zn))on the relative bioavailability of As and Pb in soils.Transmission electron microscopy（TEM）and high-throughput sequencing of 16S rRNA were employed to detect and analyze the structure of liver tissue and intestinal microbial community in mice exposed to As and Pb after the intervention of Ca,Fe,and Zn.The aim was to investigate the mechanism underlying changes in the relative bioavailability of As and Pb in soils resulting from alterations in liver tissue and intestinal microbial community structure.The primary findings of the experiments are outlined below:（1）The PBET method was employed to investigate the influence of Ca,Fe,and Zn on the bioaccessibility of As and Pb in soils.Results showed that the addition of Cacould reduce the bioaccessibility of As in the gastrointestinal phase while increasing the bioaccessibility of Pb in the gastric phase and decreasing it in the intestinal phase.On the other hand,Fe and Zn were found to effectively reduce the bioaccessibility of both As and Pb during gastrointestinal digestion.The correlation analysis between the available data of As and Pb and the continuous extraction data showed that for As,the addition of mineral elements mainly promoted the transformation of the reduced available As in the gastric phase to the exchangeable,carbonate-bound and Fe/Mn oxides-bound As in soils,while the reduced available As in the intestinal phase mainly migrated to the exchangeable,carbonate-bound,Fe/Mn oxides-bound and organic-bound As in soils.For Pb,the increased available Pb in the gastric phase after the addition of mineral elements was mainly attributed to the dissolution of exchangeable,carbonate-bound,and organic-bound Pb in soils.In contrast,the decreased available Pb in the intestinal phase was primarily transformed into Pb bound to carbonates and Fe/Mn oxides in soils.（2）In vivo experiments with mice were conducted to investigate the effects of varying concentrations of Ca,Fe,and Zn elements on the relative bioavailability of As and Pb in soils.It was found that,comparing CaSO₄,Fe SO₄,and Zn SO₄,the addition of Ca（500-10000 mg/kg）was the most effective in reducing the relative bioavailability of As and Pb in soils,which decreased from 23.52%-24.47%to 7.62%-19.96%for As and 35.59%-54.47%to 19.96%-29.97%for Pb;followed by Fe（6-600 mg/kg）,while the addition of Zn（30-1000 mg/kg）increased the relative bioavailability of As but decreased the relative bioavailability of Pb in soils.Moreover,the addition of CaCO₃ resulted in a significant decrease in the relative bioavailability of As（8.96%-18.97%vs.7.62%-19.96%）and Pb（13.08%-33.92%vs.19.96%-29.97%）in soils compared to the CaSO₄ treatment.（3）Based on TEM observations,exposure to As and Pb in soils could induce hepatic damage in mice.Interventions with Ca,Fe,and Zn could facilitate the recovery of liver function by enhancing intestinal barrier integrity,mitochondrial quantity,and morphology,thereby modulating the absorption of As and Pb in mice.The 16S rRNA sequencing method was employed to analyze the intestinal microbial community of mice and investigate the regulation effects of Ca,Fe,and Zn on gut dysbiosis in As-and Pb-exposed mice.The findings indicated that CaSO₄,Fe SO₄,and Zn SO₄ positively affected intestinal health by modulating gut microbiota composition,augmenting the abundance of beneficial bacteria,and mitigating intestinal inflammation.（4）In vivo experiments were conducted on mice to investigate the impact of varying concentrations of commercial Ca,Fe,and Zn supplements on the relative bioavailability of As and Pb in soils.The findings indicated that the supplementation of Caand Fe decreased the relative bioavailability of As.In contrast,Zn exhibited a dose-dependent response,with no significant effect observed at low concentrations（30-200 mg/kg）but a substantial increase in the relative bioavailability of As at higher concentrations（500 mg/kg）.Additionally,Ca,Fe,and Zn supplements could all reduce the relative bioavailability of Pb,with Casupplements showing the most significant effect,followed by Fe and Zn supplements.Compared to Ca,Fe,and Zn elements,the effects of Ca,Fe,and Zn supplements on the relative bioavailability of As and Pb in soils were similar but more significant.（5）TEM observation revealed that high-dose Ca,Fe,and Zn supplements had negligible impact on ameliorating hepatic damage in mice exposed to As and Pb.Compared to the soil group,the high-concentration CaCO₃ co-exposure group exacerbated liver tissue damage in mice,as evidenced by increased lipid droplets and abnormal mitochondrial morphology.Furthermore,high-throughput techniques were employed to investigate the impact of Ca,Fe,and Zn supplementation on alterations in the gut microbiota of mice exposed to As and Pb.These findings indicated that high-dose Caand Fe supplements did not significantly alleviate the gut microbiota disorder induced by As and Pb exposure.In contrast,Zn supplements improved the Firmicutes to Bacteroidetes（F/B ratio）,altered microbial structure,and rendered the flora composition of As-and Pb-exposed mice develop to the control group.