利用体外试验研究活化/钝化修复对土壤砷健康风险的影响及其机理

Unconscious oral ingestion of arsenic-polluted soil has become one of the main sources of arsenic in human body, and the relevant health risk draws broad concern. As countermeasures against soil arsenic pollution, the mobilization/immobilization remediation technologies have been developed. By far, however, the existing evaluation methods could not provide direct and quantitative information about the influence of remediation on the health risk of soil arsenic. In vitro test can be an appropriate tool, by which the digestion and absorption processes in the human gastrointestinal tract are simulated, and accordingly the bioaccessibility/bioavailability of soil arsenic is obtained. In this innovative study, the state-of-the-art in vitro models are to be introduced for studying the influences of the mobilization/immobilization remediation on the health risk of soil arsenic, as well as the relevant mechanisms. The proposed research plan comprises of three parts, including 1) comprehensive investigation of the quantitative relation between the soil properties and the bioaccessibility/bioavailability of soil arsenic; 2) comparative study between the mature and the emerging remediation agents regarding their influences on the health risk of soil arsenic over time; 3) in-depth research on the metabolism of arsenic in the remediated soil by the human gut microbiota. Complying with the Chinese national policy for soil pollution control, this study will contribute to the development of both the health risk assessment and the remediation technologies for arsenic-polluted soil, which its environmental, social and economic significance lie in.

无意地经口部摄入砷污染土壤已经成为人体内砷的主要来源之一，而相关健康风险问题已引起广泛关注。作为降低土壤砷危害的有效途径，活化/钝化修复技术得到了长足发展，但是其对土壤砷健康风险的影响无法通过现有的评价方法进行直接、定量的评估。体外试验方法通过模拟人体胃肠道消化、吸收过程，可获取土壤砷的生物可给性/生物有效性，评估其健康风险。本项目创新性地将先进的体外试验方法与土壤修复技术相结合，研究活化/钝化修复对土壤砷健康风险的影响及其机理，包括：全面综合地探索土壤性质与砷的生物可给性/生物有效性的定量关系模式；对比研究传统与新兴修复剂对土壤砷健康风险的影响及其随时间的变化；深度剖析结肠微生物对修复后土壤中砷的代谢过程。本研究将在砷污染土壤健康风险的精确评估，以及相关修复技术的开发、改进和选择等方面做出关键示范并提供重要科学依据，顺应我国土壤污染防治基本国策，兼具重大的环境、社会和经济意义。

无意地经口部摄入砷污染土壤已成为人体砷贡献率最高的途径之一。尽管不断发展之中的活化/钝化技术乃有效的土壤修复手段，但在其效果及影响评估方面，现有方法无法准确反映人体健康风险方面的信息。本项目创新性地将先进的体内/体外试验方法与土壤修复技术相结合，深入研究活化/钝化修复对土壤砷健康风险的影响及其机理，为相关技术的开发、改进和选择等提供关键科学依据和重要参考，为我国土壤环境质量和人群健康质量的保障做出积极贡献。主要研究内容及核心结果如下：.（1）分别采用多种活化剂（柠檬酸、草酸和Na2S2O4-EDTA）和钝化剂（α-Fe2O3、Fe(0)和CaAl-LDH）对我国五种典型的砷（As(Ⅴ)）污染土壤进行修复，分析其对土壤特定理化性质以及砷的赋存形态等的影响，并结合运用先进的体内试验（小鼠模型）和体外试验（PBET-SHIME联用模型）对土壤砷经口摄入的健康风险的变化进行精确评估和机理探究。结果表明：活化剂方面，Na2S2O4-EDTA在显著增加土壤砷的活跃性的同时增加了其健康风险，建议做好修复过程的风险管控；柠檬酸和草酸在有效活化土壤砷的同时却可显著降低其健康风险，值得推荐。钝化剂方面，传统的α-Fe2O3、Fe(0)和颇具潜力的CaAl-LDH均能显著降低土壤砷的活跃性和健康风险，而CaAl-LDH更是能将活跃态砷直接转化为极稳定的残渣态，对于修复长效稳定性的意义重大，有望推广应用。.（2）肠道微生物主要通过还原和甲基化作用进行土壤砷的代谢，结肠液中观察到较高含量的As(Ⅲ)和不同程度的砷甲基化现象，而残留固相上仅检测出As(Ⅲ)和As(Ⅴ)。活化剂方面，Na2S2O4-EDTA显著增加了结肠液中As(Ⅲ)的含量，进一步增加了土壤砷的健康风险；柠檬酸和草酸却能影响肠道微生物对液相中生物可给态砷的代谢并促进其甲基化，使得高毒性的As(Ⅲ)转化为毒性较低的有机砷，该形态学角度的“解毒过程”进一步降低了土壤砷的健康风险。钝化剂方面，α-Fe2O3或Fe(0)能显著降低结液相中生物可给态无机砷和有机砷含量；CaAl-LDH能极显著降低结肠液中生物可给态As(Ⅴ)含量，令有机砷成为主要形态，进一步降低土壤砷的健康风险。