State Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
Department of Environmental Science and Engineering, Huaqiao University, Xiamen, 361021, China.
Environ Pollut. 2020 Aug;263(Pt A):114580. doi: 10.1016/j.envpol.2020.114580. Epub 2020 Apr 16.
The bioaccessibility of arsenic and its speciation are two important factors in assessing human health risks exposure to contaminated soils. However, the effects of human gut microbiota on arsenic bioaccessibility and its speciation are not well characterized. In this study, an improved in vitro model was utilized to investigate the bioaccessibility of arsenic in the digestive tract and the role of human gut microbiota in the regulation of arsenic speciation. For all soils, arsenic bioaccessibility from the combined in vitro model showed that it was <40% in the gastric, small intestinal and colon phases. This finding demonstrated that the common bioaccessibility approach assuming 100% bioaccessibility would overestimate the human health risks posed by contaminated soils. Further to this, the study showed that arsenic bioaccessibility was 22% higher in the active colon phase than that in the sterile colon phase indicating that human colon microorganisms could induce arsenic release from the solid phase. Only inorganic arsenic was detected in the gastric and small intestinal phases, with arsenate [As(V)] being the dominant arsenic species (74%-87% of total arsenic). Arsenic speciation was significantly altered by the active colon microbiota, which resulted in the formation of methylated arsenic species, including monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] with low toxicity, and a highly toxic arsenic species monomethylarsonous acid [MMA(III)]. Additionally, a high level of monomethylmonothioarsonic acid [MMMTA(V)] (up to 17% of total arsenic in the extraction solution) with unknown toxicological properties was also detected in the active colon phase. The formation of various organic arsenic species demonstrated that human colon microorganisms could actively metabolize inorganic arsenic into methylated arsenicals and methylated thioarsenicals. Such transformation should be considered when assessing the human health risks associated with oral exposure to soil.
砷的生物可给性及其形态是评估人类接触污染土壤健康风险的两个重要因素。然而，人类肠道微生物群对砷生物可给性及其形态的影响尚未得到很好的描述。在这项研究中，利用改良的体外模型研究了肠道中砷的生物可给性以及人类肠道微生物群在调节砷形态中的作用。对于所有土壤，来自组合体外模型的砷生物可给性表明，在胃、小肠和结肠阶段，其生物可给性均<40%。这一发现表明，通常假设 100%生物可给性的生物可给性方法会高估污染土壤对人类健康的风险。此外，研究表明，活性结肠阶段的砷生物可给性比无菌结肠阶段高 22%，表明人类结肠微生物可以从固相中释放砷。在胃和小肠阶段仅检测到无机砷，砷酸盐[As(V)]是主要的砷形态（占总砷的 74%-87%）。砷形态在活性结肠微生物群的作用下发生了显著变化，导致形成了甲基化砷形态，包括毒性较低的一甲基砷酸[MMA(V)]和二甲基砷酸[DMA(V)]，以及一种毒性很高的砷形态一甲基胂酸[MMA(III)]。此外，在活性结肠阶段还检测到高浓度的单甲基单硫代砷酸[MMMTA(V)]（占提取液中总砷的高达 17%），其毒性未知。各种有机砷形态的形成表明，人类结肠微生物可以将无机砷主动代谢为甲基化砷和甲基化硫代砷。在评估与土壤口服暴露相关的人类健康风险时，应考虑到这种转化。
