污染土壤中砷对人体生物有效性的体外试验研究

Arsenic (As) pollution is a serious global health problem. It is driven by exposure to naturally occurring sources and human activities. Exposure to excess As can lead to cancers of the lung, liver, bladder and kidney. Human can be exposed to As by eating food, drinking water, or breathing air. Children may also be exposed to As by incidental eating soil. In recent year, soil ingestion from incidental hand-to-mouth activity by children is thought an important issue in assessing public health risks associated with exposure to As contaminated soils.The toxicity of arsenic is depended on its speciation. Although inorganic As may be the predominant form in contaminated soils, soil As speciation changes during gastrointestinal transit are not well characterized. Therefore, we can not accurately assess the risk of soil As for human based on the total soil As. .In this project, in vitro degestion/caco-2 cell model was constructed, optimized and used to study As bioaccessibility and bioavailability in the typical contaminated soils collected from our country. The soil As sources are metal mining, industrial production, pesticides, manure, chemical fertilizers and coal-fired fly ash. The study will characterize the chemical speciation of As with method of Wenzel et al (2001) and in vitro degestion/caco-2 cell model. The HPLC-ICP-MS will be used to determined the speciation and the concentration of As. The aims of the study are: to determine the bioaccessibility and bioavailability of the different As speciation in the selected soils; to identify the As speciation changes and to understand their mechanism in the gastrointestinal phases; to compare chemical speciation of As with method of Wenzel et al (2001) with the results of in vitro degestion/caco-2 cell model; to compare and identify As speciation in soils, degested solution and Caco-2 cell uptake; to evaluate the doses that human exposure to different of As speciation from the selected soils. This research will not only play an important role in promoting the theory and methodology in the bioaccessibility and bioavailability of soil As and using it to assess human health risks of As uptake and accumulation but also provide some scientific understanding in developing standards and regulations to effectively prevent As poisoning to the humanbeing.

人体无意摄入土壤砷是人体砷暴露的主要途径之一。不同形态和价态砷对人体的毒性差异很大。相对于土壤中的总砷，土壤中不同形态和价态的砷在人体消化道中的转化及其生物有效性更能准确地反映出土壤砷对人体的毒性。本项目拟利用改进的体外消化/Caco-2细胞模型这一体外试验方法体系研究我国典型砷污染土壤（包括金属矿山开采、工业生产、农药、畜禽粪便和化学肥料使用、燃煤产生的飞灰和灰渣等对造成的砷污染土壤）中总砷、无机砷及有机砷的人体生物有效性。分析体外试验中土壤无机和有机砷的释放和转化规律并明确主要的影响因素；阐明不同形态和价态砷在土壤、体外消化及Caco-2细胞吸收中的关系；确定不同源土壤中不同形态和价态砷的人体生物有效性及其对人体总砷暴露量的贡献。本项目的研究将对土壤砷的人体生物有效性及其对人体健康风险研究的理论与方法起到极大的推动作用，也将为我国未来制定针对土壤中不同形态和价态砷的控制标准提供依据。

项目主要针对典型砷污染土壤，通过建立体外胃肠方法/SHIME模型/Caco-2细胞模型研究土壤中砷的生物可给性、砷形态转化以及细胞吸收。主要的研究工作包括污染土壤中砷的生物可给性及动态溶出的研究；不同体外胃肠方法与SHIME联用的对比；肠道微生物对土壤砷的代谢：砷的形态及分布；土壤砷代谢物的肠道吸收等。主要的结论如下：（1）土壤中砷的生物可给性及生物可给态含量差异很大。多数土壤中小肠阶段砷的生物可给性均高于胃阶段。胃肠阶段砷的生物可给态含量与土壤总砷和无定形铁锰氧化物呈显著正相关性。不同土壤中砷的溶出在胃肠阶段有明显的差异。（2）五种体外方法间胃阶段、小肠阶段及结肠阶段砷的生物可给性均呈现出显著差异性。SBRC-SHIME和PBET-SHIME两种方法结肠阶段砷的生物可给性较接近动物实验砷的相对生物有效性。结肠阶段，不同方法间砷形态及含量有显著差异。微生物还原作用导致大量As(III)的产生；UBM-SHIME方法表现出较高的甲基化程度而SBRC-SHIME方法甲基化程度较低。结肠阶段砷的生物可给性是小肠阶段的1.8-2.8倍。（3）肠道微生物对土壤砷的代谢能力不同。As(V)的还原作用产生了大量的As(III)；甲基化程度显著不同，甲基砷比例达到6.1-31.1%。XANES分析结果显示，原始土壤固相上砷主要以As(V)存在；结肠阶段，土壤固相上As(III)所占比例均升高，达到16.6-26.9%和73.4%，As(V)还原产生的As(III)一部分停留在土壤固相上。肠道微生物有能力释放土壤砷，尤其是依附于无定形的铁/铝氧化物。固液两相砷形态的变化显示，结肠阶段，微生物还原产生大量的As(III)，其中44.2-97.6%停留在土壤固相上。肠道微生物对液相砷的代谢速度快于固相。（4）Caco-2细胞模拟人体肠道吸收实验显示，不同砷形态间的细胞吸收差异明显。MMA(V)和As(III)的吸收率略高于DMA(V)和As(V)。此外，MMMTA(V)的吸收率达到了41.6%。本项目的研究将对土壤砷的人体生物有效性及其对人体健康风险研究的理论与方法起到较好的推动作用，也将为我国未来制定针对土壤中不同形态和价态砷的控制标准提供参考。