基于健康风险的稻田土壤甲基汞安全阈值研究

Rice (Oryza sativa L.) is a methylmercury (MeHg) accumulator. Rice consumption has been recognized as one of the primary sources of MeHg exposure for inhabitants in China. MeHg accumulated in rice grain mainly originated from paddy soil. However, to our knowledge, the thresholds for MeHg in paddy soils have not yet been reported. Therefore, the present study will collect typical paddy soils in the main rice producing areas of China and different concentrations of exogenous Hg salts will be added to each soil. Soil MeHg, pH, Eh, and contents of dissolved organic carbon and sulphate will be measured during the aging period in a controlled laboratory experiment, in order to investigate the characteristics and major influencing factors of methylation process of mercury in flooded paddy soils. Then, MeHg and bioavailable Hg concentrations together with soil properties will be measured after the harvest of rice in a pot experiment. MeHg concentrations in rice grains will also be measured. Major controlling factors and prediction models for MeHg accumulation in rice will be identified and developed. The MeHg bioaccumulation factors for different rice cultivars grown in Chinese soils will be collected. The thresholds for MeHg in paddy soils based on safe human MeHg intake (0.23 μg kg·d-1) will be derived using species sensitivity distribution. The results will be of great theoretical importance to the soil chemistry mechanism of MeHg production and bioaccumulation, and will provide an important reference to the revision and improvement of the soil environmental quality standard in China.

水稻是甲基汞的富集植物，食用大米是我国居民甲基汞暴露的一条重要途径。糙米中的甲基汞主要来源于土壤，但稻田土壤甲基汞的安全阈值研究还未见报道。因此，本项目拟采集我国典型水稻土，添加外源汞，通过室内培养实验，测定老化过程中土壤甲基汞及pH、Eh、DOC、硫酸根等的动态变化，探讨土壤淹水过程中汞的甲基化特征及主要影响因素；通过温室盆栽实验，测定水稻收获后土壤甲基汞、有效态汞含量和主要理化性质，以及稻米中的甲基汞含量，探讨影响水稻富集甲基汞的主控因素，并建立预测模型；收集并筛选基于我国土壤的不同水稻品种对甲基汞的富集数据，利用物种敏感性分布法，结合水稻富集甲基汞的预测模型，以人体安全甲基汞摄入量（0.23 μg kg·d-1）为基准，推导我国稻田土壤甲基汞的安全阈值。研究结果对揭示稻田土壤汞甲基化及水稻富集甲基汞的土壤化学机制有重要理论意义，为我国《土壤环境质量标准》的修订完善提供重要参考。

水稻是甲基汞（MeHg）的富集植物，食用大米是我国居民甲基汞暴露的一条重要途径。糙米中的甲基汞主要来源于土壤，但稻田土壤甲基汞的安全阈值研究还未见报道。因此，本项目采集了我国典型水稻土，添加外源汞，通过室内培养实验，测定老化过程中土壤甲基汞及原位pH、Eh的动态变化，研究了土壤淹水过程中汞的甲基化特征及主要影响因素，结果表明，土壤有机质含量是控制外源汞进入土壤后甲基化的主要影响因素，利用土壤原位pH和Eh或者风干土壤样品的有机质含量和淹水时间都可以很好地预测土壤汞的甲基化率；通过温室盆栽实验，阐明了不同水稻品种富集甲基汞的敏感性差异，土壤MeHg和有机质含量是影响水稻富集MeHg的主要影响因素，二者可以很好地预测糙米中的MeHg含量；收集并筛选了基于我国土壤的不同水稻品种对甲基汞的富集数据，利用物种敏感性分布法，结合水稻富集甲基汞的预测模型，以人体安全甲基汞摄入量为基准，推导出了我国稻田土壤甲基汞的安全阈值。研究结果对揭示稻田土壤汞甲基化及水稻富集甲基汞的土壤化学机制有重要理论意义，为我国《土壤环境质量标准》的修订完善提供了重要参考。