典型富硒高镉土壤-水稻系统中硒、镉的迁移、转化规律及其健康风险研究

Cadmium (Cd), the primary pollutant of arable soils in China, is highly toxic and carcinogenic. Rice is the staple crop with the highest Cd accumulative ability and represents one of the main sources of Cd exposure. Cd content in rice from polluted areas in China exceeds the maximum of national standards, which threatens food safety and human health seriously. Therefore, it is of vital scientific and social importance to control the environmental risk of Cd polluted soils. Selenium (Se) is one the of essential trace elements for human, exogenous Se not only decreases the toxicity of Cd to rice, but also reduces the absorption and transport of Cd in rice. However, the antagonism between Se and Cd in natural Se rich soils has not been confirmed, the underlying mechanisms are yet to be uncovered. This study aims to (1) analyze the spatial distribution of Se and Cd in soil, and their content and speciation in rice grains thereby illuminating how they are migrated and transformed in a typical Se and Cd rich soil-rice system; (2) investigate the bioaccessibility of grain Se and Cd in gastric and small intestinal phases through an in vitro digestion method and illustrate their interrelationship with hair Se and Cd; and (3) evaluate the long-term health risk of rice containing high Se and Cd in combination with an environmental epidemiological survey in order to improve the quality of agricultural product, guarantee food safety and promote the healthy development of Se industry.

镉是我国耕地土壤的首要污染物，毒性强且有致癌作用。水稻是镉富集能力最强的大宗谷类作物，也是人体镉暴露的主要来源之一。我国镉污染区水稻镉含量超标严重，对食品安全和人体健康构成极大威胁。因此，有效管控镉污染土壤环境风险，具有十分重要的科学意义和社会意义。硒是人体必须的微量元素之一，添加外源硒不仅可以降低镉对水稻的毒害，而且可以减少水稻对镉的吸收与运输。但是，天然富硒土壤中硒、镉是否存在拮抗现象国内外尚未开展深入研究。本项目以典型富硒高镉土壤为研究对象，分析土壤中硒、镉的空间分布特征，以及在稻米中的含量与形态，揭示土壤-水稻系统中硒、镉的迁移、转化规律；通过体外模拟试验，研究稻米中硒、镉在胃肠阶段的生物可给性，以及与人体发硒、发镉之间的关系；结合环境流行病学调查，评估富硒高镉米长期暴露的人群健康风险，为改善农产品质量，保障食品安全，促进富硒产业健康发展提供科学依据。

天然富硒区普遍存在镉背景值偏高的现象，对农作物品质和人体健康有潜在风险。本项目研究了土壤-水稻系统中硒镉的迁移、转化规律，分析了稻米中硒镉的生物可给性，评估了长期膳食暴露的健康风险，并研究了水肥管理等方法对镉的联合阻控作用。研究表明，土壤总硒在0.45‒2.56 mg/kg，总镉0.80–2.65 mg/kg，硒主要以残渣态为主，而镉以可交换态为主，土壤中有效硒和有效镉的摩尔比为0.55，土壤硒对水稻中镉的积累没有明显的拮抗作用；稻米中硒在肠阶段的生物可给性显著高于胃阶段，而镉正好相反；胃肠阶段硒和镉的生物可给性均与稻米中硒和镉的总量呈显著的线性关系。稻米中硒镉摩尔比的对数与硒的可给浓度没有显著的线性关系，但是与镉的可给浓度呈显著的负相关，表明硒镉的摩尔比是决定稻米中镉可给浓度的重要因素。虽然，水稻中镉的积累量远超标准值，但由于硒对水稻中镉生物可给性的拮抗作用并未引起明显的肾中毒现象。由于男性和老年人尿镉和β2-微球蛋白高，尿硒低，因此镉损伤的风险高于女性和中青年。适当的水分管理、硒处理和接种耐硒细菌可以缓解镉对水稻的氧化胁迫，减少水稻对镉的积累，以及向地上部分的运输。