铁硫耦合影响土壤-水稻系统中甲基汞迁移转化的机制研究

The health risks of methylmercury accumulation in rice is attracting much attention,and it is signifance for taking effective measures to control methylmercury accumulation by revealling the mechanism of coupling of iron and sulfur effect on methylmercury migration and transformation in the soil-rice system. Methylmercury in rice come mainly from paddy soil. Spatial variability of iron and sulfur content in the paddy is much. With the alternating wet and dry and radial oxygen loss from rice roots in the rice cultivation process, the interaction of iron-sulfur modify with the their speciation changed and result in the change of methylmercury concentrations and bioavailability.The factors effect on methylmercury content in planted soil will be determined by sand-soil pot experiments planted with rice under the conditions of the coupling of iron-sulfur.By the means of solution experiment and pot experiment, iron plaque on the rice roots react by the coupling of iron-sulfur and play the roles of methylmercuy moving into roots by using of TEM technique. The mechansim of methylmercury migration will be revealled by stimulation experiment with the iron-sulfur coupling in this projectts. At last, the mechanism of migration and transformation of methylmercury in the soil - rice system will be put forward on the conditions of the iron-sulfur coupling, and which provides a theoretical base to control the accumulation of methylmercury in the rice by improving the content relationship of iron and sulfur.

甲基汞在水稻中的积累而产生的健康风险倍受关注。水稻中甲基汞主要来源于稻田土壤，土壤中铁硫含量空间变异大，在水稻种植过程中因干湿交替作用与根系泌氧影响铁硫的相互作用，使土壤甲基汞的含量及其迁移速率发生变化，从而影响其生物有效性。揭示铁硫耦合影响甲基汞在土壤-水稻系统中迁移转化机制对调控水稻甲基汞含量具有重要意义。本项目通过沙土联合培养水稻盆栽试验，明确铁硫耦合下土壤-水稻系统的土壤中甲基汞含量的受控因子；通过溶液培养和土壤盆栽试验，借助扫描电镜等测试技术确定铁硫耦合下水稻根表铁膜的响应及其在甲基汞进入根系过程中扮演的具体角色；通过模拟试验，揭示铁硫耦合下甲基汞在土壤-水稻系统中迁移的受控机制。最后，力求揭示铁硫耦合影响甲基汞在土壤-水稻系统中迁移转化的机制。通过改善土壤中铁硫对比，为降低汞污染区水稻甲基汞含量提供理论支撑。

具有较强神经毒性的甲基汞成为了汞污染区以稻米为主食的当地居民甲基汞暴露主要途径，对人体健康产生潜在威胁。稻田土壤是水稻吸收积累甲基汞的潜在库。如何有效的降低水稻中甲基汞含量迫在眉睫。在水稻生长季节，铁硫因干湿交替发生氧化还原作用改变其化学形态而影响土壤-水稻系统中甲基汞迁移转化但其影响机制仍然模糊。.（1）通过室内培养试验、野外调查和根箱试验研究了铁、硫对汞甲基化作用的影响。培养试验结果表明汞污染稻田土壤中添加不同形态的铁促进汞甲基化。加硫酸亚铁处理的培养25天后，其甲基汞含量是对照的1.6倍。在贵州万山汞污染区调查水稻发现根表铁氧化物与根际区甲基汞含量具有较好的相关性。利用水稻根箱盆栽实验研究了铁硫对根际外不同距离的甲基汞含量的影响。结果表明，铁处理非根际土壤甲基汞含量变化在1-5 mm范围内均呈现倒“V”形式，在3mm处达到最大。加硫提高了非根际土壤中甲基汞的含量，其甲基汞的含量是对照的2倍以上。铁硫耦合提高了非根际土和根际土壤中甲基汞含量，硫酸盐加铁处理的甲基汞含量呈现增加的趋势，总体变化幅度在112.2-139.6 ng/g。.（2）在溶液培养条件下，60 mg Fe/L诱导处理的根中甲基汞浓度仅为未加铁处理的39.7%，根表铁膜起到屏障作用。但在万山汞矿区调查发现，水稻不同器官中吸收的甲基汞量与根表铁膜量无明显的相关性。反映在不同环境下的根表铁膜对水稻吸收甲基汞影响存在不同的机制。.（3）在水稻生长初期，通过加入铁盐，其精米中甲基汞含量仅为对照的70.1%。与对照相比加半胱氨酸也可降低了精米中甲基汞含量5%。铁硫耦合作用提高了根、茎和叶中总汞的浓度，但是铁和硫酸盐以及铁和半胱氨酸相互作用，精米中甲基汞的浓度相应降低了36.4%和48.2%。. 以上研究结果，充分反映了铁对稻田土壤汞甲基化作用和水稻吸收甲基汞产生了显著的影响，该研究结果为汞污染区根据土壤特性利用外源铁降低水稻精米中甲基汞含量提供了理论基础。