腐殖酸对汞污染稻田中甲基汞行为的影响

摘要

近期研究表明汞矿区水稻中汞富集可能对居民健康产生潜在威胁。因此，研究关键生物地球化学因素对于稻田汞，特别是甲基汞（ MeHg）的形态及其植物可利用性的影响显得尤为重要。通过温室土培试验，探究汞污染土壤中添加腐殖酸对于甲基汞的生成及水稻甲基汞富集的影响。结果表明，腐殖酸的添加可显著降低土壤中汞的甲基化（抑制甲基化效应），相比对照组，腐殖酸组土壤甲基汞浓度时间加权平均值显著下降41�7％，然而土壤间隙水中甲基汞浓度（时间加权平均值）却显著增加277�0％，这可能是由于间隙水中溶解性有机质浓度的增加（甲基汞溶出效应）。水稻地上部组织中富集的甲基汞总量也相应增加25�6％。此外，腐殖酸的加入还导致甲基汞的转运系数显著增加（甲基汞转运效应），糙米中甲基汞总量也显著增加26�4％。与此同时，腐殖酸的加入促进了水稻产量的增加（25�4％），从而稀释了糙米中甲基汞浓度（甲基汞生物稀释效应）。最终，腐殖酸处理组糙米甲基汞浓度与对照组甲基汞浓度相当。%Recent studies have reported that mercury accumulation in rice grains produced in Hg mining area may pose a potential health risk to consumers of the rice. Therefore, it could be of great importance to investigate how some key bioge⁃ochemical factors affect speciation and phytoavailability of mercury ( especially methylmercury, MeHg) in contaminated paddy soils. A pot experiment was carried out in greenhouse to investigate effects of addition of humic acid on production, phytoavailability, and bioaccumulation of methylmercury in an Hg⁃contaminated paddy soil. Results of the experiment show that addition of humic acid significantly reduced mercury methylation in the soil ( methylation⁃inhibiting effect) by 41�7%in terms of time⁃weighted average concentration, as compared with CK, while it increased even more or by 277�0% of methylmercury in the soil porewater in terms of time⁃weighted average concentration, which may be attributed to the elevat⁃ed concentration of dissolved organic matter in the porewater ( methylmercury mobilizing effect) . Consequently, the amount of methylmercury accumulated in shoot of the rice plants increased by 25�6%. Furthermore, the addition of humic acid caused significant increase in methylmercury translocation coefficient from soil to rice grains ( methylmercury translocating effect) , thus leading to an evident increase ( 26�4%) in methylmercury accumulation in rice grains. However, the addition of humic acid also increased biomass of rice grains by 25�4%, thus diluting methylmercury concentration in grains ( methylmercury biodiluting effect) . Consequently, the treatment of addition of humic acid and the treatment of CK were more or less the same in methylmercury concentration in grain.