Impact of Water and Si Management on As, Cd, and Pb Accumulation in Rice (Oryza sativa L.).

The quality of rice, a staple food for the majority of the world population, may be threatened by the translocation of trace elements from soil to grain resulting in food chain contamination. Therefore, it is imperative to understand the relationship between the bioavailability of trace elements such as Cd, As and Pb in the soil-rice system. Here, we investigated the impact of water and silicon management on As, Pb, and Cd in the soil-water-rice nexus.  We hypothesized that silicon addition and water management would have different impacts on the transfer of trace elements from soil to rice.  To test this, a pot study was conducted in which we manipulated water (flooded, intermittently flooded, non-flooded) and silicon (Si-rich residues of rice husk and ash, 1% w/w) using silicon-depleted soil.  Pore water was monitored through out the study, and at harvest, rice grains, shoots, and roots were analyzed for metal content.  Iron plaque was extracted from roots and utilized for elemental analysis and mineralogical characterization of Fe phases using synchrotron-based X-ray techniques.  We show that Si alteration can affect the quantity and mineralogy of Fe oxide plaque, associated As, and can improve rice yields depending on the choice of amendment.  Results also indicate that the addition of Si-rich rice residues to flooded and non-flooded paddy soil have different impacts on Cd and inorganic As levels in grain.