Arsenic sequestration in iron plaque and its effect on As uptake by rice plants grown in paddy soils with high contents of As, iron oxides, and organic matter

Abstract

The aim of this study is to investigate the effects of the rice (Oryza sativa L.) root's iron (Fe) plaques on arsenic (As) uptake by rice plants grown in As-contaminated soil with high contents of iron oxides and organic matter, from the Guandu Plain of northern Taiwan. The results of the soil incubation study show that both As and Fe concentrations in the soil solutions increased with flooding time due to reductive dissolution of iron oxides induced by the soil's high contents of organic matter. Large Fe plaques were deposited on rice roots and substantial amounts of As were sequestrated in these Fe plaques. About 73.8 to 90.4 % of the total As released from soils was distributed in the iron plaques and only a small proportion was distributed in the rice plants. This study provides evidence that iron plaques are the main controlling factor in limiting the uptake of As into the rice plants grown in the tested soils, and that iron plaque formation enhancement could be used to reduce As uptake by paddy rice grown in As-contaminated soils, thus reducing As toxicity.