Abstract:

China is the world’s largest producer and consumer of rice. In some areas heavy metal contamination of paddy soils is a serious problem and poses risks to food security and human health. At present, the major challenge for soil pollution control in China is remediation of paddy soils contaminated with multiple heavy metals. Iron, as the fourth most abundant element in the Earth’s crust and a highly reactive element in soils, is involved in the geochemical processes of many heavy metals. In this review, the mechanism by which iron oxides influence heavy metals, the biochemical process of iron in soils, the effects of iron on heavy metal transformation in soil-rice system, and the application of iron derived materials in the remediation of heavy metal contaminated soils are summarized as the follows: (1) Iron oxides in soils can achieve heavy metal fixation through adsorption/complexation /precipitation, and can reduce heavy metal bioavailability through redox reaction. (2) With change of soil environmental conditions iron oxides are prone to reduction-dissolution/oxidation-precipitation or microbial mediated Fe(III) reduction and Fe(II) oxidation. (3) Change of soil pH and Eh in paddy soils can lead to transformation of iron oxides, formation of iron plaque, and iron uptake by rice, which in turn can affect heavy metal transport in soil-rice system. (4) Iron derived materials show high remediation efficiency for soils contaminated with a single heavy metal, but such materials have not been widely used for remediation of soils contaminated with multiple heavy metals. To provide a reference for addressing this issue this paper discusses the application-related problems and proposes future research directions.

Key words: paddy soil, combined pollution of heavy metals, iron, soil remediation