The translocation of antimony in soil-rice system with comparisons to arsenic: Alleviation of their accumulation in rice by simultaneous use of Fe(II) and NO3−

Abstract

Antimony (Sb) accumulation in rice grains is a potential risk to human health. This study aims to develop agronomic practices that can reduce the accumulation of Sb in rice grain in contaminated soil. A pot culture experiment was conducted to investigate the effects of co-application of ferrous iron and nitrate (Fe(II) + NO3−) in paddy soils on Sb uptake by rice. The co-application of Fe(II) and NO3− promoted abiotic/biotic Fe(II) oxidation and mineralization in the rhizosphere soil and formation of Fe plaques, consequently, Sb bioavailability was significantly reduced by enhancing Sb immobilization on the newly formed Fe(III) (hydr)oxides. The results were compared with those for arsenic (As) in the same trial and it was shown that the two metalloids have different translocation behavior in the soil–rice plant system. The adsorption of Sb, especially the Sb(V), on Fe(III) (hydr)oxides was more significantly enhanced by the decreased soil pH after the application of Fe(II) + NO3− than that of As. The uptake of Sb by the roots of rice was much more difficult but it was much easier to be transported from the rice straw to the grains compared to As. The differences might be mainly caused by the different uptake mechanisms of Sb and As by rice plants from paddies. The bioavailable As(III) would be much more efficient in entering into the rice roots than Sb(III) through the aquaporin channel due to its much smaller ionic radius; the bioavailable As(V), entering into the rice roots via phosphate transporters, would also be more efficient in taking up by roots than Sb(V), which pathway from soil to rice roots remains unclear. These findings provide new insights into Sb biogeochemical behavior in soil–rice plant systems and demonstrate that co-application of Fe(II) and NO3− could be a promising strategy for safely-utilizing Sb contaminated sites in the future.