Simultaneous mitigation of Cd and As availability in soil-rice continuum via the addition of an Fe-based desulfurization material

Abstract

The simultaneous mitigation of toxic arsenic (As) and cadmium (Cd) in rice grain remains a global challenge. Passivation with natural or artificially modified materials has shown great potential to simultaneously reduce the bioavailability of As and Cd in paddy soils. To date, however, limited materials have are available, with unclear underling mechanisms. Here, a natural iron-based desulfurization material is hypothesized to simultaneously mitigate As and Cd availability in paddy soil-rice continuum, since it is rich in calcium (Ca), iron (Fe), Silicon (Si), manganese (Mn), and sulfur (S). The addition of the proposed material promoted rice growth and reduced soil availability of Cd (extracted with 0.01 mg·L^-1 of CaCl₂) by 88.0-89.6% and As (extracted with 0.5 mg·L^-1 of KH₂PO₄) by 37.9-69.9%. Grain Cd was reduced by 26.4-51.6%, whereas that of inorganic As (iAs) by 33.3-42.7%. The increased Fe (by 44.2%) and Mn (by 178.6%) in iron plaque on the root surface were conducive to the reduction of grain Cd and iAs after application. Furthermore, the maximum adsorption capacities of the proposed material for Cd and As(III) reached 526.31 and 2.67 mg·g^-1, respectively. The coprecipitation with Cd(OH)₂ as a product, Fe-As and Ca-As complexation, and ion exchange of Fe²⁺ released by the material with Cd²⁺ are involved in the mechanisms underlying the available As and Cd reduction. Combining the safety, low-cost, and high accessibility, Fe-based desulfurization material showed great potential for future safe-utilization of As-Cd contaminated paddy soil via passivation.

Keywords: Arsenic; Cadmium; Iron-based desulfurization; Paddy soil, Passivation.