Effects of combined applications of S-nZVI and organic amendments on cadmium and arsenic accumulation in rice: Possible mechanisms and potential impacts on soil health

Abstract

In situ remediation of cadmium (Cd) and arsenic (As) (Cd&As) contaminated soil using iron-based materials has been extensively investigated. Simultaneous immobilizing Cd&As with iron-based materials while maintaining soil health poses a significant challenge. This study examined the effects of sepiolite-supported nanoscale zero-valent iron (S-nZVI) combined with organic amendments (RS: Rice straw; PM: Pig manure) on Cd&As uptake by rice and soil quality. Grain Cd (0.134 mg kg⁻¹) and inorganic As (iAs) (0.099 mg kg⁻¹) levels in S-nZVI+PM treatment were reduced by 78.95 % and 68.69 % compared to CK (P < 0.05), and decreased by 52.62 % and 17.50 % compared to S-nZVI treatment (P < 0.05), significantly lower than the Chinese Food Safety Standard (<0.20 mg kg⁻¹). The elevated soil pH, increased amorphous iron (Feox), and PM complexation co-contributed to Cd immobilization in S-nZVI+PM treatment; concurrently, the higher Feox maintained lower available As levels in paddy soil. In addition, S-nZVI+PM improved soil fertility, functional enzyme activity, soil bacterial community diversity, and increased brown rice yield. However, S-nZVI+RS facilitated the reductive dissolution of Fe(oxy)(hydro) oxides and As methylation in paddy soil, significantly increasing the total As and organic As content in grains by 113.13 % and 236.79 %, respectively, compared to S-nZVI treatment. Caution should be exercised in the application of S-nZVI+RS in As-contaminated paddy soil. S-nZVI+PM proved more effective in immobilizing Cd&As and provided greater benefits to soil quality compared to S-nZVI+RS. Overall, S-nZVI+PM represents an eco-friendly approach for alleviating Cd&As accumulation in rice grains while concurrently improving soil health.