Dosage of Sulfidized Nano Zero-Valent Iron, Soil Moisture and pH Influences on Fraction of Arsenic and Cadmium in Contaminated Paddy Soil

Rice (<i>Oryza sativa</i> L.) exhibits a heightened ability to bioaccumulate arsenic (As) and cadmium (Cd), which directly affects the quality of agricultural products and poses serious risks to both the ecological environment and human health. Due to considerable differences in the occurrence states and chemical behaviors of As and Cd, simultaneous remediation efforts for water or soil contaminated by these elements often prove challenging. Our previous study indicated that the addition of both As and Cd markedly promoted the immobilization of each other by sulfidized nano-zero-valent iron (S-nZVI). To further explore the influence of S-nZVI on the passivation of As-Cd composite contamination, we examined its effect on the residual proportions of As and Cd in the soil by varying the dosage of S-nZVI, the soil moisture content and pH levels. At 2 g·kg^-1 S-nZVI over a 90-day period, residual fraction reached 83% for As and 39% for Cd. When the water content was 100%, residual fractions peaked at 83% for As and 29% for Cd. Additionally, variations in initial pH levels were found to have no significant impact on the remediation efficiency of As and Cd. This suggests that S-nZVI has the ability to sustain the stabilization of As and Cd in soil across diverse environmental conditions. The evident passivation effects on As-Cd composite contaminated soil can effectively reduce the potential ecological risk associated with these contaminants.