Objective The purpose of this study was to find effective and affordable effective passivation agents used in the remediation of cadmium (Cd) -arsenic (As) co-contaminated farmland soil, which would play an important role in protecting food security and human health.
Method A soil-based incubation experiment was carried out by utilizing paddy soil that had been contaminated with Cd-As. The effects of various passivators (i.e., CaCO3 (CA), rice straw (JG), and rice straw biochar (SW) ) on the immobilization of Cd and As, as well as on soil fertility index and soil enzyme activities, were analyzed in order to find the most suitable passivators in reducing Cd and As availabilities and in maintaining soil eco-function.
Result The results showed that the toxic leaching amounts of Cd decreased by 6.13%, 8.97% and 12.3% in comparison to control (CK), and the toxic leaching amounts of As decreased by 9.02%, 4.24% and 5.42% in CA, JG and SW treatments, respectively. The residual Cd and As levels increased by 12.2% and 12.1% in CA treatment, and by 28.7% and 15.1% in SW treatment. Compared with CK, soil pH, organic matter, total nitrogen, and total phosphorus content increased significantly in all three treatments. The SW treatment had the highest levels of soil organic matter, total nitrogen, and total phosphorus, which increased by 7.51%, 9.14% and 15.6%, respectively, compared with CK. Additionally, soil alkaline phosphatase and protease activities significantly enhanced by 35.3% and 12.2% in SW treatment compared to CK.
Conclusion As shown by the efficient reduction of Cd and As effectiveness and the improvement of soil fertility and ecological functions, adding biochar has clear benefits in the remediation of Cd-As co-contaminated soil, making it a good remediation material for heavy metal contaminated soil, particularly in Cd-As co-contaminated soil.
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