Remediation of multi-metal contaminated soil using biochars from rice husk and maple leaves

Influence of four different types of amendments [raw rice husk (RRH), rice husk biochar (RHB), raw maple leaves (RML), and maple leaf biochar (MLB)] at the low application dosages (0.5, 1, and 2% w/w) was investigated on (im)mobilization of Cd, Cu, Pb, and Zn in an agricultural soil. A greenhouse experiment using mustard green “Brassica juncea” was conducted to evaluate the efficiency of soil amendments on bioavailability of metals. Metal leaching was remarkably decreased at biochar-treated samples, which was primarily attributed to biochar-induced increase in soil pH. Application of RRH and RML (2%), however, slightly increased heavy metal mobilization because of their acidic nature. Both biochars incorporation induced a considerable decline (> 80%) in the phytoavailability of metals. Generally, maximum immobilization efficiency for Cd, Cu, Pb, and Zn was observed in the case of RHB and MLB (2%), MLB (2%), RHB (2%), and RHB (2%) treatments, by 61–62%, 71%, 76%, and 40%, respectively. A comparison between various application dosages of amendments showed a noticeable difference between 0.5% and 2% for metal immobilization. Overall, results demonstrated the efficacy of several amendments for metals (im)mobilization while stressing the need to measure simultaneously the leaching and phytoavailability of metals induced by amendments.