Co-benefits of biochar-supported nanoscale zero-valent iron in simultaneously stabilizing soil heavy metals and reducing their bioaccessibility.

We investigated the performance and encapsulation mechanisms of novel biochar-supported nanoscale zero-valent iron (nZVI-BC) used for the remediation of soil co-contaminated with arsenic (As), cadmium (Cd), and lead (Pb) via incubation and column experiments. Compared with the control, 0.50% of nZVI-BC significantly decreased the leakage of As, Cd, and Pb by 97.94-98.45%, 42.86-81.12%, and 82.14-92.49%, respectively. In addition, 0.50% of nZVI-BC could transform the fraction of unstable heavy metals into a stable form, which substantially decreased the availability, leachability, and bioaccessibility of the heavy metals and hence greatly reduced the human health exposure risk. Column experiments showed that 0.50% of nZVI-BC effectively restrained the leaching of As, Cd, and Pb by 95.60-99.84%, 70.82-84.18%, and 91.68-99.81%, respectively. The predominant encapsulation mechanisms of nZVI-BC included complexation, precipitation/co-precipitation, reduction, and the formation of ternary surface complexes. Based on these insights, we can devise new strategies for the remediation of soil co-contaminated with As, Cd, and Pb.