Biochar potential to relegate metal toxicity effects is more soil driven than plant system: A global meta-analysis

Abstract

Pollution from potentially toxic metals (PTMs) is one of the most pressing global environmental challenge with soaring human health concerns. It is now critical to seek out effective remediation technologies to control PTMs in the terrestrial environment. Biochar has piqued the interest of researchers due to its ability to immobilize PTMs, particularly in soil, with the assumption that biochar having unique physico-chemical properties may influence PTM mobility. A meta-analysis was performed using 1503 observations extracted from 80 peer-reviewed articles to determine: (a) the effects of various physico-chemical properties of biochar on the bioavailability of PTMs (As, Cd, Cu, Ni, Pb, Zn) in soil and plants, and (b) the best specification of physico-chemical properties of biochar for effective remediation of these PTMs. The findings revealed that the reduction rate of PTM bioavailability is heavily influenced by the physico-chemical properties of both biochar and soil. The physico-chemical parameters of biochar that have effective response to PTMs immobilization were as; 101–500 m2 g−1 surface area, neutral to alkaline pH, pyrolysis temperature > 500 °C, with best application rate of 1.1–3%. However, overall results indicate that the biochar, with given specification of physico-chemical attributes, can decrease the bioavailability of PTMs by 40% in soil and 22% in plants. Moreover, edaphic factors such as soil pH, texture, and crop type can also influence the biochar mediated PTMs adsorption and transformation under field or pot conditions. Furthermore, research gaps remain to be filled in order to investigate the efficiency, high specificity, and secondary pollution aspects of biochar, particularly on large-scale applications as an amendment for PTM remediation.