Cannabis sativa L. Phytoremediation of Heavy Metal Soil Contamination, Followed by Biomass Valorization

Soil heavy metal contamination poses a major environmental threat, negatively impacting ecosystems, agricultural productivity, and human health. Phytoremediation offers eco-sustainable alternatives to conventional remediation techniques by employing plant species capable of extracting and stabilizing pollutants. This study assesses the potential of Cannabis sativa L. var. ‘Carmagnola’ for the remediation of Pb, Cr, Cu, and Ni from four different growth substrates. This species was selected for its high biomass yield, tolerance to toxic environments, and capacity for heavy metal accumulation. Experimental results showed that the composition of the growing substrate significantly affected HM uptake, with higher accumulation occurring in less compact mixed substrates. HM removal from contaminated growth substrates varied between 55 and 75% for Cr, 60–78% for Ni, 32–86% for Cu and 43–84% for Pb after four months of growth in a greenhouse environment. In addition to pollutant removal efficiency, the study explored thermochemical harvested biomass post-processing via pyrolysis in order to produce biochar, a material with recognized agronomic beneficial properties and positive environmental value. Biochar generated from harvested biomass after phytoremediation tests showed residual HM content lower than the applicable EU thresholds for agricultural soil amendment. Integrating bioremediation with biochar production can promote a circular bioeconomy approach to environmental restoration, by transforming contaminated residual biomass into a useful resource rather than waste. These findings support the feasibility potential of coupling C. sativa phytoremediation and biochar production as an environmentally sustainable strategy for large-scale remediation of heavy metal-contaminated soils.