Hemp flowers cultivated on a soil contaminated with cadmium, lead and zinc exhibit valorization potential

Industrial hemp (Cannabis sativa L.) is an effective crop for the phytomanagement of lands contaminated with trace metals, demonstrating tolerance to metal toxicity without significant impacts on its value-chain. However, the effects of metal contamination on hemp flowers remain understudied, limiting the assessment of the valorization potential for this valuable plant part. In a greenhouse experiment, we evaluated flower production, cannabinoid content and metal accumulation in hemp grown on a soil contaminated with Cd, Pb and Zn (pseudo-total concentrations: 13.0, 664 and 1048 mg kg^-1, respectively). Our results suggest a limited capacity for phytoextraction, with low removal rates for all three metals. Still, hemp flowers presented favorable features that support valorization potential. Both flower biomass and the synthesis of cannabidiol and tetrahydrocannabinol were comparable to plants grown under reference conditions. Notably, inflorescences exhibited the lowest accumulation of Cd and Pb among all plant tissues. Concentrations for these elements were 0.45 and 1.1 mg kg^-1 respectively, remaining below most commercial limits for herbal drug products. These findings demonstrate that hemp flowers can be safely produced on metal-contaminated soils, reinforcing the suitability of hemp as a robust and versatile crop for the phytomanagement of legacy metal pollution.