Use of Biochar and Industrial Hemp for Remediation of Heavy-Metal-Contaminated Soil: Root Uptake and Translocations for Cd, Pb, and Zn

Phytoremediation has been reported as a more energy-efficient, and therefore cost-effective, method of environmental restoration compared to traditional remediation methods for heavy-metal-contaminated soils. Biochar has been shown to have variable effects on remediation potential in heavy-metal-contaminated soils. The objective of this study was to evaluate the effects of soil contamination level (i.e., low, medium, and high), industrial hemp (Cannabis sativa L.) cultivar (i.e., ‘Carmagnola’ and ‘Jinma’), biochar rate (i.e., 0, 2, 5, and 10% by volume), and their interactions on root tissue Cd, Pb, and Zn concentrations and uptakes; whole-plant Cd, Pb, and Zn uptakes; and translocation factors after 90 days of hemp growth in contaminated soil from the Tar Creek Superfund Site near Picher, Oklahoma. Hemp removal of Cd, Pb, and Zn differed between soil contamination levels (p < 0.01), but was unaffected (p > 0.05) by the hemp cultivar or biochar rate, except for total Zn uptake. Total Zn uptake was affected (p = 0.02) by the biochar rate in the medium- and high-contaminated soils, where total plant Zn uptake in the high-contaminated soil was numerically the largest with 10% biochar (0.28 mg cm−2) and in the medium-contaminated soil was numerically the largest with 2% biochar (0.07 mg cm−2), but was unaffected (p > 0.05) by the biochar rate in the low-contaminated soil. The translocation factor for Zn uptake in the low and medium soils was >1, indicating industrial hemp as a potential Zn hyper-accumulator up to a threshold soil contamination level. Results demonstrate that biochar amendment has the potential to enhance hemp’s remediation capability of heavy-metal-contaminated soils.