Lithium (Li) Accumulation and Toxicity Assessment in Hemp (Cannabis sativa L.) Plants by Biometric, Physiological and Ionomic Analyses Under Hydroponics

Lithium is a metal of particular interest due to its growing industrial use. However, concerns have been raised about its potential impact on the environment. A notable demand for sustainable technologies to remove Li from environmental matrices and possibly recover it for re-utilization is occurring. Plants can be successfully targeted for this purpose, but further research is needed to expand knowledge. In this regard, laboratory studies under full control of the parameters affecting plant performances are very helpful to obtain insight on the matter. This study investigated the potential of hemp (Cannabis sativa L.) plants to tolerate and accumulate Li in their organs under hydroponic conditions, evaluating morphological, physiological and ionomic parameters. Hemp plants were exposed for 10 days to different LiCl concentrations (0, 50, 150 and 300 mg L−1). The results show the toxicity of the metal at the highest concentration tested (150 and 300 mg L−1 LiCl), causing a reduction in biomass and pigment content (evaluated by spectral reflectance), as well as an uneven impairment of the photosynthetic processes across the leaf lamina (highlighted by the imaging of chlorophyll fluorescence). The ionomic analysis revealed the increase in some micronutrients (Na, Mn, Zn, Mo and Co), which may be involved in the plant’s response to stress conditions at the highest tested Li concentration. Despite accumulating up to 500 mg kg−1 of Li in their aerial organs, hemp plants exposed to 50 mg L−1 LiCl did not exhibit any toxic effects at biometric and physiological levels. These results open up interesting perspectives for the use of this plant species for phytoremediation and metal recovery from biomass, in line with the EU regulations requiring environmentally sustainable practices.