Experimental approach for evaluating the ability of hemp (Cannabis sativa L.) to tolerate and phytoextract lithium from environmental matrices

Lithium is a soft, silvery-white, alkaline metal. It is the lightest element in the first group of the periodic table and generally the lightest of the metals, with a density of (0.534 g cm-3).The economic importance of Li has grown exponentially over time, and this metal now plays a significant role in the global economy, mainly due to the growing demand for Li-ion batteries, which are widely used to power electric vehicles, electronic devices and to store energy from renewable sources [1].Lithium is currently considered one of the most worrying emerging contaminants [2] due to its high use and the possible inappropriate disposal practices, which are likely to increase its concentration in environmental matrices and its potential toxic effects on soil and aquatic organisms [3].Measures must therefore be taken to mitigate these negative effects, and nature-based technologies could be of interest for their environmental and economic sustainability.Plant-lithium interactions have recently been investigated to assess both metal toxicity [4] and the ability of plants to phytoaccumulate. To gain insight into both issues, two proof-of-concept studies were conducted under laboratory conditions to assess the ability of Cannabis sativa L. to tolerate and bioaccumulate Li added to the growth medium. To this end, an in vitro plant study and a hydroponic growth chamber experiment were carried out.Micro-shoots of C. sativa were exposed for two weeks under controlled microenvironmental conditions to 0 (control), 50 mg L-1, 150 mg L-1, 300 mg L-1 LiCl supplied by Murashige and Skoog growth medium.For the hydroponic condition, three-week-old plantlets were grown for 10 days in a growth chamber in Hoagland's solution containing 0 (control), 50 mg L-1, 150 mg L-1, 300 mg L-1 LiCl.At the end of both experiments, the plants were analysed for morpho-physiological and ionomic traits by evaluating biometric parameters, pigment content, photosynthetic performance (chlorophyll fluorescence measurements), macro- and micronutrient concentration and Li accumulation in the organs.The results demonstrate the remarkable ability of hemp plants to absorb, accumulate and translocate Li; it's particularly interesting to note the high absorption rate combined with no toxicity at the lowest concentration tested. Changes in photosynthetic performance and ion content were observed at the highest Li concentration tested. The high accumulation and translocation of lithium provide interesting future scenarios in the orbit of metal biorecovery from contaminated environmental matrices and/or natural sources at low concentrations. However, further experiments under real conditions are needed to confirm these results. Keywords: metal toxicity, lithium, hemp, environmental contamination, photosynthesis, nature-based solution, plant physiology References [1] Christmann et al., Lithium process chemistry (pp. 1-40). Elsevier 2015 [2] Melchor-Martínez et al., Chemical and Environmental Engineering 2021,3, 100104 [3] R.B. Kaunda, Journal of Energy & Natural Resources Law 2020, 38, 237-244. [4] R. Kastori, et al., Contemporary Agriculture 2022, 71, 226-239.