Health check-up of a freshwater bivalve exposed to lithium

Lithium (Li) has become essential for energy and digital transitions, especially as a component of rechargeable batteries. Its growing uses worldwide lead to increasing anthropogenic releases of Li into the environment, which is making Li as an emerging contaminant. It is thus critical to evaluate the ecotoxicological impact of Li, which has been poorly studied unlike its human toxicology. The objectives of this work were to assess the potential adverse effects of Li on aquatic ecosystems. Bioaccumulation and potential sublethal effects (at individual and cellular levels) of Li have been investigated in the widespread and ecologically relevant freshwater bivalve Dreissena polymorpha. To tackle these issues, mussels were exposed to several spiking of 40, 100 and 250 μg Li L^-1 for 28 days to reproduce anthropogenic contamination scenario. Results demonstrated that bivalves significantly accumulated Li in a dose-dependent manner, from 2 to 10 μg g^-1 dry weight (bioaccumulation factor, BAF ≈ 19 L kg^-1). Bioaccumulation of Li reached a steady-state from seven days of exposure and BAF values were constant regardless the exposure concentration indicating a tight regulation of Li body burden. Lithium exposure leads to increased energy demand associated with a higher lactate dehydrogenase activity and the decrease of protein concentrations. The observed weight gain, increased cellular metabolism, decreased apoptosis, induction of antioxidant defenses and cation content modification in D. polymorpha were also reported in previous studies on humans. The observed effects intensified with exposure concentration and duration, which implies an increased risk for aquatic organisms exposed to Li chronic contamination. Overall, the present study provides new knowledge concerning the impact of Li on non-targeted species, which have implications for the environmental risk assessment of Li in freshwater ecosystems. It also open new perspectives for the understanding of Li toxicokinetics and toxicodynamics on freshwater organisms.