Integration of responses to lithium in mussels at different levels of biological complexity.

The increasing use of lithium (Li) in modern technology and medicine has raised up concerns in the scientific community due to the potential impact of this metal on the aquatic environment. Although several effects have been reported in different organisms, there is still scarce information concerning the mechanisms and chronic effects of Li toxicity in marine life. Our main objective is to determine biological effects of sub-lethal concentrations in Mytilus galloprovincialis at different biological organization levels using the biomarker approach. Mussels were exposed to environmental Li concentrations: 0.1, 1 and 10 mg/L. Samples of gills, muscle and digestive gland were taken at days 1, 7 and 21 for the assessment of biochemical, histochemical and histological endpoints. Results showed that exposure to Li caused greater impacts in a dose and time-dependent manner at different biological organization levels. Changes in acetylcholinesterase (AChE) activity were detected at day 1 (induction) and day 21 (inhibition) in accordance with increasing Li levels, indicating possible neurotoxic effects, while catalase (CAT) inhibition, and subsequent induction, was detected at day 1 in proportion to Li concentrations. Lysosomal biomarkers demonstrated a decreasing lysosomal membrane stability with higher Li doses after 21 days of exposure, whereas 10 mg Li/L provoked lysosomal size reduction from day 1. Finally, the integration of these biological responses into an IBR index indicated a clear effect of exposure after 21 days in a dose-dependent way, leading to cellular and tissue damage as consequence. Moreover, a time-course response was observed with an enhanced oxidative stress at day 1, and a neurotoxic effect, lysosomal membrane destabilization and histopathological alterations after 7 and 21 days of exposure to medium and high Li concentrations. Consequently, these findings provide valuable insights into Li's effects on marine life, emphasizing the need for further long-term studies across different biological organization levels.