Chronic toxicity of lithium to the fingernail clam <i>Pisidium dubium</i> and the water flea <i>Daphnia pulex</i>

Lithium (Li) is used in batteries and pharmaceutical applications. The growing use raises concerns about impacts on aquatic ecosystems and the need for better source management. The study objective was to investigate Li chronic toxicity and bioaccumulation using two native freshwater species to allow water quality guideline derivation. We conducted toxicity tests in which the fingernail clam Pisidium dubium (28-day exposure) and the water flea Daphnia pulex (21-day exposure) were exposed to a control and six environmentally relevant nominal concentrations of Li ranging from 0.05 to 10 mg/L and 0.5 to 3 mg/L Li, respectively. Solubility and partitioning tests indicated that Li readily dissolved in water and did not sorb onto particles as filtered and unfiltered Li concentrations were similar. Results for Pisidium dubium revealed that Li exposure affected burrowing (EC50 = 1.59 mg/L, EC10 = 0.99 mg/L) and survival (LC50 = 1.37 mg/L, LC10 = 0.77 mg/L). Soft tissue Li content in Pisidium dubium was similar across all exposures at the end of the tests suggesting clams control internal Li concentrations despite increased exposure. Daphnia pulex was less sensitive to Li than P. dubium since Li exposure affected reproduction (EC50 = 1.77 mg/L, EC10 = 1.42 mg/L) and somatic growth based on body size changes (EC50 = 3.01 mg/L, EC10 = 1.97 mg/L). Updated species sensitivity distribution using our new data suggests a Li water quality guideline of 0.034 mg/L. This value falls within the range of Li concentrations near contaminated areas, underscoring the need for adequate controls to mitigate ecological risk. Future research should better characterize how Na, Ca, and pH influence Li toxicity at both the organismal and molecular levels.