First evidence of lithium toxicity in the cryptic species complex of the estuarine copepod Eurytemora affinis.

The development of renewable and low-carbon energy sources means that strategic elements such as lithium (Li) are increasingly being used. The data available on the effects of Li on aquatic organisms are relatively scarce. The copepod Eurytemora affinis, widely distributed in the brackish estuarine waters of the northern hemisphere, is a species of choice in ecotoxicology but in fact constitutes a cryptic species complex, composed of at least six cryptic species. Cryptic diversity can lead to misinterpretation and alter the reproducibility of routine ecotoxicological tests. In the present study, two cryptic species of the E. affinis complex from the Seine (European clade) and the St. Lawrence (North-Atlantic clade) estuaries were used to assess Li toxicity and to compare their differential sensitivity. Larvae were exposed to different concentrations of Li (0.4, 4.39, 35.36 and 80.83 mg L-1) under semi-static conditions for 96 h. Larval development stages were determined and log-logistic functions were fitted to evaluate mortality (LC50) and growth (EC50) parameters. After 96 h of exposure, the results showed that the European and North-Atlantic clades had LC50 values of 55.33 and 67.81 mg L-1 and EC50 values of 28.94 and 41.45 mg L-1, respectively. A moderate difference in sensitivity to Li between the European and North-Atlantic clades of the E. affinis complex was observed. Thus, the cryptic species diversity should be considered using E. affinis to avoid bias in the interpretation of the data. Despite environmental concentrations of Li are expected to increase over the next years, EC50 and LC50 found for E. affinis cryptic species are largely higher than Li environmental concentrations to provoke extreme effects.

Advancing environmental monitoring across the water continuum combining biomarker analysis in multiple sentinel species: A case study in the Seine-Normandie Basin (France).

Nowadays, biomarkers are recognized as valuable tools to complement chemical and ecological assessments in biomonitoring programs. They provide insights into the effects of contaminant exposures on individuals and establish connections between environmental pressure and biological response at higher levels. In the last decade, strong improvements in the design of experimental protocols and the result interpretation facilitated the use of biomarker across wide geographical areas, including aquatic continua. Notably, the statistical establishment of reference values and thresholds enabled the discrimination of contamination effects in environmental conditions, allowed interspecies comparisons, and eliminated the need of a reference site. The aim of this work was to study freshwater-estuarine-coastal water continua by applying biomarker measurements in multi-species caged organisms. During two campaigns, eight sentinel species, encompassing fish, mollusks, and crustaceans, were deployed to cover 25 sites from rivers to the sea. As much as possible, a common methodology was employed for biomarker measurements (DNA damage and phagocytosis efficiency) and data interpretation based on guidelines established using reference values and induction/inhibition thresholds (establishment of three effect levels). The methodology was successfully implemented and allowed us to assess the environmental quality. Employing multiple species per site enhances confidence in observed trends. The results highlight the feasibility of integrating biomarker-based environmental monitoring programs across a continuum scale. Biomarker results align with Water Framework Directive indicators in cases of poor site quality. Additionally, when discrepancies arise between chemical and ecological statuses, biomarker findings offer a comprehensive perspective to elucidate the disparities. Presented as a pilot project, this work contributes to gain insights into current biomonitoring needs, providing new questions and perspectives.