To limit anthropogenic impact on ecosystems, regulations have been implemented along with global awareness that human activities were harmful to the environment. Ecotoxicological risk assessment is the main process which allows to assess the toxicity potential of contaminants, through different steps of laboratory testing. This process evolves along with scientific knowledge, to better predict the impact on an ecosystem. In this paper we address the importance of intraspecific variability as a potential source of error in the laboratory evaluation of harmfulness of pollutants. To answer this question, three aquatic macrophyte species with different life-history traits were chosen to cover the main life-forms found in aquatic ecosystems, Lemna minor and Myriophyllum spicatum, two OECD model species, and Ceratophyllum demersum. For each species, three or four genotypes were exposed to 7-8 copper concentrations. To assess species sensitivity, growth-related endpoints such as Relative Growth Rate (RGR), based either on biomass production or on length/frond production, and chlorophyll fluorescence Fv:Fm, were measured. For each endpoint, EC50 was calculated. Our results showed that all endpoints were affected by Cu exposure, Fv:Fm of M. spicatum excepted, and significant differences were found among genotypes in terms of Cu sensitivity. L. minor sensitivity to Cu significantly varied for Fv:Fm, which showed up to 35 % of variation in EC50 values among genotypes. Significant differences in EC50 values were found for RGR based on length for M. spicatum, with up to 72% of variation. Finally, C. demersum demonstrated significant sensitivity differences among genotypes with up to 78 % variation for EC50 based on length. Overall, interspecific variation was higher than intraspecific variation, and explained 77% of the variation found among genotypes for RGR based on biomass, and 99% of the variation found for Fv:Fm. Our results highlight that depending on the endpoint, sensitivity can vary greatly within a species, and not all endpoints should be considered relevant in risk assessment.
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