New microbioassays based on biomarkers are more sensitive to fluvial water micropollution than standard testing methods.

Recent investigations suggest that, despite lack of lethality in validated bioassays, micropollutants in surface waters could induce sublethal toxicity in sensitive taxa, jeopardizing their biological performance and eventually leading to populations' extinction. A broader array of testing species, the miniaturization of bioassays and the development of reliable biomarkers of damage are sought in order to improve ecological relevance and cost efficiency of environmental monitoring. Our aim is to assess the different sensitivity of validated bioassays and new approaches using biomarkers as sensitive endpoints of toxicity in spores of Polystichum setiferum and Danio rerio embryos. Six water samples were collected in Tagus basin in summer and winter. Samples tested induce no acute toxicity in validated methods (algae growth inhibition and daphnia mobility inhibition). Summer water samples induced acute membrane damage (lipid peroxidation) in Danio rerio embryos and hormetic increases in fern spore mitochondrial activity. One of the samples dramatically reduced mitochondrial activity indicating severe acute sublethal phytotoxicity. All the winter samples induced significant decreases in fern spore mitochondrial activity and membrane damage increases in Danio rerio embryo. Furthermore, three samples induced lethal phytotoxicity in fern spores. We conclude that the new microbioassays show a better sensitivity to fluvial water micropollution and confirm the necessity to test critical life stages such as development and provide cost-efficient methods for environmental monitoring.