Industrialization has left large surfaces of contaminated soils, which may act as a source of pollution for contiguous ecosystems, either terrestrial or aquatic. When polluted sites are recolonized by plants, dispersion of leaf litter might represent a non-negligible source of contaminants, especially metals. To evaluate the risks associated to contaminated leaf litter dispersion in aquatic ecosystems, we first measured the dynamics of metal loss from leaf litter during a 48-h experimental leaching. We used aspen (Populus tremula L.), a common tree species on these polluted sites, and collected leaf litter on three polluted sites (settling pond of a former steel mill) and three control sites situated in the same geographic area. Then, toxicity tests were carried out on individuals of a key detritivore species widely used in ecotoxicology tests, Gammarus fossarum (Crustacea, Amphipoda), with uncontaminated and contaminated leaf litter leachates, using a battery of biomarkers selected for their sensitivity to metallic stress. Leaf litters collected on polluted sites exhibited not only significantly higher cadmium and zinc concentrations but also lower lignin contents. All leaf litters released high amounts of chemical elements during the leaching process, especially potassium and magnesium, and, in a lesser extent, phosphorus, calcium, and trace metals (copper, cadmium, and zinc but not lead). Toxicity tests revealed that the most important toxic effects measured on G. fossarum were due to leaf litter leachates by themselves, whatever the origin of litter (from polluted or control sites), confirming the toxicity of such substances, probably due to their high content in phenolic compounds. Small additional toxic effects of leachates from contaminated leaf litters were only evidenced on gammarid lipid peroxidation, indicating that contaminated leaf litter leachates might be slightly more toxic than uncontaminated ones, but in a very reduced manner. Further studies will be required to verify if these patterns are generalizable to other species and to investigate the effects of contaminated leaf litter ingestion by consumers on aquatic food webs. Nevertheless, our results do not permit to exclude potential chronic effects of an exposure to contaminated leaf litter leachates in aquatic ecosystems.

This constitutes the first study to report on the reduction in toxicity of the dinoflagellate algal toxin okadaic acid after novel pulsed light (PL) treatments where ecotoxicological assessment was performed using a miniaturised format of the conventional in vivo freshwater crustacean Daphnia sp. acute toxicity test. Bivalves accumulate this toxin, which can then enter the human food chain causing deleterious health effects such as diarrhetic shellfish poisoning. This miniaturised toxicological bioassay used substantially less sample volume and chemical reagents. Findings revealed a 24-h EC₅₀ of 25.87 μg/L for PL-treated okadaic acid at a UV dose of 12.98 μJ/cm² compared to a 24-h EC₅₀ of 1.68 μg/L for the untreated okadaic acid control, suggesting a 15-fold reduction in toxicity to Daphnia pulex. The bioassay was validated in this study and correlated well with the “classic” ISO format (r = 0.98) using the traditional reference chemical potassium dichromate (K₂Cr₂O₇). Reduction by up to 65% in PL-treated okadaic acid concentration was confirmed by LC-MS/MS analysis. Findings from this study have positive ecological, societal and enterprise implications, such as the development of PL technology for the prevention or reduce algal contamination of fisheries and aquaculture industries.