LAUSR

Fire retardants are commonly used for fighting wildfires. Retardant chemicals washed via runoff into aquatic systems may be concentrated, thus exposing aquatic species to high levels of ammonium, phosphate, and iron. These chemicals directly affect individual species, which can also cascade to the rest of the aquatic community. We investigated the effects of a prevalent fire retardant, FR CROS 134 (FR), at various concentrations (0 to 11.4 × 102 mg l−1) on larval fire salamander (Salamandra infraimmaculata) and aquatic community structure (bacteria, algae and invertebrates) using mesocosms. We show a negative effect of the presence of FR on the survivorship and time to metamorphosis of salamander larvae (94–17% and 48–64 days, respectively). Moreover, increasing FR concentrations were found to inhibit the predation rate of salamander larvae on mosquito larvae (89–14%). FR decreased the invertebrate community diversity with changes in composition and shifts in evenness and dominance (e.g., cladoceran species abundance increased, whereas calanoid copepod species declined). Finally, cyanobacteria and eukaryotic algal abundance increased, while heterotrophic bacterial abundance decreased with FR addition. The effects of fire retardants on biodiversity found here and the growing use of fire retardants worldwide call for additional evidence-based assessment of their impact, especially in aquatic ecosystems.