Comparing the acute and chronic toxicity of flupyradifurone and imidacloprid to non-target aquatic arthropod species

Flupyradifurone (FPF) is a new type of butenolide insecticide. It was launched on the market in 2015 and is considered an alternative to the widely used neonicotinoids, like imidacloprid (IMI), some of which are banned from outdoor use in the European Union. FPF is claimed to be safe for bees, but its safety for aquatic organisms is unknown. Its high water solubility, persistence in the environment, and potential large-scale use make it urgent to evaluate possible impacts on aquatic systems. The current study assessed the acute and chronic toxicity of FPF for aquatic arthropod species and compared these results with those of imidacloprid. Besides, toxicokinetics and toxicokinetic-toxicodynamic models were used to understand the mechanisms of the toxicity of FPF. The present study results showed that organisms take up FPF slower than IMI and eliminate it faster. In addition, the hazardous concentration 5th percentiles (HC05) value of FPF derived from a species sensitivity distribution (SSD) based on acute toxicity was found to be 0.052 µmol/L (corresponding to 15 µg/L), which was 37 times higher than IMI (0.0014 µmol/L, corresponding to 0.36 µg/L). The chronic 28 days EC10 of FPF for Cloeon dipterum and Gammarus pulex were 7.5 µg/L and 2.9 µg/L, respectively. For G. pulex, after 28 days of exposure, the no observed effect concentration (NOEC) of FPF for food consumption was 0.3 µg/L. A toxicokinetic-toxicodynamic (TKTD) model parameterised on the acute toxicity data well predicted the observed chronic effects of FPF on G. pulex, indicating that toxicity mechanisms of FPF did not change with prolonged exposure time, which is not the case for IMI.