Multigenerational ecotoxicity of tris(2-butoxyethyl) phosphate to the tropical water flea Ceriodaphnia cornuta and probabilistic ecological risk assessment in freshwater environments

The widespread use of the organophosphorus flame retardant tris(2-butoxyethyl) phosphate (TBOEP) and its presence in aquatic environments pose a hazard to wildlife. This study investigates the chronic ecotoxicity of TBOEP at environmentally relevant concentrations (6 ± 0.7 µg L⁻¹) in the tropical water flea Ceriodaphnia cornuta over seven generations. Delayed toxicity emerged from the second generation (F1) to the fourth generation (F3), affecting survival, body length, and fertility. Recovery occurred in F4, followed by complete inhibition in F5 and F6, where no organisms survived beyond day 10. Population dynamics revealed minimal growth in F5, leading to extinction by F6. This is the first study to demonstrate the multigenerational lethal effects of TBOEP at environmentally relevant concentrations, highlighting ecological threats to C. cornuta and other sensitive species. The mechanisms underlying these effects remain unclear and require sub-organismal investigation. The chronic predicted no-effect concentration, estimated at 8.64 µg L⁻¹, exceeds the tested concentration and therefore may not adequately protect vulnerable species. Ecological risk assessments based on TBOEP concentrations detected in surface waters since 2014 suggest potential risks at elevated levels in specific locations across multiple countries. Additional research is essential to validate TBOEP's toxicity across species under chronic and multigenerational exposure. Current ecological risk assessments likely underestimate TBOEP's threat to aquatic ecosystems, emphasizing the need for reassessment to better safeguard biodiversity.