The toxicity of fluorotelomer acids to freshwater organisms and a preliminary evaluation of mechanism of action
The saturated and unsaturated fluorotelomer carboxylic acids (FTCA and FTuCAs, respectively) have been identified as dominant metabolites in the degradation pathway of fluorotelomer alcohols (FTOHs) to the perfluorinated carboxylic acids (PFCAs). Due to their relatively low volatility and high solubility, it is expected that the FTCAs will be deposited into surface waters via precipitation events. Toxicity of the 6, 8 and 10:2 FTCAs and FTuCAs to aquatic invertebrate (survival and growth) and algal species (growth) was investigated; results followed a general trend of increasing toxicity with increasing chain lengths and saturation. Acute EC50 values ranged from 3.87 mg/L for the 10:2 FTuCA to 'Chlorella vulgaris', to >100 mg/L for the 6:2 FTuCA for 'Pseudokirchneriella subcapitata '. Acute LC50 values ranged from 3.70 mg/L for the 10:2 FTuCA to >100 mg/L for the 6:2 FTuCA to 'Hyalella azteca'. The first vertebrate toxicity assay with the 10:2 FTCA, in the zebra fish ' Danio rerio', showed decreased reproduction at exposure levels as low as 317 [mu]g/L, and significantly increased liver somatic indices in concentrations as low as 4.9 g/L. In addition to this, extraction of tissue showed high bioconcentration rates, and the presence of several metabolites (10:2 FTCA, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFUdA), including the 9:3 FTCA, which heretofore have not been observed, and was not present in the exposure solutions. A frog embryo teratogenesis assay --'Xenopus' (FETAX) was conducted in an attempt to elucidate the toxic mode of action the FTCAs. Individual evaluation of the parent FTCA and each metabolite resulted in mortality in only the hydrofluoric acid (HF) treatment, suggesting that HF plays major role in FTCA toxicity. Total glutathione was monitored in the FETAX assay, and each metabolite had increased anti-oxidant activities relative to the control. While the FTCAs seem to maintain their increased toxicity to vertebrates relative to the PFCAs, effect concentrations are well above those detected in the environment and it is concluded that they presently pose negligible risk to aquatic receptors.