Butanamine, N,N-dibutyl-, branched and linear, fluorinated

Short-term toxicity to fish

Description of key information

PTBA is not expected to be toxic to fish at the limit of solubility (0.710 µg/L) by readacross from category members.  When other category members were, tested, no toxicity was observed to fish in tests conducted with nominal concentrations ranging from 100 to 2700 mg/L.  These category member results are considered applicable to PTBA.

Additional information

PTBA is the least water soluble member of the Perfluorinated Organic Chemicals, C5-C18 category. Because these substances exhibit similarity in their physicochemical properties and toxicological properties in mammals, and because available data indicates that parent molecules are not reactive toward biological molecules and cannot undergo bioactivation by normal enzymatic processes, they can be considered members of a chemical category. Data gaps for ecological toxicity can therefore be addressed by read-across and/or trend analysis between category members. An LC50 >1000 for PTBA was reported for P. promelas in a study which was deemed unreliable. However, two reliable studies are available for other category members. Perfluoro-N-C1,3-alkyl morpholines (FC-770) was tested using D. rerio. After 96-hours, no toxicity was observed from a water-soluble fraction prepared at 100 mg/L. The mean measured concentration during the test was 0.096 mg/L. Perfluoro-C6,8-furans, pyrans and acyclic ethers (FC-77) was tested using P. promelas. In this case, test chambers were prepared at an initial loading rate of 1000 mg/L. Exposure concentrations were not measured, however, the test material could not be entirely dissolved and was observed in the test chambers throughout the experiment. No toxicity was observed. Other category members had study reports which were less detailed but were suitable for weight of evidence in the aggregate. These category members were not toxic to fish in limit tests with nominal concentrations ranging from 750 to 2700 mg/L. The analytically determined concentrations for FC-770 are not reasonable to use for readacross since FC-770 solubility is substantially higher than that of PTBA. Lack of toxicity at the limit of solubility is read across qualitatively to PTBA. The solubility of PTBA was determined to be 0.710 µg/L in organism-free Daphnia medium controls during the short-term toxicity test. This value is greater than the measured PTBA solubility in water (<0.06 µg/L) but less than the analytically determined concentrations in medium containing live daphnids. The organism-free medium solubility value is understood to be better representative of PTBA solubility in natural waters, and avoids potential impacts on the analytical result by the action of living organisms. Therefore, 0.710 µg/L is accepted as the basis for estimating the highest possible exposure concentration of PTBA in order to define the LC50.

Please see IUCLID section 13 for the category justification and a matrix of aquatic toxicity data for members of the Perfluorinated Organic Chemicals C5-C18 category.