3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-(trifluoromethyl)-hexane

Bioaccumulation: aquatic / sediment

Description of key information

The BCF of CAS# 297730-93-9 in fish was reported in two unreliable studies.  However, owing to the low water solubility, high vapor pressure, and high measured Henry’s Law constant of this substance, no exposure to aquatic organisms is expected.  The degradation product PFBA is not expected to bioaccumulate based on very low dissociation constant (pKa = 0.40), ionization at pH 7, and estimated log pH-specific partition coefficient (log D) of -0.36 at pH 7.

Additional information

The bioconcentration factor of CAS# 297730-93-9 in Carp fish (Cyprinius carpio), was assessed in two studies based on OECD TG305. Due to its low water solubility, both studies used a hydrogenated castor oil ethoxylate dispersant (1:20 ratio with test substance) and a 2-methoxyethanol cosolvent to maintain CAS# 297730-93-9 in solution. In one study, fish were exposed to CAS# 297730-93-9 at 50 µg/L and 500 µg/L (reported as 0.05 and 0.5 µg/mL) for 70 days. CAS# 297730-93-9 was dispersed with 1.0 or 10 mg/L HCO-30 (30 moles ethoxylated) and 0.024 mL/L or 0.015 mL/L 2-methoxyethanol (final concentrations in test chambers). After day 70, administration was halted and depuration was monitored for 42 days.  No sublethal effects were observed in the test groups. Concentration of CAS# 297730-93-9 in fish tissues reached steady state by day 28. BCF ranges measured in this study were 3150-8530 for the low exposure concentration and 287-1020 for the high exposure concentration (average values were 6200 and 920, respectively). Depuration half lives were 39 and 35 days, respectively.

 

In the other study, fish were exposed to CAS# 297730-93-9 at 4.61 µg/L for 56 days. CAS# 297730-93-9 was dispersed with 0.1 mg/L HCO-20 (20 moles ethoxylated) and 0.4 µL/L 2-methoxyethanol (final concentrations in test chambers). After day 56, administration was halted and depuration was monitored for 36 days.  No sublethal effects were observed in the test groups. Concentration of CAS# 297730-93-9 in fish tissues reached steady state by day 35. The average BCF reported in this study was 5200, with a range of 4600-6000. Depuration half life was 10.8 days. The second study's results are similar to those of the first study, but provide a less conservative assessment of bioconcentration and depuration than the results of the first study.

 

Due to the very low water solubility of CAS# 297730-93-9 (21.3 µg/L), the studies made use of both a cosolvent and a dispersant to maintain substance concentration during the test. The test guideline specifically names several surfactants, among them HCO-40 (ethoxylated hydrogenated castor oil). HCO-20 and HCO-30 are not listed in the method, however these differ from HCO-40 only in degree of ethoxylation. 2-methoxyethanol is also permitted under OECD TG305. The amounts used in the two studies are well within the method recommendation that solubilising agent concentration not exceed 100 µL/L. OECD TG305 discourages use of either cosolvents or dispersants in bioconcentration testing. These studies use both, which is highly irregular. Therefore, the results of these studies are not reliable. However, this substance has a measured Henry’s Law constant of 4.7 x 10⁷ Pa m³/mol. Because of the extreme volatility of this material, it is not expected to be present in aquatic systems, and no exposure to aquatic organism is expected.

 

We have proposed waiving of testing of bioconcentration on PFBA because of its acidity (pKa = 0.40), ionization at pH 7, and estimated log pH-specific partition coefficient (log D) of -0.36 at pH 7. In addition, perfluoropentanoic acid, with a one carbon longer perfluoroalkyl chain, could not be detected in Rainbow trout blood or tissue at any time point during a bioconcentration experiment.⁽¹⁾ Perfluoropropanoic acid, with a one carbon shorter perfluoroalkyl chain, had experimental BCF values of 1.2 and ≤4.8 in a study using Carp. Because perfluoroacids bracketting PFBA in chain length do not bioaccumulate, PFBA will also not bioaccumulate in aquatic organisms.

1) Martin JW, SA Mabury, KR Solomon, DCG Muir. 2003. Bioconcentration and tissue distribution of perfluorinated acids in rainbow trout (Oncorhynchus mykiss). Environ. Toxicol. Chem. 22: 296 -204.