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Environmental fate & pathways

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Although CAS# 756-13-8 is immiscible with water, it hydrolyzes completely when forced into contact with water to PFPA (CAS# 422-64-0) and a volatile hydrofluorocarbon (heptafluoropropane), with a half-life of <2.5 minutes.  Although the propensity for CAS #756-13-8 to go into water is extremely low, once CAS #756-13-8 is in the water phase, the rate of hydrolysis is rapid.  Therefore, CAS# 756-13-8 cannot be meaningfully examined in biodegradation assays, and we have proposed waiving of all biodegradation tests for lack of technical feasibility.  Ready biodegradability studies of PFPA demonstrated little or no biodegradation in screening tests and no toxicity to activated sludge, and we have proposed waiving of any further biodegradation tests as providing no useful information.

CAS# 756-13-8 is expected to undergo photolysis in the atmosphere, forming TFA (CAS# 76-05-1), HF (CAS# 7664-39-3) and carbon dioxide; PFPA may also be formed photolytically under certain, NOx-limited conditions.   A review of available information indicates that TFA under aerobic conditions is not readily or inherently biodegradable.  It appears possible that there could be some biodegradation of TFA in the environment, particularly under anaerobic conditions.  However, while there is some evidence of defluorination and decarboxylation of TFA in a few laboratory studies, these data are inconclusive and the rates at which biodegradation could potentially occur in natural environments would be expect to be very low to negligible.   To date, no evidence of hydrolysis and photolysis of TFA has been observed in laboratory studies(1, 2, 3).  In addition, it has been shown from studies with many other longer chain perfluorinated moieties that fluorochemicals are oxidatively recalcitrant and resistant to most conventional waste treatment technologies(4).  It can be assumed TFA will remain as TFA and not degrade further under environmental conditions.  Therefore, little new information would be gained by conducting additional biodegradation/simulation studies with TFA. We propose to waive all tests pertaining to REACH Annex IX.9.2 for TFA.  HF is an inorganic substance and therefore biodegradation studies do not need to be conducted.

 

References

1) Boutonnet (Ed)., 1999.  Environmental Risk Assessment of Trifluoroacetic Acid.  Human and Ecological Risk Assessment:  Vol. 5, No. 1, pp. 59-124.

2) Benesch, J. A., M. S.  Gustin, G. R. Cramber and T. M. Cahill, 2002.  Investigation of effects of trifluoroacetate on vernal pool ecosystems.  Environmental Toxicology and Chemistry, Vol. 21, No. 3, pp. 640-647

3) Ellis et al.  2001.  The fate and persistence of trifluoroacetic and chloroacetic acids in pond waters.  Chemosphere 42 (2001) 309-318

4) Vecitis, C. D., H. Park, J. Cheng, B. T. Mader and M. R. Hoffmann, 2009. Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Frontiers Environ. Sci. Eng. China Vol. 3, No. 2, pp. 129 -151