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EC number: 436-710-6 | CAS number: 756-13-8
CAS# 756-13-8 is a completely fluorinated ketone. The substance is a liquid at room temperature with a high vapor pressure (40 kPa at 25°C). The water solubility of CAS# 756-13-8 cannot be measured owing to its extremely short half life at all pH values measured. Most releases of CAS# 756-13-8 are expected to be atmospheric emissions based upon its intended uses. Fugitive emissions may occur at transfer points. During routine use, there is no anticipated release to water or wastewater in the EU. Therefore, this compound will remain in the atmosphere when released from industrial applications. The most important fate process, by a factor of 6000-120,000, is expected to be direct photolysis of CAS# 756-13-8. A reasonable initial step (scission of the chemical into perfluoropropionyl and isopropyl radicals) and experimental data on the fate of perfluorinated radicals suggest that the ultimate degradation products are hydrofluoric acid (HF, CAS# 7664-39-3), trifluoroacetic acid (TFA, CAS# 76-05-1) and CO2 under high nitric oxide (NO) concentrations, with perfluoropropionic acid (PFPA, CAS# 422-64-0) also formed under NO-free conditions. Hydrolysis of CAS# 756-13-8 to PFPA and 1,1,1,2,3,3,3-heptafluoropropane (HFP), while intrinsically rapid, has been assessed as a negligible factor (by the same factor of 6000-120,000) in atmospheric water droplets. The relative unimportance was due mostly to scarcity of liquid water droplets vis-à-vis sunlight in the troposphere. The primary degradation products, TFA and HF, and the negligible amount of PFPA formed in the atmosphere are miscible in water and are completely ionized in rainwater. They are expected to undergo wet deposition with no further significant transformation. Please note that a published environmental risk assessment on TFA is available in the literature(1).
CAS# 756-13-8 is not expected to partition to soils or surface waters. Upon accidental direct release of CAS# 756-13-8 to the aquatic compartment, CAS# 756-13-8 is expected to hydrolyze to PFPA and HFP with a half-life <2.5 minutes. Therefore, biodegradation and bioconcentration tests are not applicable for the parent compound. CAS# 756-13-8 has an estimated log Kow of 5.48, and therefore the bioaccumulation potential must be addressed. However, given its extremely short half-life due to hydrolysis, CAS# 756-13-8 will not exist in aquatic environments or organisms for a sufficient time to allow partitioning into lipid tissues or testing of bioconcentration meaningfully, and therefore this chemical is not expected to bioaccumulate in aquatic organisms. Further, its short hydrolytic half-life indicates CAS# 756-13-8 will degrade abiotically before biodegradation can occur in aquatic or terrestrial systems. For substances that hydrolyse that quickly (<10 hr) BCF and biodegradation for the hydrolysis products have to be assessed. Biodegradation and bioaccumulation can therefore be discussed in the context of the degradation products, predominantly acids resulting from photolysis in the atmosphere. As CAS# 756-13-8 is a perfluorinated chemical, global warming and ozone depletion potentials may be of interest. Global warming potential depends on three factors: absorption of infrared radiation, area of the spectrum the absorption occurs and lifetime of the material in the atmosphere. D’Anna et al.(2), measured both the integrated area and the atmospheric lifetime of the material. The conclusion with respect to global warming potential was "Although the integrated absorption cross section of PFMP is large, the short atmospheric lifetime makes the global warming potential of the compound negligible." CAS# 756-13-8 has been shown not to react with ozone(3). Although degradation products include a variety of species that release free fluorine radicals, radicals do not contribute to ozone depletion because of fast quenching of F* by water or hydrogen donors, slow reaction of FO* radicals with oxygen, and obligate reformation of F* in the pathway(4). F* radicals are rapidly and irreversibly removed from the atmosphere after quenching as HF. It is therefore concluded that CAS# 756-13-8 does not contribute to ozone depletion.
The formation of HFP in the atmosphere is negligible. It is a highly volatile gas (vapor pressure = 3410 mmHg (454.6 kPa) at 25°C) of low water solubility, and will remain entirely in the atmospheric compartment. No exposure to terrestrial or aquatic organisms is expected. HFP is subject to indirect photolysis with an estimated atmospheric lifetime of 34.2 years, forming TFA, HF and CO2(5).
Partitioning of HF, TFA and PFPA in the environment is driven by the fact that these acids are completely ionized at environmental pH values, are miscible in water, and are not likely to bind with organic matter based on low Koc values and low log Kow values. HF, TFA and PFPA will be associated with the aqueous phase of any environment where they are released, and will be highly mobile in soils. HF, TFA and PFPA that have deposited in aquatic compartments are expected to remain in the aquatic compartment.
The notifier has assessed PFPA in ready biodegradation tests and demonstrated that essentially no biodegradation occurs. PFPA is not expected to biodegrade in surface waters, sediments or soils. The sponsor completed a bioconcentration study of PFPA in carp. The BCF at steady state was found to be 1.2 and < 4.8 at the two exposure concentrations. The lack of bioaccumulation potential is further evidenced by the estimated octanol/water partition coefficient. At environmentally relevant pH, PFPA will be totally ionized and is predicted to have a log Kow of -1.33 as predicted by QSAR software (Advanced Chemistry Development, Inc. (ACD/Labs) Toronto, Ontario, Canada. Version 12). Therefore PFPA is not expected to bioaccumulate in aquatic organisms.
A review of available literature indicates that TFA is not readily biodegradable and would be considered very persistent in the environment(1). TFA is very water soluble (> 10 g/mL(1)). As a water soluble anion, it is not expected to bioconcentrate in aquatic organisms. A calculated log Kow value of -2.1(1) has been proposed. BCF data was available only for terrestrial plants. At concentrations at or below the no effect level of 1 mg/L, literature bioconcentration factors ranged from 5.4 to 27(1).
1) Boutonnet (Ed.), 1999. Environmental Risk Assessment of Trifluoroacetic Acid. Human and Ecological Risk Assessment: Vol. 5, No. 1, pp. 59-124.
2) B. D'Anna, S. R. Sellevåg, K. Wirtz, and C. J. Nielsen. 2005. Photolysis Study of Perfluoro-2-methyl-3-pentanone under Natural Sunlight Conditions. Environ. Sci. Technol. Vol. 39 No. 22, pp. 8708–8711
3) N. Taniguchi, T. J. Wallington, M. D. Hurley, A. G. Guschin, L. T. Molina, and M. J. Molina. 2003. Atmospheric Chemistry of C2F5C(O)CF(CF3)2: Photolysis and Reaction with Cl Atoms, OH Radicals, and Ozone. J. Phys. Chem. A Vol. 107, No. 15, pp. 2674-2679
4) A.J. Colussi and M.A. Crela. 1994. Rate of the reaction between oxygen monofluoride and ozone. Implications for the atmospheric role of fluorine. Chem. Phys. Lett. Vol. 229, pp. 134-138
5) Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
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