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CAS# 756-13-8 is very volatile (VP 40 kPa at 25°C). CAS# 756-13-8 is therefore expected to be present in the vapor phase in the atmosphere, from which it will be removed by direct photolysis with a half-life of approximately one week. The phototransformation products hydrofluoric acid (HF), trifluoroacetic acid (TFA), and smaller amounts of perfluoropropanoic acid (PFPA) are water soluble and dissociate rapidly in aqueous solution. These acid are not expected to be volatile, and the main removal pathway from the atmosphere is expected to be wet and dry deposition.

We have proposed waiving testing of log Koc on CAS# 756-13-8 based on adaptations to data requirements in column 2 of Annex VIII. Further, as a volatile chemical CAS# 756-13-8 is unlikely to be present in soil. Literature values of Kd for TFA ranged from <2 to 20 in various soils(1). Using a reported log Kow value of -2.10(1), a log Koc value of -1.006 was calculated using a linear free energy relationship(2) for use in further assessment. Log Koc of the transformation product PFPA was estimated by modeling using ACD/Labs software, resulting in Koc values of ca. 1. HF is an inorganic chemical which dissociates to hydronium and fluoride ions in the environment. As a strong inorganic acid, it has a low potential for adsorption.

Distribution modeling was achieved using EUSES v2.1.1.

References:

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

2. U.S. EPA. 2009. KOCWIN v.2.00