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Environmental fate & pathways

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Perfluoromethyl vinyl ether (PMVE) is a gas at ambient conditions with a boiling point of -26°C (Yaws, Carl L. ©2010 Knovel). PMVE is also characterized by limited water solubility. The value of water solubility of 31.5 mg/l was experimental determined in a completely sealed system with an atmosphere saturated with PMVE. The experimental test conditions did not represent the natural condition in the environment and therefore, although the value of 31.5 mg/l itself reveals a slight water solubility, it represents an overestimation of the actual water solubility of PMVE in the natural system.

On the basis of the above quoted physico-chemical properties, PMVE is expected to distribute into atmosphere.

Even the Henry’s Law constant of 32.100 Pa m3/mol (HENRYWIN v3.20, EPI Suite v4.0), suggests that the substance is expected to rapidly volatilise from water to the air.

 

In order to evaluate the environmental fate of PMVE, a Level III fugacity model was conducted (EQC Fugacity III Model, v.1.0, May 2003), assuming steady-state but not equilibrium conditions.

The Level III fugacity model predicts partitioning between four environmental compartments (air, soil, sediment and water) using a combination of default parameters and various input physico-chemical parameters. The model was run assuming emissions only to air. In fact, in case of an accidental emission, PMVE is uniquely released to air, because of its volatility at ambient conditions and boiling point of -26 °C.

The environmental fate of the substance, assessed through the model, confirmed that, following emissions in air, PMVE remains in this compartment. The rates of transfer to soil and water are very low and only negligible amounts of the total emission remain in these media and in sediment.

 

In the atmosphere the substance is rapidly degraded by reactions with photochemically produced hydroxyl radicals (OH). The products of the atmospheric degradation of PMVE are the same generating from HFCs photooxydation (HF, CF3OCFC(O)F) and do not contribute to ozone depletion.

With respect to reactions with hydroxyl radicals, a degradation rate constant of 2.6 (+/- 0.3) x 10^-12 cm3 molecule^-1s^-1(at 296 K and 700 Torr) and an atmospheric lifetime of 0.023 years (8 days) have been estimated for PMVE

(Mashino, M. et al, 2000). The global warming potential (GWP) for PMVE, estimated using the radiative forcing, lifetime and molecular weight, was considered to be negligible (Zhuangjie L. et al, 2000).

Hydrolysis studies cannot be conducted with volatile substances (section 2 of REACH Annex XI). However, although no partition into water is expected, the tendency to be hydrolyzed has been however assessed basing on the chemical structure of PMVE molecule. This does not contain any functional groups associated with hydrolysis properties at relevant environmental conditions. Particularly, the carbon-fluorine bond is the strongest bond in organic chemistry (O'Hagan, 2008). Substitution of hydrogen atoms with fluorine results in increased bond strengths for both carbon-fluorine and adjacent carbon-carbon bonds over the corresponding hydrocarbon and would increase the resistance to hydrolysis (Lemal, 2003). Therefore, based on this qualitative structure-activity relationship, it can be concluded that hydrolysis is not a relevant degradation mechanism for this substance.

 

 

Although no release to the aquatic environment is expected on the basis of PMVE profile and on its environmental fate, a further assessment based on Quantitative Structure Activity Relationships (QSARs) has been however applied.

 

In particular, the ready biodegradability of PMVE has been estimated with a model prediction BIOWIN v.4.10, EPI Suite v.4.0 which result reports that the substance is not readily biodegradable.

No experimental bioaccumulation data are available for the substance; however, in order to evaluate the bioaccumulation hazard of profile of PMVE, the BCFBAF model v.3.0, EPI Suite v 4.0 has been applied.

The model prediction for PMVE yielded a BCF of 3.993 (log BCF = 0.601), indicating that PMVE has a very low potential to bioaccumulate in aquatic organisms.

 

No releases to the soil are expected on the basis of PMVE profile and environmental fate, however the KOCWIN model v 2.0, EPI Suite v 4.0 has been appliedin order to evaluate the soil adsorption hazard profile of PMVE.

On the basis of the model results, estimated both with the Molecular Connectivity Index (MCI) and with the log Kow (KOCWIN model v 2.0, EPI Suite v 4.0), it is deemed unlikely that PMVE can adsorb to sediment and particulates matter.

 

On the basis of the above reported evaluations, the substance is not expected to persist in the environment. In fact, the whole amount of PMVE released to air partitions in this compartment where it is readily photochemically degraded.