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Perfluoromethylmorpholine (PMM) is of low water solubility (758 µg/L at 23 °C) and is volatile (vapor pressure, 217.7 mm Hg at 20 °C).  An experimental Henry's Law constant (expressed as the ratio of vapor phase partial pressure of PMM over aqueous phase concentration) of 1.73E+07 Pa∙m³/mol (171 atm∙m³/mol) was measured at 22 °C.  Based on its uses, PMM will not be released to aquatic systems or soils.  Upon direct release of PMM to the aquatic compartment, the chemical would be expected to volatilize rapidly.  PMM is not expected to partition from the atmosphere to moist soils or surface waters.  Therefore, no exposure to aquatic organisms is expected.

 

We have proposed adaptation of the data requirement for bioconcentration factor of PMM.  Based on a log Kowof 4.3, the chemical would not be considered bioaccumulative in aquatic organisms.  Also, bioaccumulation of PMM in aquatic organisms would not be expected due to lack of exposure in aquatic systems.  PMM is expected to reside entirely in the atmospheric compartment, so air breathing organisms were evaluated for bioaccumulation potential.  According to Chapter R.7.10.3.4 of the Technical Guidance (Other indication of bioaccumulation potential):

 

For air-breathing organisms, respiratory elimination occurs via lipid-air exchange, and such exchange declines as the octanol-air partition coefficient (KOA) increases, with biomagnification predicted to occur in many mammals at a log KOA above 5. Such biomagnification does not occur if the substance and its metabolites are rapidly eliminated in urine (i.e. have a log KOW of around 2 or less). Thus the bioaccumulation potential in air-breathing organisms is a function of both log KOW and log KOA. In contrast, respiratory elimination in non-mammalian aquatic organisms occurs via gill ventilation to water, and this process is known to be inversely related to the log KOW (hence an increase in log KOW results in a decrease in the rate of elimination and hence increase in the accumulation potential).

 

A log octanol-air partition coefficient (log KOA) of 0.45 at ca. 23 °C was calculated for PMM using the relationship:

 

 

KOA(unitless) = KOW/ KAW

 

 

Where KOW is the octanol:water partition coefficient and KAW is the dimensionless Henry’s Law constant.  As per Kelly and Gobas(1), chemicals with log KOA< 4 do not biomagnify regardless of the KOW because of efficient elimination via air exhalation (or, in this case, extremely inefficient absorption via air inhalation).  According to the classification scheme proposed in Chapter R7.10.3.4, PMM is a non-polar volatile (high log KOW and low log KOA), and is not expected to bioaccumulate in air-breathing organism.  As stated, the potential to accumulate in aquatic organisms is mitigated by the lack of relevance of the aquatic exposure pathway. Therefore, bioaccumulation of PMM in terrestrial or aquatic organisms is not expected.

 

Reference:

 

1) Kelly, B.C. and F.A.P.C. Gobas.  2003.  An Arctic Terrestrial Food-Chain Bioaccumulation Model for Persistent Organic Pollutants.  Environ. Sci. Technol Vol. 37, No. 13, pp 2966–2974.