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Environmental fate & pathways

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Releases of perfluoromethylmorpholine (PMM) are anticipated to be solely to the atmospheric compartment. This compound will not partition to terrestrial or aquatic compartments from the atmosphere based on partition coefficients (see below).

The high experimental vapor pressure (217.7 mm Hg) and high experimental Henry’s Law constant (7060 dimensionless or 1.73E+07 Pa∙m³/mol or 171 atm∙m³/mol) indicate that PMM is expected to partition from wet or dry terrestrial surfaces into the atmosphere. PMM has an experimental soil atmosphere partitioning half life of 66.1 ± 16.0 minutes, and indicates that it will be removed soil and sediments quickly. This half life may underestimate the atmospheric partitioning from natural soils due to the layer of water on soils particulates (volatilization driven by water-atmosphere partitioning rather than soil-atmosphere partitioning).

Henry’s Law constant (HLC) is used to describe the tendency for a substance to partition from water to air, the higher the value the greater the tendency for partitioning from water to air. For PMM, an experimentally measured HLC 171 atm∙m³/mol was determined at 22 °C. Based on this HLC value, PMM is likely to volatilize from the aquatic compartment into the atmosphere.

The logarithm of the normalized organic carbon adsorption coefficient (log Koc) is used to describe the tendency for a substance to partition from water to soils or suspended solids. The experimental water solubility of PMM is slight (758 µg/L) and log Koc of PMM was calculated(1) to be 3.6 based on the experimental log Kow (4.3). Based on these data PMM is anticipated to partition from water to soils and suspended solids for a short period of time. Given the rapid partitioning to the atmosphere from soils and from water, the overall net partitioning will be to the atmosphere.

The logarithm of the octanol air partition (log Koa) coefficient is used to describe the tendency of a substance to partition from air into the lipid rich tissues of air breathing organisms. The logarithm of the octanol air partition coefficient (log Koa) of PMM was calculated to be 0.45 based on the experimentally measured dimensionless Henry’s Law constant (7060 dimensionless) at 22 °C and the experimentally determined log Kow of 4.3 (19953 dimensionless) at 23 °C. This log Koa value indicates that PMM has a low potential to partition from air to the lipid rich tissues of air-breathing organisms.

All of the members of this category stem from the same manufacturing process, have similar physicochemical properties including high vapor pressure and low water solubility relative to the hydrocarbon analogs (e. g., hexanes v. perfluorohexanes), and also lack any chemically reactive groups, which forms the technical basis for the category. Members of this category are fully fluorinated, meaning that fluorine, rather than hydrogen, is bonded to all carbon atoms in the molecule. Fluorine is the most electronegative of the elements (fluorine has an electronegativity of 3.98 on the Pauling scale, as compared to 2.55 for carbon or 2.20 for hydrogen). This electronegativity is expected to dominate over all other aspects of substance chemistry and is the underlying basis for similarity of substances in this category. Because these substances exhibit similarity in their physicochemical properties and toxicological properties in mammals, and because available data indicates that parent molecules are not reactive toward biological molecules and cannot undergo bioactivation or indeed any reaction by normal enzymatic processes, they are considered to constitute a chemical category. Data gaps for transport and distribution can therefore be addressed by read-across between category members. Please see IUCLID section 13 for the category justification and a matrix of physicochemical and distribution data for members of the Perfluorinated Organic Chemicals C5-C18 category.

(1) European Chemicals Bureau: Technical Guidance Document of Risk Assessment, Chapter 4.