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EC number: -
CAS number: 37486-69-4
The BCF base-line model v.02.09 within Catalogic v5.11.17 was used to
model BCF for this substance. The model calculates a maximum BCF based
on log Kow and applies correction factors for metabolism, molecular
size, water solubility, and two other factors not relevant to this
structure. The estimated log Kow used to calculate baseline BCF diverges
from the log Kow value derived from an experimental water
solubility:octanol solubility ratio, and therefore the predicted BCF is
not reported. However, the model reports an average calculated Dmax
across multiple conformers of 18.4 Å, and further supports lack of
metabolic impact on potential bioaccumulation of the substance. Given
this, the model is considered reliable with restrictions and can be used
to support other arguments regarding bioaccumulation.
The gas-phase reorganization energies are within the range of bond
rotation of a methyl group eclipsing another methyl group. However,
conformational reorganization of dissolved substances involves the
reorganization of the solvation sphere surrounding the molecule in
addition to the conformational change of the molecule itself. In
thermodynamic terms, the energy required to reorganize a structure is
the sum of the gas phase reorganization energy plus the energy required
to reorganize the water solvation sphere. Bending the molecule moves
three to four waters per carbon, with an energy requirement far higher
than the rotational energies presented above (1). For this reason,
alkanes up to 16 carbons in length remain linear in water (2). Structure
1, with a Dmax of 2.19 nm, is the most favorable.
1. Mountain, R.D.; Thirumalai, D. Hydration Sphere for a Series of
Hydrocarbons, Proc. Natl. Acad. Sci., 95, 1998, 8436
2. Ferguson, A.L.; Debeneditti, P.G.; Panaglotopoulos, A.Z. Solubilty
and Molecular conformations of n-Alkane Chains in Water, J. Phys. Chem.
B, 113, 2009, 6405
Molecular conformation and energy levels for TFEE-5 were calculated
using SPARTAN v2.0, an ab initio quantum chemical calculation
program. After generation and optimization of structures, the most
energetically favorable is the linear structure having a Dmax of 2.19
nm. Other conformations have a Dmax ranging from 1.74 down to 1.41 nm,
in decreasing order of favorability. Conformational shifts away from
linearity in solution are expected to be inhibited by the energy
requirements of solvent sphere rearrangement. The software is a
commonly-accepted tool used in quantum chemical research, with basis set
universally defined for all atoms. The resulting variable, Dmax and
conformation energy, speak to the ability or lack thereof for a molecule
in a certain conformation to pass a membrane, and to remain in that
conformation. The results are therefore deemed reliable with restriction
and suitable for use in a weight of evidence argument on bioaccumulation.
TFEE-5 is not expected to bioaccumulate.
TFEE-5 is a large and almost completely perfluorinated polyether. TFEE-5
is not ionic, it is not a surfactant, and, therefore, studies and
properties of perfluochemical acids and sulfonates should not be equated
to TFEE-5. Rather, TFEE-5 must be evaluated using the best available
data on this extremely hydrophobic chemistry.
The adsorption and excretion of TFEE-5 was investigated (see section
Toxicokinetics, metabolism, and distribution: basic toxicokinetics) in a
single dose study (907 mg/kg, oral gavage) in male Sprague Dawley rats,
where it was determined that all of the administered dose was recovered
in the feces. The complete recovery indicates that TFEE-5 was not taken
up from the digestive tract. It is widely understood that if a substance
is not taken up by mammals, then it is also likely that the substance
will not easily pass across fish gill membranes and therefore may not
have a high bioconcentration factor (BCF) in fish (1). Support for this
conclusion, the total lack of transport from the digestive tract, is
provided by examinations of molecular size using both SPARTAN molecular
modeling (an ab initio quantum mechanical calculation) and OASIS
Catalogic (CATABOL), which demonstrate that TFEE-5 is too large to cross
biological membranes. Spartan calculated that the lowest energy
conformer had a Dmax of 2.18 nm followed by a molecule with a Dmax 1.74
nm. Three additional and energetically unfavorable conformers were found
with Dmax values ranging from 1.40-1.52 nm. Estimations of the molecular
size using the ECHA recommended Catalogic software showed an average
Dmax of 1.81 nm (range, 1.43 - 2.41 nm). The two calculated values are
in substantive agreement despite using different calculation
methodologies. Using the guidance value of 1.7 nm as the limit for
transport through membranes (1), we conclude that TFEE-5 exists in
stable conformation(s) that are too large to pass through biological
membranes and will therefore not bioconcentrate. BCF modeling using
Catalogic showed little potential for TFEE-5 to bioconcentrate. However,
that estimate utilized an EPISuite calculation for the log Kow which is
higher than the key study log Kow value estimated using the solubilities
of TFEE-5 in water-saturated octanol and octanol-saturated water (see
section Physical and chemical properties: partition coefficient). The
bioconcentration data from Catalogic should be treated as indicative
rather than definitive. We therefore conclude TFEE-5 is not
bioconcentrating in fish.
1) ECHA. 2014. Guidance on Information Requirements and Chemical Safety
Assessment Chapter R.11: PBT/vPvB assessment Version 2.0
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