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Environmental fate & pathways

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The distribution of F-D3in a sewage treatment plant (STP) has been estimated using the SimpleTreat model (implemented in EUSES 2.1.2).

It is in accordance with the SimpleTreat model to ensure that the solubility limit of the substance in treated effluent (including the fraction adsorbed to suspended matter in the effluent) is not exceeded. The fraction directed to water in the STP may need to be manually reduced such that the appropriate threshold concentration limit is not exceeded in the resulting value of concentration of chemical in local effluent. This adjustment of the fraction directed to water in the STP was necessary in this case, and the mass balance of 100% was reasserted by manually increasing the fraction directed to other pathways in the STP (specifically, to sludge).

The resulting estimated distribution of F-D3 in a sewage treatment plant is shown in the table below.

Table Distribution modelling for STP

 

2,4,6-Trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane

 

Fraction of emission directed to air by STP

≤6.8

[%]

Fraction of emission directed to water by STP

≤0.1

[%]

Fraction of emission directed to sludge by STP

≥93.2

[%]

Fraction of the emission degraded in STP

0

[%]

 

Note: the fraction modelled by SimpleTreat to be volatilised is very likely to be over-estimated. The properties of F-D3 suggest that only fully-dissolved F-D3 would tend to volatilise. In reality, given the typical workings of a sewage treatment plant it is far more likely that any F-D3 in a mixed wastewater will be associated with solids and suspended matter, and, based on its Kocand Kdvalues, F-D3 is likely to remain adsorbed until the solids are separated as sludge, thus only a negligible fraction would be truly dissolved and available for volatilisation. Therefore, the estimated fractions to sludge and to air are considered to be minimum and maximum limit values respectively; the fraction to sludge may be much nearer to 100%.