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The distribution in a sewage treatment plant (STP) has been estimated using the SimpleTreat model (implemented in EUSES 2.1.2/Chesar 3.4), see table below.

The distribution calculation is done for the silanol hydrolysis products due to the expected rapid hydrolysis of the constituents of the submission substance.

Table: Distribution modelling for STP

 

Methylsilanetriol (Silanol HP-X)

5-Oxa-9-aza-1,13-disilatridecane-1,1,1,7,13,13,13-heptol (Silanol HP-Y)

(3-Aminopropyl)silanetriol (Silanol HP-Z)

  

Fraction of emission directed to water by STP

 99.99

 99.99

 99.99

[%]

Fraction of emission directed to air by STP

 2.57E-7

 0

4.66E-11

[%]

Fraction of emission directed to sludge by STP

 7.51E-3

 3.13E-3

3.13E-3

[%]

Fraction of the emission degraded in STP

 0

 0

 0

[%]

The constituents of the submission substance are expected to hydrolyse rapidly with hydrolysis half-lives of <12 hours at pH 7 and 20-25°C to the corresponding silanol hydrolysis products and ethanol and/or methanol.

Ethanol and methanol are readily biodegradable (OECD 2004a and OECD 2004b).

On the basis of available data, the silanol hydrolysis products have low vapour pressure and/or low Henry's Law Constant, low adsorption potential (low log Kow/log Koc), high water solubility and are not expected to biodegrade.

Therefore water is the main compartment to which the hydrolysis products are expected to partition in a sewage treatment plant.