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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), see table below.

Table: Distribution modelling for STP

Fraction of emission directed to air by STP



Fraction of emission directed to water by STP



Fraction of emission directed to sludge by STP



Fraction of the emission degraded in STP



Hexamethyldisiloxane is not expected to undergo any significant biodegradation, has very high Henry’s Law constant and high log Kow/log Koc. Therefore air is the main compartment to which it is expected to partition in a sewage treatment plant. Some partition to sewage sludge and water is expected, and therefore potentially to soil/sediment compartments in the environment.