Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.25 mg/L
Assessment factor:
500
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
2.5 mg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.025 mg/L
Assessment factor:
5 000
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
3.2 mg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
2 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
0.2 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Hazard for air

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
0.25 mg/kg soil dw
Extrapolation method:
equilibrium partitioning method

Hazard for predators

Additional information

For the aquatic compartment, the PNEC is considered entirely by read across from chlorotrimethylsilane and its hydrolysis product trimethylsilanol. An alternative read across approach, from dimethylsilanediol is considered to be slightly less relevant but would not affect the conclusions. No other data are included in the discussion, although a Category approach is used to discussion of the assessment factors.

The standard approach to PNEC calculation when acute data are available for three trophic levels is to apply an assessment factor of 1000 to the lowest lethal or effect concentration (E(L)C50). However, this assessment factor may be reduced by up to a factor of 10 if this is justified by the available data, for example:

  • Evidence from structurally similar compounds which may demonstrate that a higher or lower factor may be appropriate.
  • Knowledge of the mode of action as some substances by virtue of their structure may be known to act in a non-specific manner. A lower factor may therefore be considered. Equally a known specific mode of action may lead to a higher factor (ECHA 2009).
Trimethylsilanol is part of a category of organosilicon substances containing only alkyl, halogen, alkoxy or silanol groups attached to the Si atom. The category has a low hazard profile and data are consistent with a simple polar narcosis mechanism. It is considered that the weight of evidence for the number of substances (ca.40 substances have reliable measured data) justifies a reduction of the assessment factor from the normal value of 1000. A value of 500 is used, to reflect the increased confidence in the individual values due to the low variability across the category. This is discussed further in PFA, 2010.

Conclusion on classification

It is proposed that chlorodimethylsilane should not be classified in the EU for acute or chronic toxicity on the grounds that reliable studies for the silanol hydrolysis product indicate that it would not be toxic at a loading rate of 100 mg/l. The substance hydrolyses rapidly and the silanol hydrolysis product has a low log Kow.