Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
34 mg/L
Assessment factor:
1 000
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
340 mg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
3.4 mg/L
Assessment factor:
10 000
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:
122 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Sediment (marine water)

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

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

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

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

PNECwater

The registration substance HD5 was not toxic at a loading rate of 100 mg/l in short-term studies with Daphnia and algae. In addition the substance hydrolyses very rapidly in water (half-life for degradation of parent 2.2 minutes at pH 7 and 25°C). Therefore, it is not appropriate to derive PNECs for the parent substance.

Degradation to small molecule silanols is predicted to be rapid, full hydrolysis of the Si-H groups to give the final product methylsilanetriol is expected to be slower but still complete in approximately 1 day. Therefore, it is appropriate to derive PNECs for methylsilanetriol. L(E)C50’s for this substance have been calculated using an appropriate validated QSAR method (PFA 2013an).

The PNECaquatic(freshwater)is therefore based on the lowest LC/EC50value (EC50: 34000 mg/l for algae) that has been determined for methylsilanetriol using the QSAR method.

Short-term data are available for three trophic levels; therefore, an assessment factor of 1000 is applied.

Therefore, PNECaquatic (freshwater)is 34000/1000 = 34 mg/l.

Since no data are available for marine species the PNECaquatic (marine water)is derived from the short-term freshwater species toxicity data with an additional assessment factor of 10.

Therefore, PNECaquatic (marine water)is 34000/10000 = 3.4 mg/l.

Where freshwater releases are intermittent, it is appropriate to reduce the assessment factor to 100.

Therefore, PNECaqua (intermittent releases)is 34000/100 = 340 mg/l.

PNECsediment

There are no measured data for sediment-dwelling organisms.The PNEC values for the sediment compartment have therefore been derived from the PNECs for the aquatic compartment using the equilibrium partitioning approach in conjunction with the predicted log KOCof thehydrolysis product, methylsilanetriol (-2.8) and the Ksusp-watervalue of 0.9 as follows:

PNECsediment

=

Ksusp-water

*  PNECaquatic(freshwater)*  1000

 

 

RHOsusp

 

For methylsilanetriol this is:

PNECsediment

=

0.9

*   34  *  1000

 

 

1150

 

 

 

 

 

 

=

26.6 mg/kg wwt

In the absence of measured data, it is not appropriate to use assessment factors to determine PNECsedimentvalues. The log Kowof the hydrolysis product is <3, therefore, no additional assessment factor is needed to account for possible uptake via sediment ingestion.

Hence a PNECsediment(freshwater)of 26.6 mg/kg wwt, equivalent to 122 mg/kg dwt, will be used for risk characterisation. The same equation is used to derive the PNECsediment(marine water) and substituting the PNECaquatic(freshwater)with the PNECaquatic(marine water)to determine a PNECsediment(marine water)of 2.66 mg/kg wwt and 12.2 mg/kg dwt.

PNECsoil

There are no measured data for soil-dwelling organisms.The PNEC value for the soil compartment has therefore been derived from the PNEC for the aquatic compartment using the equilibrium partitioning approach in conjunction with the predicted log KOCof the hydrolysis product, methylsilanetriol (-2.8) and the Ksoil-watervalue of 0.2 as follows:

PNECsediment

=

Ksoil-water

*  PNECaquatic(freshwater)*  1000

 

 

RHOsoil

 

For methylsilanetriol this is:

PNECsediment

=

0.2

*   34  *  1000

 

 

1700

 

 

 

 

 

 

=

4 mg/kg wwt

 

In the absence of measured data, it is not appropriate to use an assessment factor to determine a PNECsoilvalue. The log Kowof the hydrolysis product is <3, therefore, no additional assessment factor is needed to account for possible uptake via sediment ingestion.

Hence a PNECsoilof 4 mg/kg wwt, equivalent to 4.5 mg/kg dwt, will be used for risk characterisation.

Conclusion on classification

It is proposed that the substance should not be classified for the environment on the basis of EC50s of >100 mg/l for daphnia and algae.