Registration Dossier

Ecotoxicological information

Ecotoxicological Summary

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Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.25 mg/L
Assessment factor:
100
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:
500
Extrapolation method:
assessment factor

STP

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

Sediment (freshwater)

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

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
0.19 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:
0.2 mg/kg soil dw
Extrapolation method:
equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

The hydrolysis half-life of trimethoxy(octyl)silane (CAS 3069-40-7) is predicted to be 4 hours at 20-25⁰C and pH 7; the substance will therefore undergo rapid hydrolysis in contact with water and atmospheric moisture to form octylsilanetriol and methanol. REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT50 is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. ECHA Guidance Chapter R.7b states that where degradation rates fall between >1 hour and <72 hours, testing of parent and/or degradation product(s) should be considered on a case-by-case basis.

The substance will be exposed to the environment through wastewater treatment plant (WWTP) effluent only. The residency time in the waste water treatment plant is approximately 15 hours with an average temperature of 15°C (assumed to be at neutral pH). Significant degradation by hydrolysis would be expected before the substance is released to the receiving waters. The environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is therefore based on the properties of the silanol hydrolysis product, in accordance with REACH guidance. As described in Sections 4.8 and 5.1.2 of this data set, the silanol hydrolysis products may be susceptible to condensation reactions.

 

The silanol hydrolysis product, octylsilanetriol, is a weak, nonionic surface active substance (see Chapter 4 for further details). The mechanism of toxicity of nonionic surfactants is considered to be the same as nonsurfactant unreactive organic substances, i.e. non polar narcosis. In addition, due to the silanol hydrolysis product only being a weak surfactant, micelles are thought to be produced only at high concentrations, which are not environmentally realistic. The possibility of synergistic effects of micelles and other toxic compounds in the environment is therefore not considered further.

 

Octylsilanetriol has a predicted water solubility of 59000 mg/l and predicted log Kow of 1.1.

 

READ-ACROSS JUSTIFICATION

No measured data are available for the registration substance, or its silanol hydrolysis product. Data have therefore been read across from relevant substances to assess the toxicity of the silanol hydrolysis product to aquatic organisms.

 

Please see the attached report in Section 13 for the analogue approach to address ecotoxicity of trimethoxy(octyl)silane [EC No.: 221-338-7, CAS 3069-40-7].

Conclusion on classification

The substance has reliable short-term E(L)C50 values of >100 mg/L in fish and >100 mg/L in algae. It has a reliable NOEC of ≥100 mg/L in algae and reliable long-term NOEC of 32 mg/L in Daphnia.

 

The substance hydrolyses rapidly in water. The silanol hydrolysis product, octylsilanetriol, is not readily biodegradable but has a log Kow <3.

 

These data are consistent with the following classification under Regulation (EC) No 1272/2008 (as amended) (CLP):

Acute toxicity: Not classified.

Chronic toxicity: Not classified.