Dimethoxymethylsilane

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

fish life cycle toxicity

Data waiving:

other justification

Justification for data waiving:

other:

Description of key information

Testing for long-term toxicity to fish is not considered necessary because:

- Exposure of aquatic organisms is not significant, according to Annex XI, Section 3

- Short-term toxicity of the test substance and degradation products to fish is low (> 100 mg/L).

- The risk characterisation ratio (RCR) based on PNECaquatic (freshwater) is <<1.

Additional information

Testing for long-term toxicity to fish is not considered necessary because:

- Exposure of aquatic organisms is not significant, according to Annex XI, Section 3

- Short-term toxicity of the test substance and degradation products to fish is low (> 100 mg/L).

- The risk characterisation ratio (RCR) based on PNECaquatic (freshwater) is <<1.

Exposure of aquatic organisms to dimethoxy(methyl)silane (CAS No. 16881-77-9) is absent or not significant and therefore exposure-based adaptation in accordance with Annex XI, Section 3 is applied.

Dimethoxy(methyl)silane undergoes a rapid two-step hydrolysis under environmental conditions through which methylsilanediol (first step) and methylsilanetriol (second step) is formed. The non-silanol hydrolysis product that is formed is methanol.

REACH guidance (ECHA 2010A, 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”. TGD and ECHA guidance (EC 2003, ECHA 2010A) also suggest that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Therefore, the environmental hazard assessment, PNEC derivation and risk characterization is based on the silanol hydrolysis product, which is anticipated to be the second hydrolysis product methylsilanetriol. The other hydrolysis product, methanol, is known for its absence of environmental toxicity at levels up to the highest tested concentrations (OECD SIDS, 2004). The alcohol hydrolysis product, methanol is not considered to be hazardous to aquatic organisms (see Section 6.1). The effect concentrations derived for methanol in standard guideline studies are all well above 100 mg/L (OECD SIDS, 2004). Thus, methanol is not considered to contribute to the overall aquatic toxicity of the target substance and thus not relevant for the assessment of aquatic toxicity.

 

For the short-term aquatic toxicity of the registered substance, data for all three trophic levels (fish, aquatic invertebrates and algae) are available by means of read-across. An OECD 202 for the substance itself is currently ongoing and the dossier will be updated, once the final results have been received. The available experimental short-term toxicity data showed no toxicity up to the highest concentration tested (IUCLID Section 6.1, Table 1).

For long-term aquatic toxicity one experimental study is available for the toxicity toward aquatic invertebrates (IUCLID Section 6.1, Table 1) showing no adverse effects up to the highest concentration tested.

 

Since no hazard was identified in the available short-term and long-term aquatic toxicity studies, no PNECs aqua (freshwater/marine water) were derived. However, for the purpose of exposure-based adaptation applied to the present endpoint, PNECs were derived in the Chemical Safety Report (CSR, Chapters 9 and 10) for the required risk characterization even though no hazard was identified in the available aquatic toxicity studies.

The PNEC aqua (freshwater/marine water) for the hydrolysis product methylsilanetriol was derived by application of an assessment factor of 50 (freshwater) and 500 (marine water) to the lowest long-term effect value from two long-term results available for two trophic levels (NOEC (21 d) of ≥ 10 mg/L for aquatic invertebrates), in accordance with Guidance R.10 (ECHA, 2008).

An assessment factor of 50 applies when two long-term results are available covering the most sensitive species from the short-term tests. No effects were reported in the short- term tests. Therefore, it was not possible to assess the sensitivities of the test species. However, it was not considered appropriate to increase the assessment factor to 100 due to the high water solubility of the substance and the fact that the concentrations tested during the short-term tests were very high and no effects were observed.

The derived PNECs are indicative only and no hazard is expected. This indicative aquatic PNEC for methylsilanetriol was used to derive the PNECs for sediment and soil using the equilibrium partitioning method. 

 

The registered compound and its silanol hydrolysis product are well soluble. Significant deviations from this overall ecotoxicity profile are not expected and greater long-term toxicity in an additional test with fish is considered unlikely. The risk characterization for the silanol hydrolysis product of the registered compound indicated no risk to the aquatic environment (RCR < 0.01). For detailed information on the risk assessment please refer to the attached documentation in Section 13. 

 

Based on the above described evidence and due to animal welfare reasons, further vertebrate tests can be avoided and no long-term test with fish is considered necessary.

 

 

References:

OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.

 

Guidance on information requirements and chemical safety assessment Chapter R.10: Characterisation of dose [concentration]-response for environment, European Chemicals Agency 2008