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Long-term toxicity to aquatic invertebrates

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Description of key information

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


- Exposure of aquatic organisms is not significant and exposure-based adaptation is applied according to Annex XI, Section 3


- Short-term toxicity of the test substance and degradation products to aquatic invertebrates is low (> 500 mg/L).


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

Key value for chemical safety assessment

Additional information

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


- Exposure of aquatic organisms is not significant and exposure-based adaptation is applied according to Annex XI, Section 3


- Short-term toxicity of the test substance and degradation products to aquatic invertebrates is low (> 500 mg/L).


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


 


Exposure of aquatic organisms to trimethoxy(propyl)silane (CAS No. 1067-25-0) is absent or not significant and exposure-based adaptation in accordance with Annex XI, Section 3 is applied.


Trimethoxy(propyl)silane hydrolyses rapidly in contact with water (DT50 = 2.6 h, QSAR) to form propylsilanetriol and methanol (CAS No. 67-56-1).


The REACH guidance (ECHA 2010, 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, propylsilanetriol. The other hydrolysis product, methanol, is known for its absence of environmental toxicity at levels up to the highest tested concentrations (OECD SIDS, 2004). Therefore, 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 contributory to the overall aquatic toxicity profile 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 the registered substance itself is available for all three trophic levels (fish, aquatic invertebrates and algae). The available experimental data showed no short-term aquatic hazard to any of the three trophic levels (all acute effect values > 500 mg/L).


For long-term aquatic toxicity, one experimental study is available showing no long-term effects to aquatic algae (effect value > 500 mg/L).


 


Since no hazard was identified in the available aquatic toxicity studies, no PNECs aqua (freshwater/marine water) were derived. However, for the purpose of exposure-based adaptation as in 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) is based on the lowest available short-term effect value for the hydrolysis product propylsilanetriol (LC50 (96 h) > 746 mg/L, equivalent to 554 mg/L when expressed in terms of the propylsilanetriol), which was derived by application of the standard assessment factor of 1000 according to Guidance R.10 (ECHA, 2008).


 


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 aquatic invertebrates 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. 


 


 


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