Triethoxy(phenyl)silane

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

fish early-life stage toxicity

Data waiving:

exposure considerations

Justification for data waiving:

other:

Description of key information

A long-term toxicity study on fish is not necessary as:

- exposure considerations in accordance with Annex XI, Section 3, indicate that exposure of aquatic organisms to triethoxy(phenyl)silane (CAS No. 780-69-8) is absent or not significant

and

- the substance has a moderate hazard potential based on the available toxicity data.

Additional information

In accordance with Annex XI, Section 3, exposure of aquatic organisms to triethoxy(phenyl)silane (CAS 780-69-8), is absent or not significant.

The environmental hazard assessment, PNEC derivation and risk characterization is based on the silanol hydrolysis product, phenylsilanetriol, as the substance hydrolyses rapidly (DT50 = 1.5 h at 20-25 °C and pH 7, QSAR). The other hydrolysis product, ethanol, is known for its absence of environmental toxicity (OECD SIDS, 2004) and thus can be disregarded in the environmental hazard assessment.

Aquatic toxicity data on the parent compound is only available for aquatic invertebrates, for the other two trophic level (fish and algae) good quality data was read-across from a structural analogue substance trichlorophenylsilane (CAS 98-13-5). The source substance hydrolyses rapidly under environmental conditions (DT50 < 1 min at 25°C and pH 4, 7 and 9) to form the structural similar hydrolysis product phenylsilanetriol and hydrogen chloride. The second hydrolysis product, hydrogen chloride, readily dissociates in water into hydrated protons and chloride anions. Thus, it is ionised and neutralisation depends on the buffer capacity of the receiving water. Toxicity only occurs when the buffering capacity of the receiving water is exceeded and pH values fall below pH 6. The pH in rivers and lakes fluctuates within a natural range. The natural pH range in aquatic systems is generally not expected to be perturbed to a relevant extent by anthropogenic emissions when appropriate risk control measures are in place. Variations in effect values of experimental studies can largely be explained by variations in the buffer capacity of the test media (OECD SIDS, 2002). Thus, hydrochloric acid is not expected to have a significant impact on the overall aquatic toxicity of the source compound.

The hazard assessment showed only moderate short-term effects in aquatic invertebrates (daphnia) with an EC50 (48h) = 37 mg/L. No acute effects were observed in fish an algae (EC/LC50 values > 100 mg/L). Consequently, the 48-h EC50 of 37 mg/L obtained in the study on aquatic invertebrates was used for the PNEC derivation as outlined in chapter 6. The silanol hydrolysis product of the registered compound is very well water-soluble. Significant deviations from this overall ecotoxicity profile are not expected and greater long-term toxicity in fish is considered unlikely.

The risk characterization for the silanol hydrolysis product indicated no risk to the aquatic environment (RCR < 1). For detailed information on the risk assessment please refer to the attached documentation in Section 13.

 

References:

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

OECD, 2002. Hydrogen Chloride - SIDS Initial Assessment Report for SIAM 15, Boston, USA: UNEP Publications.