Tetraethyl orthosilicate

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

Please see the cross-referenced supporting information to justify the waiving of chronic aquatic toxicity data.
Further discussion on the ecotoxicity of silicic acid producers can be found in the attached report “PFA, 2013x Analogue report Ecotoxicity of (poly)silicic acid producers_20130516”.

Reason / purpose for cross-reference:

data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

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data waiving: supporting information

Conclusions:

Testing for long-term toxicity to invertebrates is not considered necessary because:
- Short-term toxicity to invertebrates is low.
- The risk characterisation ratios (RCR) based on PNECaquatic derived from existing data are <1.

Additional information

On contact with water, tetraethyl orthosilicate (TEOS, CAS 78-10-4; EC No. 201-083-8) rapidly hydrolyses (half-life approximately 4.4 hours at 25°C and pH 7) to monosilicic acid (CAS 10193-36-9; EC No. 233-477-0) and ethanol (CAS 64-17-5; EC No. 200-578-6). Due to the rapid hydrolysis of the substance, the chemical safety assessment (CSA) is based on the silicon containing hydrolysis product monosilicic acid. The consideration of ethanol is discussed in IUCLID Section 6, CSR Section 7.0.

No long-term toxicity to aquatic invertebrates data are available with the registered substance or with monosilicic acid, on which the CSA is based. Testing for long-term toxicity to aquatic invertebrates is not considered necessary because:

Based on the short-term aquatic data set in which the organisms were exposed to the hydrolysis products, no effects were seen in any trophic level at the highest concentrations tested (the studies were carried out at or above loadings of 100 mg/l parent substance). As no effects were observed, there is no indication of higher sensitivity in invertebrates compared to fish and algae.

The rapidly generated hydrolysis product, monosilicic acid, is inorganic, water-soluble and has low potential for bioaccumulation (refer to IUCLID Section 5.3 for further information).

Due to monosilicic acid being inorganic, PBT assessment does not apply and the substance cannot be classed as PBT or vPvB.

On the basis of structure, monosilicic acid has a high affinity for water and low affinity for lipids and organic carbon. In addition, silicic acid and its condensation products are unlikely to diffuse across membranes or accumulate in fatty tissues, and are expected to be effectively eliminated in faeces and via the kidneys in urine (refer to IUCLID Section 7.1 for further information). There is therefore no evidence to suggest that this substance will accumulate in the body.

The substances in the silicic acid producers analogue group are silicon compounds with no carbon attached that contain no structural features indicative of a specific mode of toxic action for ecotoxicity.

Monosilicic acid exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100-150 mg/l as SiO₂ to give a dynamic equilibrium between monomer, oligomers and insoluble polysilicic acid. (Poly)silicic acid is a naturally occurring substance, ubiquitous to the natural environment, which is not harmful to aquatic organisms at relevant environmental concentrations. Monosilicic acid is the major bioavailable form of silicon for aquatic organisms and plays an important role in the biogeochemical cycle of silicon (Si). Most living organisms contain at least trace quantities of silicon. For some species Si is an essential element that is actively taken up. For example, diatoms, radiolarians, flagellates, sponges and gastropods all have silicate skeletal structures (OECD SIDS 2004, Synthetic amorphous silica and silicates; PFA, 2013x). (Poly)silicic acid has been shown to be beneficial in protection against mildew formation in wheat and to be non-phytotoxic in non-standard studies (Côte-Beaulieu et al. 2009).

Further discussion on the ecotoxicity of silicic acid producers can be found in the attached report “PFA, 2013x Analogue report Ecotoxicity of (poly)silicic acid producers_20130516”.

As inorganic substances, soluble silicates are not amenable to photo- or biodegradation (OECD SIDS 2004, Synthetic amorphous silica and silicates), therefore will not give rise to toxic degradation products.

The bioavailable form of silica is dissolved silica [Si(OH)₄], and almost all of it is of natural origin (OECD SIDS 2004, Synthetic amorphous silica and silicates). Anthropogenic sources of silicic acid will rapidly depolymerise in the aquatic environment to give molecular species indistinguishable from natural dissolved silica (OECD SIDS 2004, soluble silicates). The potential releases of inorganic silicon resulting from use of the registered substance are negligible compared to the natural flux of silica in the environment (refer to IUCLID Section 5 endpoint summary for further information).

Because silicic acid occurs naturally in the environment and organisms are naturally adapted to utilise silica, and because monosilicic acid, oligomeric and polysilicic acids from anthropogenic sources will enter the natural biogeochemical cycles and will be indistinguishable from naturally occurring silica, the registered substance, which rapidly hydrolyses to silicic acid, is not expected to be harmful to organisms present in the environment.

There are no chronic aquatic toxicity data for silicic acid, but due to the known inherent physico-chemical properties, absence of acute toxic effects as well as the ubiquitous presence of silicic acid in the environment, there is no evidence of harmful long-term effects arising from exposure to silicic acid and its condensation products.

Overall, it is concluded that no hazard is identified and therefore further testing is not considered necessary.  

Details on how the substance is evaluated for risk can be found in IUCLID Section 6.0, and Chapters 7, 9 and 10 of the Chemical Safety Report.

References

Côte-Beaulieu, C. Chain, F. Menzies, J.G. Kinrade, S.D. Belanger, R.R. (2009) Absorption of aqueous inorganic and organic silicon compounds by wheat and their effect on growth and powdery mildew control. Environmental and experimental botany, 65: 155-161.

OECD SIDS 2004, soluble silicates. SIDS Initial Assessment Report for SIAM 18, Paris, France, 20-23 April, 2004, Soluble Silicates, CAS 1344-09-8 Silicic acid, sodium salt; CAS 6834-92-0.

OECD SIDS 2004, Synthetic amorphous silica and silicates. SIDS Initial Assessment Report for SIAM 19. Berlin, Germany, 19-22 October 2004.

PFA 2013x: Peter Fisk Associates, Analogue grouping report: Ecotoxicity of (poly)silicic acid generating compounds. PFA.300.003.001.