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Diss Factsheets
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EC number: 201-083-8 | CAS number: 78-10-4
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
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Toxicity to birds
Administrative data
- Endpoint:
- long-term toxicity to birds
- 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 terrestrial 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”.
Cross-referenceopen allclose all
- Reason / purpose for cross-reference:
- data waiving: supporting information
Reference
There are no in vivo data on the toxicokinetics of tetraethyl orthosilicate (CAS 78-10-4, EC No. 201 -083-8).
The following summary has therefore been prepared based on validated predictions of the physicochemical properties of the substance itself and its hydrolysis products and using these data in algorithms that are the basis of many computer-based physiologically based pharmacokinetic or toxicokinetic (PBTK) prediction models. Although these algorithms provide a numerical value, for the purposes of this summary, only qualitative statements or predictions are made.
The main input variable for the majority of these algorithms is log Kow. So, by using this parameter and, where appropriate, other known or predicted physicochemical properties of tetraethyl orthosilicate or its hydrolysis products, reasonable predictions or statements may be made about their potential absorption, distribution, metabolism and excretion (ADME) properties.
In contact with water, tetraethyl orthosilicate hydrolyses very rapidly, with a hydrolysis half-life of 0.11 hr (6.6 min), 4.4 hr and 0.22 hr (13 min) at pH 4, 7 and 9 respectively and at 25°C, to form monosilicic acid. 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. The timing and rate of condensation is regulated by the concentration, pH, ionic strength, temperature etc. The non-silanol product of hydrolysis is ethanol. The toxicokinetics of ethanol have been extensively studied previously and therefore are not discussed further in this summary.
Human exposure to tetraethyl orthosilicate can occur via the inhalation or dermal routes.
Some toxicokinetic work may help identify or predict the predominant chemical entity (monosilicic versus polysilicic acid) present in the small intestine, the primary site of gastrointestinal absorption or in the nasal mucosa, the site of respiratory inflammation in the reliable repeat inhalation studies (Omae et al. 1995, Nakashima et al. 2014).
Absorption
Oral
Significant oral exposure is not expected for tetraethyl orthosilicate.
When oral exposure takes place, it can be assumed, except for the most extreme of insoluble substances, that uptake through intestinal walls into the blood occurs. Uptake from intestines can be assumed possible for all substances that have appreciable solubility in water or lipid. Other mechanisms by which substances can be absorbed in the gastrointestinal tract include the passage of small water-soluble molecules (molecular weight up to around 200 g/mol) through aqueous pores or carriage of such molecules across membranes with the bulk passage of water (Renwick, 1993).
If oral exposure of tetraethyl orthosilicate occurs, its molecular weight (208 g/mol) and water solubility (8600 mg/L) favour absorption following oral (neat or aqueous) ingestion. However, tetraethyl orthosilicate will rapidly hydrolyse (hydrolysis half-life at pH 4 is 6.6 minutes; and approximately 5 seconds at pH 2) to monosilicic acid in the stomach, thus making the absorption of tetraethyl orthosilicate following ingestion unlikely. The hydrolysis product monosilicic acid would be absorbed from the gastrointestinal tract (primarily small intestine); whereas absorption of the condensed insoluble polysilicic acid will be insignificant when compared to the absorption of the soluble species (Carlisle, 1986).
In the repeated dose oral study with the tetraethyl orthosilicate condensed hydrolysis product polysilicic acid (equivalent to synthetic amorphous silica [SAS], Kim et al. 2014), there were no significant adverse effects identified (author conclusion of a systemic NOAEL at the highest dose tested). Although systemic (renal) findings were observed in the repeated dose oral study with tetraethyl orthosilicate (CIT Safety & Health Laboratories 2005), this result is considered a consequence of the corn oil dosing (see repeated dose endpoint summary).
Dermal
The fat solubility and therefore potential dermal penetration of a substance can be estimated by using the water solubility and log Kow values. Substances with log Kow values between 1 and 4 favour dermal absorption (values between 2 and 3 are optimal) particularly if water solubility is high.
With a water solubility of 8600 mg/L and log Kow of 1.4, tetraethyl orthosilicate is in the favourable range for dermal absorption, and therefore could be absorbed prior to hydrolysis in the absence of moisture on the skin. After or during deposition of a liquid on the skin, evaporation of the substance and dermal absorption occur simultaneously such that the vapour pressure of a substance is also relevant. With a vapour pressure of 20 Pa at 20°C, evaporation of tetraethyl orthosilicate is not likely to be a major factor influencing potential dermal absorption.
Although the molecular weight of the hydrolysis product monosilicic acid favours absorption across the skin, it is water soluble (approximately 100 - 150 mg/L as ‘SiO2 equivalent’ with condensation to insoluble polysilicic acid occurring at higher concentrations). This solubility suggests that monosilicic acid is too hydrophilic to cross the lipid rich stratum corneum. Thus, absorption of the soluble monosilicic acid and the condensed insoluble polysilicic acid across the skin is unlikely.
Inhalation
There is a Quantitative Structure-Property Relationship (QSPR) to estimate the blood: air partition coefficient for human subjects as published by Meulenberg and Vijverberg (2000). The resulting algorithm uses the dimensionless Henry coefficient and the octanol: air partition coefficient (Koct: air) as independent variables.
Using these values for tetraethyl orthosilicate results in a blood: air partition coefficient of approximately 910: 1 meaning that if respiratory exposure occurred there could be uptake of tetraethyl orthosilicate into the systemic circulation. However, given the rapid hydrolysis of tetraethyl orthosilicate, it is expected that the entity absorbed across the respiratory (nasal) mucosa would be the monosilicic acid hydrolysis product.
Although systemic (renal) effects were identified in reliable repeated-dose inhalation toxicity studies with tetraethyl orthosilicate (Omae et al., 1995, Nakashima et al. 1994), these findings are considered consistent with a physical effect of insoluble polysilicic acid formation within the kidneys, rather than tetraethyl orthosilicate toxicity (see repeated dose endpoint summary).
Distribution
As discussed above, the predicted absorbed entity is the monosilicic acid hydrolysis product, rather than tetraethyl orthosilicate or polysilicic acid. Monosilicic acid, is a small polar molecule, and therefore has potential to be widely distributed, but its hydrophilic nature will limit its diffusion across membranes (including the blood-brain and blood-testes barriers) and its accumulation in fatty tissues. Human blood contains 1 mg SiO2/L of monosilicic acid (Iler RK, 1979).
For blood: tissue partitioning of the parent substance, a QSPR algorithm has been developed by De Jongh et al. (1997) in which the distribution of compounds between blood and human body tissues as a function of water and lipid content of tissues and the n-octanol: water partition coefficient (Kow) is described.
Tetraethyl orthosilicate quickly hydrolyses to monosilicic acid thus limiting its systemic absorption and therefore distribution. So, the following predicted distribution of tetraethyl orthosilicate to the fatty tissues is not considered likely.
Table 5.1.1 Tissue: blood partition coefficients
|
Log Kow |
Kow |
Liver |
Muscle |
Fat |
Brain |
Kidney |
Tetraethyl orthosilicate |
1.4 |
25.12 |
1.3 |
1.1 |
18.4 |
1.3 |
1.1 |
Metabolism
Besides the aforementioned hydrolysis, there is no information on the potential metabolism of tetraethyl orthosilicate.
Silicon is an essential trace element participating in the normal metabolism of higher animals. It is required in bone, cartilage and connective tissue formation as well as participating in other important metabolic processes. The silicon is present almost entirely as free, soluble monosilicic acid (Carlisle 1986).
The available and negative genetic toxicity tests in vitro showed no observable differences in effects with and without metabolic activation.
Excretion
As discussed in the repeated dose endpoint summary, all of the tetraethyl orthosilicate would be expected to hydrolyse to monosilicic acid in the gastrointestinal tract after oral exposure or in the nasal mucosa following inhalation. Any absorbed soluble monosilicic acid would either condense to polysilicic acid in the kidneys or be excreted via urine as monosilicic acid. Condensed and insoluble polysilicic acid formed in the gastrointestinal or nasal mucosa would not be absorbed systemically, and thus only excreted in faeces.
- Reason / purpose for cross-reference:
- data waiving: supporting information
Reference
Bioaccumulation: aquatic/sediment: Low potential for bioaccumulation
Testing is waived in accordance with Column 2 of REACH Annex IX. Direct or indirect exposure of aquatic organisms to the registered substance is very limited due to the instability of the substance in water. The substance hydrolyses rapidly in contact with water to form monosilicic acid [CAS 10193-36-9; EC No. 233-477-0, Si(OH)4] and ethanol (CAS 64-17-5; EC No. 200-578-6). In addition, the substance has a low predicted log Kow value of <3.
Ethanol is readily biodegradable and has very low log Kow.
Silicic acid condenses at concentrations above approximately 100-150 mg/L as SiO2 to give insoluble amorphous polysilicic acid. These hydrolysis products are inorganic substances which enter natural biogeochemical cycles.
Monosilicic acid is the bioavailable form of silica that can be absorbed by certain organisms in the environment. In these organisms, silicic acid, precipitated as insoluble amorphous silica, plays a structural and defensive role. In animals, silica is a trace nutrient.
- Reason / purpose for cross-reference:
- data waiving: supporting information
Reference
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
- Hazard assessment conclusion:
- no hazard identified
No hazard identified based on available repeated dose, reproductive and developmental toxicity data for synthetic amorphous silica.
No hazard identified based on available repeated dose, reproductive and developmental toxicity data for synthetic amorphous silica.
Data source
Materials and methods
Test material
- Reference substance name:
- Tetraethyl orthosilicate
- EC Number:
- 201-083-8
- EC Name:
- Tetraethyl orthosilicate
- Cas Number:
- 78-10-4
- Molecular formula:
- C8H20O4Si
- IUPAC Name:
- tetraethyl orthosilicate
Constituent 1
Results and discussion
Applicant's summary and conclusion
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.
Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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