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Administrative data

Link to relevant study record(s)

Description of key information

No studies are available. Based on molecular structure, molecular weight, water solibility, and octanol-water partition coefficient it can be expected that the submission substance is likely to be absorbed via the oral and dermal routes rather than via inhalation. Hydrolysis occurs rapidly, and systemic exposure is expected to both the parent substance and the hydrolysis product. Based on the water solubility, the registered substance and its silanol-containig hydrolysis product are likely to be distributed in the body, and excretion via the renal pathway can be expected. Bioaccumulation is not expected.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Toxicokinetic behaviour assessment for Triethoxy(phenyl)silane (CAS No: 780-69-8)

There are no studies available in which the toxicokinetic properties of triethoxy(phenyl)silane (780-69-8) have been investigated. Therefore, the toxicokinetic behaviour assessment of the substance and its hydrolysis product was assessed by its physico-chemical properties.

Triethoxy(phenyl)silane is a moisture-sensitive liquid that hydrolyses in contact with water (predicted half-life 1.5 hour at pH 7 and 20°C), generating ethanol and phenylsilanetriol. This therefore suggests that systemic exposure will be to the hydrolysis product rather than the parent substance. However, this toxicokinetic behaviour assessment will try to predict the behaviour of both. The toxicokinetics of ethanol is discussed elsewhere and is not included in this summary.

The molecular weight and the predicted water solubility of triethoxy(phenyl)silane are 240.38 g/mol and 50 mg/l, respectively. In contrast, the molecular weight and predicted water solubility of the hydrolysis product (phenylsilanetriol) is 156.21 g/mol and 1E+06 mg/l, respectively. This shows that the hydrolysis product is smaller in size and is more water soluble; therefore suggesting it has a greater potential to be absorbed than the parent substance. Furthermore, the predicted log Kow of 3.40 for the parent substance and -1.10 (at pH 7) for the hydrolysis product indicate that both substances are favoured to efficiently pass through biological membranes.

 

Absorption

 

Oral:

If absorption occurs, the hydrolysis of the parent substance in the low pH of the stomach will be rapid, so absorption of the parent substance is expected to be minimal and the hydrolysis product is more likely to be absorbed.

The predicted water solubility of 50 mg/l of the parent and 1E+06 mg/l of the hydrolysis products suggest that the latter will readily dissolve into the gastrointestinal fluids. Also, the low molecular weight (less than 200) of the hydrolysis product suggests it has the potential to pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water. Furthermore, the log Kow of 3.40 for the parent and -1.10 (at pH 7) for the hydrolysis product suggest that due to their moderate log Kow, the substances are favourable to be absorbed by passive diffusion.

 

Inhalation:

The vapour pressure of the parent substance (0.03 Pa) indicates that this substance has a low volatility, and therefore inhalation as a vapour is unlikely to occur. The very hydrophilic nature of the hydrolysis product suggest that it may be retained more efficiently within the mucus compared to the parent substance, however the moderate log kow (between -1 and 4) of the parent substance and hydrolysis product indicate that absorption directly across the respiratory tract epithelium by passive diffusion is possible.

 

Dermal:

The water solubility of 50 mg/l, log Kow of 3.40 and molecular weight of 240.38 g/mol of the parent substance suggest that absorption will be low. For the hydrolysis product (phenylsilanetriol) the water solubility of 1E+06 mg/l, log Kow value of -1.10 and molecular weight of 156.21 suggests the substance will also have a low potential to be absorbed by the dermal route, as it may be too hydrophilic to cross the lipid rich environment of the stratum corneum. QSAR based dermal permeability prediction (DERMWIN V2.00.2009) using molecular weight, log Kow and water solubility, calculated a dermal penetration rate of 0.00013 mg/cm2/h for triethoxy(phenyl)silane and 0.2055 mg/cm2/h for phenylsilanetriol, respectively. Since toxicity was observed in an acute dermal toxicity study, dermal absorption is possible for the test substance or its metabolites/degradation products.

 

Distribution

The low molecular weight (156.21) and very high water solubility of the hydrolysis product suggest it will diffuse through aqueous channels and pores more easily than the parent substance. The log Kow of -1.10 (at pH 7) indicates it is likely to be distributed into cells and therefore the intracellular concentration will be higher than the extracellular concentration. Also, the parent substance with the low to moderate water solubility (50 mg/l) and Log Kow (3.40) is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration. Accumulation in the body is not favourable for both substances.

 

Metabolism

Triethoxy(phenyl)silane is a moisture-sensitive liquid that hydrolyses rapidly in contact with water (predicted half-life 1.4 hour at pH 7 and 20°C), generating ethanol and phenylsilanetriol. There is no data on the metabolism of phenylsilanetriol. In the Ames test no difference was observed in the tests performed with or without metabolic activation. Due to the high water solubility no further metabolism is expected.

 

Excretion

The low molecular weight (below 300 g/mol) and good water solubility of the parent and hydrolysis product suggest that they are likely to be excreted by the kidneys into urine.