Trichloro-p-tolylsilane

Endpoint summary

Description of key information

No studies are available. Therefore, the toxicokinetic behaviour assessment of the substance and its hydrolysis product was assessed by its physico-chemical properties. Trichloro(4-methylphenyl)silane hydrolyses rapidly in contact with water, generating hydrogen chloride (HCl) and (4-methylphenyl)silanetriol. Based on molecular structure, molecular weight, water solibility, and octanol-water partition coefficient it can be expected that the hydrolysis product is likely to be absorbed via the oral and inhalation routes and to a lesser extent by dermal route. 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

There are no studies available in which the toxicokinetic properties of trichloro(4-methylphenyl)silane or its silanol hydrolysis product have been investigated. Therefore, the toxicokinetic behaviour assessment of the substance and its hydrolysis product was assessed by its physico-chemical properties.

Trichloro(4-methylphenyl)silane hydrolyses rapidly in contact with water, generating hydrogen chloride (HCl) and (4-methylphenyl)silanetriol. The substance would also hydrolyse rapidly in contact with moist skin; the resulting hydrolysis product, HCl, would be severely irritating or corrosive. This suggests that any systemic exposure will be to the hydrolysis product, (4-methylphenyl)silanetriol, rather than to the parent substance, trichloro(4-methylphenyl)silane. Hence, this toxicokinetic behaviour assessment will try to predict the behaviour of the hydrolysis product, (4-methylphenyl)silanetriol.

The molecular weight, predicted water solubility and log Kow of (4-methylphenyl)silanetriol are 170.2 g/mol, 520 mg/L and -0.6, respectively.

 

Absorption

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

 The predicted water solubility (520 mg/L) and molecular weight (170.2 g/mol) of the hydrolysis product (4-methylphenyl)silanetriol suggest it will readily dissolve in the gastrointestinal fluids and will have the potential to pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water, respectively.

 

Inhalation: The predicted vapour pressure of the parent (5.8 Pa) does indicate that inhalation as a vapour of the registered substance will be low. The predicted water solubility (520 mg/L) and low log Kow (-0.6) of the hydrolysis product suggest that absorption may be possible. There is no experimental data on the effects of acute or long-term inhalation exposure to the target substance.

 

Dermal: While the water solubility (520 mg/L) of the hydrolysis product favors dermal absorption, the low log Kow (-0.6) of the hydrolysis product suggests that the hydrolysis product is not likely to be sufficiently lipophilic to cross the stratum corneum, therefore dermal absorption is likely to be low. Moreover, QSAR based dermal permeability prediction (DERMWIN V2.00.2009) using molecular weight, log Kow and water solubility, calculated a dermal penetration rate of 3.689E-5 mg/cm²/h for the hydrolysis product, therefore, showing it will have low dermal penetration potential. However, the other hydrolysis product, HCl, is corrosive to the skin; damage to the skin might increase dermal penetration.

 

Distribution

Distribution of a compound within the body depends on the physico-chemical properties of the substance; especially the molecular weight, the lipophilic character and the water solubility. In general, the smaller the molecule, the wider is the distribution. If the molecule is lipophilic, it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration, particularly in fatty tissues (ECHA, 2017).

 As discussed under oral absorption, the hydrolysis product, (4-methylphenyl)silanetriol, is assumed to be absorbed after oral exposure. Therefore, the hydrolysis product absorbed from the GI tract will be transported via the portal vein to the liver, where further metabolism can take place. Substances that are absorbed through the pulmonary alveolar membrane or through the skin enter the systemic circulation directly before transport to the liver where metabolism will take place.

 

Metabolism

Trichloro(4-methylphenyl)silane hydrolysis rapidly in contact with water, generating hydrogen chloride (HCl) and (4-methylphenyl)silanetriol. There are no data regarding the enzymatic metabolism of trichloro(4-methylphenyl)silane or (4-methylphenyl)silanetriol.

 

Excretion

Due to low molecular weight (below 300 g/mol) and good water solubility it is assumed that the hydrolysis product will be mainly excreted via urine (ECHA, 2017).

 

Reference:

ECHA, 2017: Guidance on Information Requirements and Chemical Safety Assessment; Chapter R.7c: Endpoint specific guidance; Version 3.0; June 2017