Registration Dossier

Administrative data

Link to relevant study record(s)

Description of key information

Key value for chemical safety assessment

Additional information

There are no in vivo data on the toxicokinetics of reaction mass of potassium methylsiliconate. The following summary has therefore been prepared based on the physicochemical properties of the substance itself and its condensation products. The substance is the potassium salt of methylsilanetriol and, due to its chemical properties, the commercial material unavoidably contains dimers and oligomers of methylsilanetriol. The absorption of the dimer and trimer following dermal and inhalation exposure is likely to be similar to that of the methylsilanetriol. Potentially human exposure can occur via inhalation, as dust, or dermal routes.

Absorption

Oral:

In contact with water reaction mass of potassium methylsiliconate is dissolving accompanied by the formation of KOH resulting in a high pH. Thus, significant oral exposure is not expected for this substance.

Dermal :

The molecular weight of methylsilanetriol (approximately 94) is favourable for dermal absorption. However, the water solubility (1 x 106 mg/L) and predicted log Kow (-2.5) of methylsilanetriol suggest that it is too hydrophilic to cross the lipid rich environment of the stratum corneum, and therefore dermal absorption into the blood is likely to be low. Dermal absorption of the dimer (log Kow -2.7) and trimer (log Kow 2.6) is expected to be similar. Since the pH of an aqueous solution is corrosive to the skin, damage to the skin might increase penetration. In the only available acute dermal toxicity study no significant clinical signs of toxicity were observed. There are no other studies to check for signs of dermal toxicity and therefore evidence of absorption.

Inhalation:

Reaction mass of potassium methylsiliconate may be inhaled as dust. In humans, particles with aerodynamic diameters below 100 μm have the potential to be inhaled, below 50 μm can reach the thoracic region and those below 15 μm can reach the alveolar region. Therefore when particles with an aerodynamic diameter below 15 μm are inhaled, they have the potential to be absorbed.

However, inhaled dust particles of reaction mass of potassium methylsiliconate, which is a highly water soluble substance, are likely to be retained in the mucous of the lungs. Reaction mass of potassium methylsiliconate is a multi-constituent substance containing methylsilanetriolate, dimers and oligomers of methylsilanetriolate, and potassium hydroxide. In contact with water the substance is only stable at high pH. As the pH is lowered, polymerisation occurs. Under comparable conditions of concentration and pH methylsilanetriolate is equivalent to the parent acid, methylsilanetriol. The log Kow of methylsilanetriol does not favour absorption across the respiratory tract epithelium. This mucous could be transported out of the respiratory tract, and possibly swallowed.

As with dermal exposure, damage to membranes caused by the corrosive nature of the aqueous solution might allow increased absorption of methylsilanetriol and the other constituents. There are no inhalation studies to check for signs of absorption.

Distribution

With very low log Kow and high water solubility, the hydrophilic nature of the methylsilanetriol molecule and its dimer and trimer will limit its diffusion across membranes (including the bloodbrain and blood-testes barriers) and its accumulation in fatty tissues.

Metabolism

There are no data regarding the metabolism of methylsilanetriol. Genetic toxicity tests in vitro showed no observable differences in effects with and without metabolic activation when solutions of potassium methylsilanetriolate or related substances were tested.

Excretion

The high water solubility of methylsilanetriol suggests that it is likely to be rapidly eliminated via the kidneys in urine as seen in a study by Varapreth et al. (1999) which describes the presence of methylsilanetriol in the urine of rats treated with D4. There is therefore no evidence to suggest that this substance will accumulate in the body.