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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Link to relevant study record(s)

Description of key information

No studies are available. Based on molecular structure, molecular weight, water solubility, and octanol-water partition coefficient it can be expected that the submission substance is likely to be absorbed via the oral, dermal, and inhalation routes. 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-containing 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 measured data on the toxicokinetics of dimethoxy(dimethyl)silane.

The following summary has therefore been prepared based on the predicted and measured physicochemical properties of the registered substance and its hydrolysis product (see Table below). The data have been used in algorithms which are the basis of many physiologically based pharmacokinetic and toxicokinetic (PBTK) prediction models. Although these algorithms provide quantitative outputs, for the purposes of this summary only qualitative statements or predictions will be made because of the remaining uncertainties that are characteristic of prediction models.

The main input variable for the majority of the algorithms is the log Kow. By using this and, where appropriate, other known or predicted physicochemical properties of dimethoxy(dimethyl)silane or its hydrolysis product, reasonable predictions or statements may be made about their potential absorption, distribution, metabolism and excretion (ADME) properties.

Dimethoxy(dimethyl)silane hydrolyses rapidly in contact with water (measured half-life less than 0.6 hours at pH 7 and at 25°C), generating dimethylsilanediol and methanol. Direct exposure of workers and the general population to the parent substance or its hydrolysis products might occur via the inhalation and dermal routes. Exposure of the general population via the environment might occur via the oral route but would be limited to the hydrolysis product due to the rapid hydrolysis.

The toxicokinetics of methanol have been reviewed in other major reviews and are not considered further here.

Table: Physicochemical properties

Physicochemical properties





Water solubility

9200 mg/L at 20-25 °C (QSAR)

1.0E+06 mg/L at 20-25 °C (QSAR)

Vapour pressure

8660 Pa at 20°C and 20500 Pa at 40°C (OECD 104)

7 Pa at 25°C (QSAR)

Log Kow

2 (QSAR)

-0.41 (QSAR)

Molecular weight (g/mol)




<0.6 hour at pH 7 and at 25°C (OECD 111)





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 to be 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 (ECHA, 2017).

Therefore, if oral exposure to parent did occur, molecular weight of dimethoxy(dimethyl)silane (120.22 g/mol) is in the favourable range and would favour absorption, so systemic exposure by this route is likely. At pH 2 in the stomach, the parent compound is predicted to hydrolyse into the hydrolysis product dimethylsilanediol within 5 seconds at the temperature of 37.5°C. Dimethylsilanediol has a favourable molecular weight and water solubility values for absorption so systemic exposure to this would also be likely.

Signs of systemic toxicity were evident in the repeated dose toxicity (Dow, 2010 and BSL, 2020) oral studies as well as in the reproduction/developmental dose range finding toxicity screening study (CRL, 2022), which indicates systemic exposure to either the parent and/or hydrolysis product.



If dermal exposure were to occur, in practice this would be to the parent compound as well as the hydrolysis product.

The water solubility of 9200 mg/L, log Kow of 2 and molecular weight of 120.22 g/mol of the parent substance suggest that absorption is moderate to high. For the hydrolysis product dimethylsilanediol the water solubility of 1E+06 mg/L, log Kow value of -0.41 and molecular weight of 92.17 suggests the substance will 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 64.65 µg/cm²/h for dimethoxy(dimethyl)silane and 258.97 µg/cm²/h for dimethylsilanediol, respectively.



The vapour pressure of the parent substance (8660 Pa) indicates that this substance has a high volatility, and therefore inhalation as a vapour is likely 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.

The pH of the airway surface liquid has been determined to be in the range 6.7-7 (Jayaraman et al., 2000), without significant inter- or intraspecies variation.

The measured hydrolysis half-life at 20-25 °C and pH 7 (relevant for lungs and blood) is lower than 0.6 hours. As the hydrolysis reaction may be acid or base catalysed, the rate of reaction is expected to be slowest at around pH 7 and increase as the pH is raised or lowered. For an acid-base catalysed reaction in buffered solution, the measured rate constant is a linear combination of terms describing contributions from the uncatalyzed reaction as well as catalysis by hydronium, hydroxide, and general acids or bases.

kobs= k0+ kH3O+[H3O+] + kOH-[OH-] + ka[acid] + kb[base]

Hydrolysis is a chemical reaction that is independent of enzymatic involvement. It is reasonable to assume that the parent and hydrolysis products of dimethoxy(dimethyl)silane will be present in the airway surface liquid, without significant variation between individuals.

Proving the hydrolysis rate in the lungs of experimental animals in vivo would present many complicated (possibly insurmountable) technical difficulties, and therefore the presence of parent and hydrolysis product is assumed as a worst-case scenario.

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’s Law coefficient and the octanol: air partition coefficient (Koct: air) as independent variables.

Using these values for dimethoxy(dimethyl)silane predicts a blood: air partition coefficient of approximately 8:1 meaning that, in steady state, more or less 90% of this substance will be in blood and very little in air, and therefore if lung exposure occurs the majority of parent substance available would be absorbed. However, hydrolysis is expected. For the hydrolysis product, dimethylsilanediol, the predicted blood: air partition coefficient is approximately 8.2E+5:1 meaning that systemic exposure is even more likely. Again, this prediction is based on physicochemical properties and is not expected to vary between individuals.

It is also important to consider the water solubility of dimethoxy(dimethyl)silane and its hydrolysis product with respect to dissolving in the mucous of the respiratory tract. The parent is expected to hydrolyse in the aqueous mucous. The hydrolysis product is highly soluble in water and therefore expected to be present in the mucous lining following inhalation of dimethoxy(dimethyl)silane, from which there is potential for passive absorption.



The low molecular weight, high and very high water solubility of the parent and hydrolysis product, respectively, suggest they will both have the potential to diffuse through aqueous channels, pores and will be widely distributed; however the log Kow of ‐0.4 for dimethylsilanediol indicates it is unlikely to be distributed into cells. Therefore, the extracellular concentration will be higher than the intracellular concentration. Conversely, the log Kow (2.0) of the parent product suggests it is lipophilic enough to distribute into cells and therefore the intracellular concentration will be higher than the extracellular concentration.

The high water solubility and the moderate log Kow of both the parent and hydrolysis product suggest that accumulation in the body is not likely for both substances.

For blood: tissue partitioning a QSPR algorithm has been developed by DeJongh 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. Using this value for dimethoxy(dimethyl)silane (log Kow = 2.0) predicts that, should systemic exposure occur, distribution would primarily be into fat, with potential distribution into liver, muscle, brain and kidney but to a much lesser extent.

For the hydrolysis products, distribution into the main body compartments is predicted to be minimal.

Table: Tissue: blood partition coefficients


Log Kow

























Dimethoxy(dimethyl)silane is a moisture-sensitive liquid that hydrolyses rapidly in contact with water (measured half-life less than 0.6 hours at pH 7 and 25°C), generating methanol and dimethylsilanediol. There is no data on the metabolism of dimethylsilanediol. In the in vitro mammalian mutagenicity assay, genotoxicity was observed in presence of metabolic activation indicating that some kind of metabolisation occurred.

Dimethoxy(dimethyl)silane is within an analogue group of substances for which, in general, there is no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account (PFA, 2013f. This observation is supported by studies with dimethylsilanediol that shows no evidence of biodegradation (Gerin, 2016, for details please refer to Section 5.2 of the dossier). It is therefore concluded that the substance and its silanol hydrolysis product are not recognised by biological systems containing all the mammalian enzymes and metabolic systems.



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

A determinant of the extent of urinary excretion is the soluble fraction in blood. QPSRs as developed by DeJongh et al. (1997) using log Kow as an input parameter, calculate the solubility in blood based on lipid fractions in the blood assuming that human blood contains 0.7% lipids.

Using the algorithm, the soluble fraction of dimethoxy(dimethyl)silane in blood is approximately 60% and of dimethylsilanediol is approximately 100%. Therefore, these figures suggest that the hydrolysis product is likely to be effectively eliminated via the kidneys in urine but the parent substance would be predicted to be eliminated from the body to a lesser extent via the kidneys.




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

DeJongh, J., H.J. Verhaar, and J.L. Hermens, A quantitative property-property relationship (QPPR) approach to estimate in vitro tissue-blood partition coefficients of organic chemicals in rats and humans. Arch Toxicol, 1997.72(1): p. 17-25.

Gerin (2016) Fate of silanols in various aquatic / soil environments: Investigation of dimethylsilanediol (bio)degradation in microcosms

Jayaraman, S.; Song, Y.; Vetrivel, L.; Shankar, L. & Verkman, A. Noninvasive in vivo fluorescence measurement of airway-surface liquid depth, salt concentration, and pH Journal of Clinical Investigation, American Society for Clinical Investigation, 2000, 107, 317-324.

Meulenberg, C.J. and H.P. Vijverberg, Empirical relations predicting human and rat tissue:air partition coefficients of volatile organic compounds. Toxicol Appl Pharmacol, 2000. 165(3): p. 206-16.

PFA, 2013f, Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007