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Description of key information

No bioaccumulation potential was observed in the litterature.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
100
Absorption rate - dermal (%):
100
Absorption rate - inhalation (%):
50

Additional information

ABSORPTION

Oral / gastrointestinal absorption

With a low molecular weight (76.08 g/mol), high water solubility (330 g/L) and log Kow of 0.00, oral/gastrointestinal methylal absorption is favoured. Log Kow values between -1 and 4 are favourable for absorption by passive diffusion.

Oral absorption of methylal is set to 100% for risk assessment.

Inhalation absorption

Methylal high vapour pressure (40 kPa) indicates that the substance may be available for inhalation as a vapour. Its moderate log Kow value is favourable for absorption directly across the respiratory tract epithelium by passive diffusion. High solubility of methylal in water indicates that it may be retained within the mucus.

Methylal is a substrate of rat nose and liver cytochrome P-450-dependant-monooxygenase, an enzyme widespread in living organisms that metabolizes methylal in formaldehyde (Dahl & Hadley, 1983).

Inhalation absorption of methylal is set to 50% for risk assessment.

Dermal absorption

As a liquid with a molecular weight less than 100 g/mol, methylal dermal uptrake is favoured.

Based on molecular weight < 500 and log Kow in the (-1, 4) range, default dermal absorption of methylal is set to 100% for risk assessment.

Dermal absorption of methylal is set to 100% for risk assessment.

DISTRIBUTION

Tomilina et al. (1984) determinate the following correlation between methylal concentration in the air (y in mg/m3) and methylal concentration in rat's blood (x in mg/L) as y = 0.06 + 0.00008 x.

Once injected in dogs, methylal is transported by blood in which it is not detected after 24 hours (Virtue, 1951).

METABOLISM

Administration of methylal by oral route in rats for 3 consecutive mornings has no effects on kidney and liver histology, on hepatic drug-metabolized enzymes, urinaryformic acid excretion, hematological parameters and serum biochemical profiles. Methylal was found to be stable in rat artificial gastric juice at pH 2.5 to 9.0 for 24 hours at 37°C but unstable at lower pH (1.0, 1.3, 1.5, 1.7, and 2.0). The hydrolysis of 3.1 mM methylal at pH < 2.5 produced methanol and formaldehyde in a ratio of approximatively 2 to 1 (Poon et al., 2000). However, human stomach pH is 2.7 (1.8-4.5) and 1.9 (1.6-2.6) in median anterior and median posterior portion, respectively, and is 1.7 (1.4-2.1) when fasted (Zwart et al., 1999). As a consequence oral acute toxicity to methylal depends on its fate in stomach. At more, it seems that methylal is rapidely absorbed in the stomach.

EXCRETION

Excretion of methylal by lungs is the main elimination process in dogs: 87% and 1% of intravenous injected methylal is eliminated by exhalation and urine, respectively, within 7 hours.Methylal was not detected in exhaled air after 24 hours (Virtue, 1951).

The following values for absorption assessment were taken into account according to methylal behaviour (absorption, metabolism, distribution and elimination):

oral absorption of methylal is set to 100% for risk assessment;

inhalation absorption of methylal is set to 50% for risk assessment;

dermal absorption of methylal is set to 100% for risk assessment.

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