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Description of key information

Magnesium methanolate rapidly hydrolyzes in aqueous environments. Toxicity is mediated by its degradation products MeOH and Mg(OH)2 and assessed for these products.

MeOH

Skin: not irritating (rabbit)

Eyes: not irritating (rabbit)

Mg(OH)2

Skin: not irritating based on two key in vitro studies

Eyes: not irritating (rabbit and in vitro)

Key value for chemical safety assessment

Additional information

MeOH

Skin:

The irritation potential of an unspecified dose of undiluted methanol in rabbits was examined under occlusive conditions after exposure intervals of 1, 5, and 15 minutes and 20 hours. According to Draize scoring, no signs of skin irritation were observed 24 hours and 8 days after treatment for any of the exposure time periods (BASF, 1975).

Eye:

One hour after instillation of 0.05 mL undiluted methanol into the eyes of two rabbits, slight erythemas and corneal opacity as well as moderate edemas associated with secretion were observed. After 24 hours, the effects were assessed as mild, and after 8 days the animals had no symptoms (BASF, 1975).

In another study, mild to moderate conjunctivitis and edemas as well as mild iritis were produced in six rabbits after instillation of 0.1 mL undiluted methanol into the eyes. Average scores after 24, 48, and 72 hours were approximately 2 for conjunctivae and < 1 for other effects. Primary irritation subsided after 72 hours, although redness of the conjunctivae persisted at that time. Information on effects after 8 and 14 days was not available (Jacobs, 1990).

Exposure of rats to an atmosphere saturated by methanol vapours at 20 °C produced severe irritation of mucous membranes and milky corneal opacity (time not specified) and eventually led to mortality of all animals within 8 hours (BASF, 1975). This was an additional observation and is not applicable for evaluation of irritant effects. Therefore, it is not relevant for classification.

Mg(OH)2

Skin:

Based on the two key studies, it is concluded that magnesium hydroxide is non-irritant in the in vitro skin irritation test.

In the first key study, the potential of magnesium hydroxide to induce skin irritation was tested using a human three-dimensional epidermal model. The possible skin irritation potential of magnesium hydroxide was tested using topical application for 15 minutes, followed by a 42 hour incubation period. Ten mg of magnesium hydroxide was added directly on top of the skin tissue, which was moistened with water. The mean relative tissue viabilities for magnesium hydroxide after 15 minutes of treatment were 91 %. Because the mean relative tissue viability for magnesium hydroxide was not below 50 % after the 3 minute treatment or 15 % after the 15 minute treatment, it was concluded that magnesium hydroxide is not a skin irritant under the conditions of this test.

In the second key study, the potential of magnesium hydroxide to induce skin corrision was tested using a human three-dimensional epidermal model. The possible corrosive potential of magnesium hydroxide was tested using topical application for either 3 minutes or 1 hour. Twenty five mg of magnesium hydroxide was added directly on top of the skin tissue, which was moistened with water. The mean relative tissue viabilities for magnesium hydroxide after 3 minute and 1 hour treatments were 88 % and 95 %, respectively. Because the mean relative tissue viability for magnesium hydroxide was not below 50 % after the 3 minute treatment or 15 % after the 1 hour treatment, it was concluded that magnesium hydroxide is not corrosive under the conditions of this test.

Eye:

According to the key study, since the mean in vitro irritancy score for magnesium hydroxide was below 55.1 after 240 minutes treatment, magnesium hydroxide is not classed as an irritant in the BCOP test. The study procedures were based on OECD guidelines. Magnesium hydroxide did not induce ocular irritation for both endpoints, resulting in a mean in vitro irritancy score of 5.1 after 240 minutes of treatment. Since this score is below 55.1 after 240 minutes treatment, magnesium hydroxide is not classed as an irritant in the BCOP test. An in vivo eye irritation test in rabbits did not reveal a degree of irritation that would lead to a classification as irritant to eyes.

Justification for classification or non-classification

Magnesium methanolate

Magnesium methanolate rapidly hydrolyzes in aqueous environments. Toxicity is mediated by its degradation products MeOH and Mg(OH)2 and assessed for these products.

Both hydrolysis products are not classified for irritation/corrosion. Based on the available information, magnesium methanolate thus does not have to be classified and has no obligatory labelling requirement for irritation/corrosion.

MeOH

Methanol exhibited no skin irritation in one reliable study. Available studies show that methanol is a slight to moderate eye irritant, but with reversibility of effects documented in one reliable study. High concentration of methanol vapours may be irritating to mucous membranes. Based on the vapour pressure of about 130 hPa at 20 °C, the molecular weight of 32 g/mol and the molar volume of about 24 L/mol, it can be estimated that the saturation concentration was ≥ 150 mg/L and, thus, clearly lethal.

In conclusion, methanol is not irritating to the skin and the eyes.

Mg(OH)2

An in vitro skin irritation study was performed on magnesium hydroxide and it was concluded that magnesium hydroxide is not irritating.

An in vitro skin corrosion study was also performed and it was concluded that magnesium hydroxide is not corrosive.

An in vitro and an in vivo eye irritation study were performed on magnesium hydroxide and it was concluded that magnesium hydroxide is not irritating.

Therefore, magnesium hydroxide is not classified as irritant or corrosive.