Isobutyl methacrylate

Endpoint summary

Description of key information

Acute oral toxicity, rat, LD50=9590 mg/kg (Sterner and Stiglic, 1977)
Acute dermal toxicity > 5000 mg/kg (category read-across)
Acute inhalation toxicity, LT50 290 min at 29.74 mg/L (Lawrence et al. 1974)

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

9 590 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Dose descriptor:

LC50

Value:

29 740 mg/m³ air

Additional information

Data availability

For i-BMA a study is available for acute oral as well as acute inhalation toxicity. There are no valid data for dermal toxicity, but only two acute endpoints are required. By analogy to the isomer n-BMA it can be concluded that i-BMA is predicted to be of low acute dermal toxicity.

Oral route

In a study following an FDA guideline from 1959, which is equivalent to an OECD 401 guideline study, i-BMA was administered at doses ranging from 8880 to17760 mg/kg by intragastric intubation to fasted male and female rats (Sterner and Stiglic, 1977). Except for local effects at the site of first contact, haemorrhage in the intestinal tract, no target organ was identified. The LD50 was determined to be 9590 mg/kg, when administered as a single oral dose. Hence, the available data indicate that i-BMA is of low acute oral toxicity.

Inhalation route

In a screening study using male ICR mice the exposure time was determined which was lethal to half of the exposed animals (LT50; Lawrence et al. 1974).At the limit concentration of 29.74 mg/L (5029 ppm) average survival time was 290 min. Hence, this dose is also comparable to an LC50 in a standard inhalation test.In an inhalation study (Jones, 2002) in F344 rats, using specialist histopathology techniques to study the nasal tissues, isobutyl methacrylate did not produce lesions in the olfactory region of the nasal cavity, the target for methacrylate esters, following exposure at 200 ppm for 6 hrs. The available data indicate that all members of the category, i-BMA included, are of low acute inhalation toxicity. The vapour pressure of the esters drops markedly across the category such that already in the case of the butyl esters the observed toxicity is above the saturated vapour pressure as indicated by the fact that the studies were performed with mixtures of vapour and mist.

Dermal route

There is also a early pre-guideline studies of limited reliability available in guinea pigs for i-BMA that indicate low acute dermal toxicity. By analogy to other esters in the category, low dermal toxicity of i-BMA is predicted.

Justification for classification or non-classification

According to the available data and CLP as well as US-GHS(2009) criteria, no classification is warranted for acute toxicity.