Butene

Endpoint summary

Description of key information

Members of the butenes category are flammable gases at room temperature and therefore the requirement for data on acute oral and dermal toxicity is waived in accordance with REACH Annex XI. Members of the butenes category have low acute inhalation toxicity. The LC50 for 2-butene is excess of 10,000 ppm (22,948 mg/m3).

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The requirement for data on acute oral and dermal toxicity is waived in accordance with REACH Annex XI, as members of the butenes category are flammable gases at room temperature. Members of the butenes category have low acute inhalation toxicity. The acute inhalation toxicity of 2-butene has been determined in a key OECD 403 guideline study. An LC50 in excess of 10,000 ppm (22,948 mg/m³) (the lower explosive limit) after 4h inhalation exposure was reported. No clinical signs were seen and normal growth occurred over the 14 day observation period. No abnormalities were observed at gross necropsy. Only one concentration of 2-butene was tested (TNO 1992a). The low acute toxicity of 2-butene by inhalation is consistent with the low acute inhalation toxicity of 2-methylpropene. LC50s in rats of 620,000 mg/m3 (4h exposure) and mice 415,000 mg/m3 (2h exposure) respectively were reported for 2-methylpropene (Shugaev 1969). These results are also supported by data from Virtue (1950). 1-Butene, cis and trans 2-butene and 2-methylpropene at 27.2, 25.5, 21 and 32% (approximately 623,000; 580,000, 480,000 and 734,000mg/m3) respectively produced respiratory arrest in mice after exposure for 10 min. No clinical observations were seen, other than narcosis, during or after exposure. The butenes have the potential to produce narcosis or cause asphyxia by reducing the available concentration of oxygen at butene concentrations above the lower explosive limit.

There are no acute toxicity data in humans.

Justification for selection of acute toxicity – inhalation endpoint
No deaths have occurred in experimental animals exposed to butenes up to the lower explosion limit. While some studies have indicated asphyxia and death at higher concentrations, methodological or reporting limitations call into question the derivation of an LC50. In any case, such a value would be meaningless with respect to explosion hazard, and is beyond the threshold for classification for acute toxicity.

Justification for classification or non-classification

Members of the butenes category are flammable gases at room temperature and therefore inhalation exposure is the only relevant route. Category members are of low acute toxicity by the inhalation route with LC50 values in excess of 10,000 ppm (22,948 mg/m3) (the lower explosive limit). Category members therefore do not warrant classification under GHS/CLP.