2-methylbutene

Endpoint summary

Description of key information

Based on assessment of the available data for 2-methyl-2-butene (2M2B), the oral LD50 of isoamylene is in the range of 1000 to 1700 mg/kg.  The dermal LD50 is >2000 mg/kg.  The 4-hour LC50 is >175,000 mg/m3.  Inhalation of isoamylene can produce central nervous system depression, anaesthesia and/or asphyxiation that are reversible following cessation of exposures. 

Additional information

The acute toxicity of isoamylene has been determined from studies on the main component, 2-methyl-2-butene (2M2B) which has a low order of acute toxicity in animals by the dermal and inhalation routes of exposure.  It is classifiable as harmful by the oral route of exposure.

Non-human data

Oral

In order to determine the acute oral LD50 of 2M2B a range-finding and definitive study have been performed in albino Wistar rats.

In the definitive study, groups of six males and six females were dosed with 1.0, 1.6, 2.5, 4.0, 6.3 and 10 ml/kg. The majority of deaths occurred within the first 3 days following dosing and most survivors had recovered from signs of intoxication by the third day. The author estimated the oral LD50 to be in the range of 1 to 4 ml/kg (i.e., 700 to 2600 mg/kg) (SRC, 1980).  Further inspection of the data (OECD SIDS, 2005) allows this to be refined to a range of 1.6 to 2.5 mL/kg (1000 to 1700 mg/kg).

Dermal

In order to determine the acute dermal LD50 of 2M2B range-finding and definitive studies have been performed in albino Wistar rats.  The acute dermal LD50 value of 2M2B is >2000 mg/kg (SRC, 1980).

Inhalation

In a limit test, groups of 5 male and 5 female albino Wistar rats were exposed for 4 hours to a test atmosphere containing 61000 ppm (175,000 mg/m³) of 2M2B.  Inhalation of 2M2B can produce symptoms of central nervous system depression, anaesthesia and/or asphyxiation that are reversible following cessation (within 3 minutes) of exposures. There were no deaths and macroscopic and microscopic examination at necropsy of animals killed 14 days post-exposure revealed no compound related effects.  The acute 4 hours inhalation LC50 of 2M2B in rats is >175,000 mg/m³ (SRC, 1982).

Studies in Humans

No data are available

 

Justification for classification or non-classification

The acute oral LD50 has been concluded to be in the range of 1000 – 1700 mg/kg and therefore isoamylene should be classified as Xn, R22 under DSD with the equivalent classification of Category 4,H302: Harmful if swallowed under CLP.

 

Based on assessment of the available data for 2M2B, isoamylene does not warrant classification under DSD or CLP for acute dermal and inhalation toxicity. No classification for narcotic effects of vapour is required under DSD as this relates to effects observed at <20000 mg/m³. In relation to classification under CLP, a Category 3 STOT SE applies: H336: May cause drowsiness and dizziness (relating to the acute oral data).

 

Aspiration is a known hazard of hydrocarbons and, although there is no evidence of aspiration hazard from the animal studies considered, classification is based on the physical characteristics of isoamylene/2M2B which has a kinematic viscosity below the cut off values for DSD of 7mm²/s and for CLP of 20.5 mm²/s for hydrocarbons and therefore classification is warranted. Classification as Xn; R65 Harmful; Harmful: may cause lung damage if swallowed under DSD and Cat1H304 May be fatal if swallowed and enters airways is warranted.