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PBT assessment

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PBT assessment: overall result

2-methylbutane (Isopentane)
Type of composition:
boundary composition of the substance
State / form:
Reference substance:
2-methylbutane (Isopentane)
PBT status:
the substance is not PBT / vPvB

Persistence (P) Assessment

A substance is not considered to be persistent if it can be demonstrated that it has potential to degrade (via photolysis, hydrolysis and/or biodegradation) 

The key study for the biodegradation of 2-methylbutane (ExxonMobil Chemical 117594A 1996) is a non-GLP study which followed guidelines equivalent to OECD guideline 301F manometric respirometry test. There were some minor deviations in test concentrations from the protocol, however these deviations were shown to not affect the integrity of the study as it meet the validity criteria. The study was therefore deemed suitable for assessment. This study indicates that 2 -methylbutane is readily biodegradable.

Simulation testing was not required as 2-methylbutane is readily biodegradable.

Bioaccumulation (B) Assessment

If the substance has a log Kow lower than 4.5 and no specific mechanism of uptake apart from hydrophobic partitioning is known and the possibility for accumulation in other food chains than the aquatic food chain can be ruled out, then the substance can be considered as not B and not vB.

2 -methylbutane has a reported log Kow of 4. Therefore, 2-methylbutane can be considered not B and not vB.

Toxicity (T) Assessment: As 2-methylbutane is not classified as persistent or bioaccumulative, a toxicity assessment is not required.

Human Health Hazards Assessment (T)


According to REACH Annex X, this study does not need to be conducted because the substance is not classified as mutagen category 3 and there is no evidence from the repeated dose studies that the substance is able to induce hyperplasia and/or pre-neoplastic lesions.


All in vitro genetic toxicity studies (i. e., gene mutation studies in bacteria and cytogenicity studies in mammalian cells) from 2 -methylbutane and n-pentane showed negative results. In vivo mouse micronucleus studies with n-pentane also produced no evidence of mutagenic effects. Based on the weight of evidence, 2 -methylbutane is unlikely to be mutagenic and does not meet the criteria for classification and labelling as described in the CLP EU Regulation 1272/2008.

Reproductive Toxicity:

THere are no reproductive toxicity data available for 2 -methylbutane. Data for read-across pentane was used.

With a maternal and developmental NOAEL of 1000 mg/kg/day, n-pentane showed no maternal or developmental treatment-related effect and does not meet the criteria for classification as either a maternal or developmental toxicant. Therefore, pentane does not meet the criteria for classification as either a maternal or developmental toxicant under CLP EU.

Conclusion of PBT/vPvB assessment

Based on 2-methylbutane avaialable information and on read-across to n-pentane, 2-methylbutane can be considered readily biodegradable and therefore is not considered P or vP. Also, based on a reported log Kow of 3.82, 2,2-dimethylbutane is not considered B or vB. As such an assessment for T (toxicity) is not required for 2-methylbutane and it is not classified as PBT or vP/vB.