Reaction mass of butane and butene

Endpoint summary

Additional information

There is no data available on genetic toxicity of "Reaction mass of butane and butene". Below we present an assessment of the data for each of the single components Butene, 2 -methylpropene, butane, isobutane and 1,3 -butadiene which are present in "Reaction mass of butane and butene".

Butene/2-methylpropene:

Members of the butenes category are not genotoxic. Key bacterial mutation studies (Ames tests) on all isomers (butene, but-1-ene, 2-butene and 2 -methylpropene) are provided by Araki (1994) and a key study on 2-butene is provided by Safepharm (1992a). Supporting studies on 2 -methylpropene are provided by Cornet et al (1992), NTP (1998) and Shimizu et al et al (1985). In all studies, all category members were not mutagenic in the presence and absence of metabolic activation whilst positive control compounds gave the expected results demonstrating that the studies were robust.

2-Butene has been tested in vitro in a chromosome aberration study (Safepharm 1992b) where it was not clastogenic to rat lymphocytes in vitro in the presence and absence of metabolic activation.2-Methylpropene also gave negative results in vitro; a micronucleus assay in human lymphocytes (Jorritsma et al 1995) and a mouse lymphoma mutation assay (IRI 1981a) were both negative.In addition, a mammalian cell transformation assay on 2-methylpropene (IRI 1981b) was also negative in the presence and absence of metabolic activation. In all cases, positive control compounds gave the expected results, demonstrating that the studies were robust.

Genotoxicity studies in vivo are provided by a key bone marrow micronucleus assay on 2-methylpropene (Exxon 1990) where mice were exposed to concentrations up to 10,000 ppm (22,948 mg/m3) for 2 days. A statistically significant increase in micronucleus formation in mouse bone marrow was not observed therefore 2-methylpropene was not clastogenic in mouse bone marrow. A peripheral blood micronucleus test was also conducted during a repeat dose toxicity test on 2-methylpropene, where mice were exposed via inhalation for 14 weeks at 500, 1000, 2000, 4000 and 8000 ppm (1147, 4589, 18,359 mg/m3). No increases in the frequency of micronucleated normochromatic erythrocytes were seen in peripheral blood samples in either sex (NTP 1998).

When the overall database on the genotoxicity of all the butene isomers in this category are considered together with the negative carcinogenicity studies on 2-methylpropene in rats and mice there is minimal likely-hood of genotoxicity for any of the category members.

There is no data on the genetic toxicity of the butenes in humans.

Butane/isobutene:

Methane CAS Number 74-82-8

In vitro data

The key study is considered to be a bacterial mutation assay (NTP, 1993), a recognised core assay type for investigating mutation in vitro.

Methane was tested in a standard Ames test but using gas chambers to allow appropriate examination of a gaseous material. Salmonella typhimurium (TA1535, TA97, TA98 and TA100) was treated with methane both with and without auxiliary metabolic activation (S9). A range of doses of methane was used, and the S9 was prepared from both rat and hamster livers and added at two levels.

Methane was not mutagenic in this test system.

In vivo data

No in vivo genotoxicity data are available for methane.

Human information

There is no information indicating any adverse effects of methane.

 

Summary

Methane has been examined for mutagenicity in vitro in the Ames test using a test system that is suitable for examining gaseous materials. It was tested both in the absence and presence of different levels of S9 fractions from both rat and hamster. It was non-mutagenic in the assay. This result is what would be expected from the simple chemical structure of methane. There are no functional groups in the molecule, and it would not be expected to undergo significant metabolism to any reactive species. It carries no alerts for possible genotoxic activity based on established Structure Activity Relationship (SAR) principles ( Tennant RW and Ashby J (1991). Classification according to chemical structure, mutagenicity to Salmonella and level of carcinogenicity of a further 39 chemicals by the US National Toxicology Program.  Mutat Res 257 (3) 209-227). 

 

Ethane CAS Number 74-84-0

No data were identified. There are no functional groups in the ethane molecule, and it would not be expected to undergo significant metabolism to any reactive species. It carries no alerts for possible genotoxic activity based on established Structure Activity Relationship (SAR) principles (Tennant and Ashby, 1981). 

 

Propane CAS Number 74-98-6

In vitro data

The key study is considered to be a bacterial mutation assay (Kirwin et al, 1980), a recognised core assay type for investigating mutation in vitro.

Propane was tested in a standard Ames test but using gas chambers to allow appropriate examination of a gaseous material. Salmonella typhimurium (TA1535, TA1537, TA1538, TA98 and TA100) was treated with propane both with and without auxiliary metabolic activation from rat liver (S9). A range of doses of propane was used, up to 50% atmosphere. Propane was not mutagenic in this test system.

In vivo data

No in vivo genotoxicity data are available for propane.

Human information

There is no information indicating any adverse effects of propane.

Summary 

Propane has been examined for mutagenicity in vitro in the Ames test using a test system that is suitable for examining gaseous materials. It was tested both in the absence and presence of different levels of S9 fractions from both rat and hamster. It was non-mutagenic in the assay. This result is what would be expected from the simple chemical structure of propane. There are no functional groups in the molecule, and it would not be expected to undergo significant metabolism to any reactive species. It carries no alerts for possible genotoxic activity based on established Structure Activity Relationship (SAR) principles (Tennant and Ashby, 1981). 

 

Isobutane CAS Number 75-28-5

In vitro data

The key study is considered to be a bacterial mutation assay (Kirwin et al, 1980), a recognised core assay type for investigating mutation in vitro.

Isobutane was tested in a standard Ames test but using gas chambers to allow appropriate examination of a gaseous material. Salmonella typhimurium (TA1535, TA1537, TA1538, TA98 and TA100) was treated with isobutane both with and without auxiliary metabolic activation from rat liver (S9). A range of doses of isobutane was used, up to 50% atmosphere. Isobutane was not mutagenic in this test system.

In vivo data

No in vivo genotoxicity data are available for isobutane.

Human information

There is no information indicating any adverse effects of isobutane.

 

Summary

Isobutane has been examined for mutagenicity in vitro in the Ames test using a test system that is suitable for examining gaseous materials. It was tested both in the absence and presence of different levels of S9 fractions from both rat and hamster. It was non-mutagenic in the assay. This result is what would be expected from the simple chemical structure. There are no functional groups in the molecule, and it would not be expected to undergo significant metabolism to any reactive species. It carries no alerts for possible genotoxic activity based on established Structure Activity Relationship (SAR) principles (Tennant and Ashby, 1981). 

 

Butane CAS Number 106-97-8

In vitro data

The key studies are considered to be bacterial mutation assays (Kirwin et al 1980, NTP, 2005), and an in vitro cytogenetic assay (Safepharm, 2008). These are recognised core assay types for investigating mutation in vitro.

Butane was tested in a standard Ames test but using gas chambers to allow appropriate examination of a gaseous material (Kirwin et al 1980). Salmonella typhimurium (TA1535, TA1537, TA1538, TA98 and TA100) was treated with butane both with and without auxiliary metabolic activation from rat liver (S9). A range of doses of butane was used up to a dose of 50% atmosphere.  In a second Ames test, Salmonella typhimurium (TA1535, TA97, TA98 and TA100) was treated with butane both with and without auxiliary metabolic activation (S9). In this study, a range of doses of butane was again used, and the S9 was prepared from both rat and hamster livers and added at two levels. Butane was not mutagenic in either of these studies.

Butane was examined in an in vitro cytogenetic assay in human lymphocytes in both the absence and presence of auxiliary metabolic activation. It was tested using contained exposures to allow appropriate examination of a gaseous material. Butane was not mutagenic in this assay.

In vivo data

No in vivo genotoxicity data from mammalian systems are available for butane. Butane has been examined in the Sex Linked Recessive Lethal assay in drosophila, at a dose level of 35% atmosphere (NTP, 2005). The material was reported to give a negative response.

Human information

There is no information indicating any adverse effects of butane.

 

Summary

Butane has been examined for mutagenicity in vitro in the Ames test using a test system that is suitable for examining gaseous materials. It was tested both in the absence and presence of different levels of S9 fractions from both rat and hamster. It was non-mutagenic in the assay.   Furthermore, butane has been examined in an in vitro cytogenetic assay in human lymphocytes to current OECD guideline standards, again under exposure conditions appropriate for a gaseous material. It was negative in this assay. Butane has therefore been examined, and found to be negative, for both gene mutation and cytogenetic endpoints in vitro. This result is what would be expected from the simple chemical structure of butane. There are no functional groups in the molecule, and it would not be expected to undergo significant metabolism to any reactive species. It carries no alerts for possible genotoxic activity based on established Structure Activity Relationship (SAR) principles (Tennant and Ashby, 1981).

 

 

Petroleum gases, liquefied,

In vitro/vivo data

The major constituents are identified as propane and propene.

HLS (2009) assessed the potential inhalation toxicity of liquified petroleum gas when administered via whole-body exposures to rats for 13 weeks. The assessment included evaluations of genotoxicity parameters.

Rats were exposed for six hours per day to 0 (air control), 1000, 5000 or 10000 ppm of LPG for 5 days per week for 13 consecutive weeks (highest exposure concentration was selected for safety reasons and approximated 50% of the lower explosive limit). At the end of the treatment period, all animals were euthanized and necropsied and the incidences of micronucleated immature erythrocytes were calculated in 5 males & females per dose concentration. After 13 weeks of exposure, there were no treatment-related differences in micronucleus incidence at concentrations up to 10000 ppm, compared to the air control animals. The no observed adverse effect concentration (NOAEC) was 10000 ppm.

Summary for the category

In summary, simple short chain alkanes (i.e methane, ethane, propane, butane, isobutane) can be considered in a similar manner, and data are available for methane, propane, butane and isobutane in the Ames test, testing under exposure conditions appropriate for gaseous materials, that similarly show them to be non-mutagenic. Furthermore, butane (the C4 analogue alkane) has been examined in an in vitro cytogenetic assay in human lymphocytes to current OECD guideline standards, again under exposure conditions appropriate for a gaseous material. It was negative in this assay. The data are further supported by in vivo data on liquefied petroleum gases (major constituents identified as propane and butane). After 13 weeks of exposure of rats, there were no treatment-related differences in micronucleus incidence at concentrations up to 10000 ppm, compared to the air control animals.

The available data for the short-chain alkanes indicates no genotoxic activity across endpoints of bacterial gene mutation, in vitro clastogenicity and in vivo.

 

1,3-butadiene:

In Vitro Studies

 

The key studies are considered to be bacterial mutation assays (Araki et al 1994, Madhusree et al 2002) and a mammalian cell cytogenetic assay (Asakura et al 2008).  These are two recognised core assay types for investigating mutation in vitro. 

1,3-Butadiene was tested in a standard Ames test and with exposure to the chemical contained in gas bags. S. typhimurium (TA1535, TA1537, TA98 and TA100) and E. coli (WP2 uvrA and WP2P uvrA) were treated with 1,3-butadiene both with and without auxiliary metabolic activation from rat liver (S9) at concentrations up to 50% in the atmosphere. Positive results were obtained in Salmonella strain TA1535 in the presence of S9 in both studies, and a limited response in TA100 in one study (Araki et al 1994). Negative results were obtained in the absence of S9. Similar positive responses in the presence of S9 have been reported by other investigators (EU RAR, 2002). 1,3-Butadiene is mutagenic in bacterial gene mutation assays. Asakura et al (2008) examined 1,3-butadiene in an in vitro cytogenetic assay with CHL cells in both the absence and presence of S9. The test system was designed to allow a contained exposure to gaseous materials and concentrations up to 20% 1,3-butadiene were used. An increase in the frequency of chromosomal aberrations was observed, and a positive response reported both in the absence and presence of S9. The positive response in the absence of S9 is not consistent with the Ames test results but nevertheless the overall result indicates that 1,3 -butadiene is clastogenic in mammalian cells in vitro.

 

There are additional reports of positive responses in mammalian cell gene mutation assays, but due to protocol or reporting deficiencies these are considered unreliable (EU RAR 2002). The REACH requirement for an adequate in vitro gene mutation study in mammalian cells is waived, as adequate data are available from in vivo gene mutation tests (Column 2 adaptation). Conflicting responses have been reported in studies examining for the endpoint of sister chromatid exchange (EU RAR 2002). 1,3-butadiene is considered to be mutagenic in vitro.

 

 

In Vivo Studies – Non-Human Information 

 

The key studies are considered to be somatic cell cytogenetic and gene mutation studies in the mouse (Adler et al 1994, Cunningham et al 1986, Cochrane and Skopek 1994), and dominant lethal studies in the mouse (Adler et al 1994, Brinkworth et al 1998) and the rat (Hughes et al 1996). These are recognised core assay types for investigating mutation in vivo.

 

The induction of micronuclei in bone marrow and peripheral blood erythrocytes was investigated in mice by Adler et al 1994). Adult (102/E1xC3H/E1)F1 mice were exposed to 0, 50, 200, 500 or 1,300 ppm (110, 442, 1106 or 2876 mg/m3) 1,3-butadiene, 6 hours/day for 5 days and bone marrow and blood samples taken 18-24 hours after the last exposure. There was a statistically significant increase in the frequency of micronucleated cells in the bone marrow and peripheral blood at all exposure concentrations. It was also observed that male mice were more sensitive than females at the higher exposure levels. Similar positive results in the mouse bone marrow micronucleus test were obtained by Cunningham et al (1986). Male B6C3F1 mice were exposed to 1,3-butadiene at concentrations of from 10 to 10,000 ppm (22-22126 mg/m3) (6h/day for 2 consecutive days). A significant dose-dependent increase in micronuclei induction was observed at concentrations of 100 ppm (221 mg/m3) and above.

The ability of 1,3-butadiene to cause gene mutation in vivo was investigated at the hprt locus in splenic T cells in male B6C3F1 mice (Cochrane and Skopek 1994). Animals were exposed to 0 or 625 ppm (1383 mg/m3) 1,3-butadiene for 6 hours/day, 5 days/week for 2 weeks and sacrificed 2 weeks later. Splenic T cells were isolated and cultured for 10 days to allow growth of mutant hprt- colonies. A statistically significant increase in mutation frequency to 5 times the control value was observed. It was concluded that repeated exposure to 1,3-butadiene causes gene mutations in mice. Age and gender dependent differences in 1,3-butadiene-induced mutagenicity were investigated at the hrtp locus in splenic T cells in mice (Meng et al, 2007). Values obtained in this study were compared with those obtained in previous studies (Meng et al 1998, 1999, Walker and Meng 2000). To investigate age differences, female mice aged 8-9 weeks or 4-5 weeks were exposed to 1250 ppm (2765 mg/m³)(6 h/day, 5 days/week) of 1,3- butadiene for 2 weeks. 1,3- butadiene was mutagenic to mice and both ages had similar mutagenic potencies although the shape of the curves was different. To investigate sex differences, mice aged 4-5 weeks were exposed to 1250 ppm of 1,3-butadiene for 2 weeks. Mutation frequencies in treated males were 6.2-fold greater than in control males whilst the figure in female mice was 2.3-fold higher than that in males. Female mice are therefore more susceptible to 1,3-butadiene-induced hrpt mutations than male mice

 

There are a number of further reports of positive results for 1,3-butadiene in mice including both cytogenetic studies and gene mutation studies (EU RAR 2002). Adler et al 1994 and Cunningham et al (1986) provide examples. In a positive mouse spot test, pregnant female mice were exposed to 1,3-butadiene at 500 ppm (1106 mg/m3), 6h/day from days 8 -12 of gestation. An increased incidence of coat colour spots of genetic relevance were found in offspring (Adler et al 1994). Male B6C3F1mice were exposed to 1,3-butadiene by inhalation, at concentrations from 10 to 10,000 ppm (22-22,126 mg/m3), 6h/day, for 2 consecutive days in a sister chromatid exchange assay. There was a significant increase in sister chromatid exchanges in mouse bone marrow cells at concentrations ≥ 100 ppm and the test was judged to be positive (Cunningham et al, 1986).

A limited number of studies has been conducted in the rat, and 1,3-butadiene has been found to be non-mutagenic in this species. Cunningham et al (1986) exposed male B6C3F1 mice and male Sprague-Dawley rats to 0 or 10 – 10,000 ppm (22-22126 mg/m3)1,3-butadiene for 6 hours/day on two consecutive days. Animals were sacrificed 24 hours after the second exposure and the bone marrow sampled to examine for the presence of micronuclei. A dose-related increase in the incidence of micronuclei was seen at 1,3-butadiene concentrations of 100 ppm and higher in the mouse, but there was no difference in the incidence of micronuclei between control and exposed rats at any concentration. Cunningham et al (1986) conducted a sister chromatid exchange assay in rats. Male Sprague-Dawley rats were exposed to 1,3-butadiene by inhalation, at concentrations from 10 to 10,000 ppm (22-22126 mg/m3), 6h/day, for 2 consecutive days. Bone marrow cells were evaluated for the induction of sister chromatid exchanges. No significant increases in sister chromatid exchanges occurred.

Gene mutation at the hrpt locus has also been investigated in rats. In the study of Meng et al (2007) mutation frequencies in splenic T cells were determined in male rats exposed to 1,3- butadiene at 1250 ppm (2765 mg/m³)(6 h/day, 5 days/week) for 2 weeks and compared to previous results in female rats (Meng et al 1998, 1999, Walker and Meng 2000). 1,3-Butadiene was weakly mutagenic in rats, mutation frequencies in treated male rats were 1.9-fold greater than in control males whilst the figure in female rats was 1.9-fold higher than that in males. Hrpt mutations in female rats were also seen after exposure to the lower dose of 62.5 ppm (138mg/m³)1,3- butadiene for 4 weeks. A small but statistically significant increase in mutation frequency over controls occurred

1,3-butadiene is therefore mutagenic in somatic cells in the mouse but not in the rat in standard cytogenetic and gene mutation studies. A weak positive response was seen for hrpt mutations in the rat.

 

1,3-Butadiene has also been examined for germ cell mutagenicity. Adler et al (1994) reported a dominant lethal assay in which male (102/E1xC3H/E1)F1 mice were exposed to 0 or 1,300 ppm (2876 mg/m3) 1,3-butadiene 6 hours/day for 5 days. Each male was then mated with pairs of unexposed females for a period of 4 consecutive weeks. Pregnant females were sacrificed on days 14-16 of gestation and the uterine contents were examined for the presence of live and dead implants. A positive result for dominant lethal mutations was based on post-implantation losses seen primarily in the second week post-exposure. Male mice were exposed to 1,3-butadiene (12.5 or 125 ppm; 27 or 276 mg/m3) for 10 weeks or for a single 6 h period. 1,3-Butadiene caused a statistically significant increase in dominant lethality at 125 ppm but not 12.5 ppm. No significant increase in testicular DNA repair was found with either dose level or exposure period while only 6 h exposure to 125 ppm caused a small but significant increase in DNA damage as detected by the Comet assay. These effects demonstrate the genotoxicity of 1,3-butadiene to germ cells at 125 ppm (276 mg/m3) in the mouse but do not confirm its ability to cause abnormalities in the offspring via the sperm (Brinkworth et al, 1998).

Pacchierotti et al (1998) however, showed cytotoxic genetic effects in the sperm of male mice exposed to 1,3-butadiene (up to 1300 ppm; 2876 mg/m3) and chromosome-type structural aberrations in first-cleavage embryos conceived by these males (see Section on Toxicity to Reproduction).Other studies have reported positive results for 1,3-butadiene in the dominant lethal assay in the mouse (EU RAR 2002).

The potential for 1,3-butadiene to induce dominant lethal mutations in the rat was investigated by BIBRA (1996). Male Sprague-Dawley rats were exposed to 0, 65, 400 or 1,250 ppm (143, 885 or 2765 mg/m3) 1,3-butadiene for 6 hours/day, 5 days/week for 10 weeks. Each male was then allowed to mate with two untreated females over a 10 day period. Females were sacrificed on day 20 of pregnancy and numbers of corpora lutea, live implantations, early deaths, late deaths and dead fetuses were recorded. 1,3-Butadiene had no effect on the parameters measured.

 

1,3-butadiene is therefore mutagenic in germ cells in the mouse but not in the rat.

 

 

In Vivo Studies – Human information

 

There is a significant body of information from human studies in an occupational setting. Endpoints examined have included both gene mutation and cytogenetic analysis. Studies have been conducted on several groups of 1,3-butadiene-exposed workers, both in 1,3-butadiene monomer production and in the polymerization of 1,3-butadieneby different investigators. Although exposures were low compared to the animal genotoxicity studies, internal exposure and production of the epoxides metabolites were shown to occur based on the results of various biomarkers of exposure. Most of the studies did not show any association between 1,3-butadiene exposure and increased gene mutations, primarily HPRT mutations (Hallberg et al 1997, Zhang et al 2004, Liu et al 2008, Fustinoni et al 2004, Lovreglio et al 2006, Albertini et al, 2001, 2003 & 2007, Wickliffe et al 2009).Although some genotype-associated differences in metabolic patterns were observed (Albertini 2007), these were without differences inHPRTmutations or chromosome aberrations.In earlier studies, one group of investigators, however, did show a relationship in workers exposed to 1,3-butadiene in monomer production and in the styrene-butadiene rubber industry in Texas, USA (Legator et al, 1993, Ward et al, 1994, 1996, 1997 & 2001, Ammenheuser et al 2000 [summarised in EURAR 2002]). A different method was used by these investigators to measure the HPRT mutations than in the other studies, and there are questions on whether co-exposures were adequately accounted for. Nevertheless, a recent study from these investigators, using their same method, have shown that reduced exposures to all potential genotoxic agents in these facilities have resulted in negative findings (Wickliffe et al, 2009). It was initially reported that there was an increase in frequency of chromosome aberrations in a group of 1,3-butadiene-exposed Czech workers (Sram et al, 1998). Subsequent studies which measured DNA adducts in the same blood samples as used for the cytogenetic studies showed no positive relationship between adducts and chromosome changes, although the adducts were good biomarkers of individual exposure (Zhao et al, 2001). This seems to suggest that 1,3-butadiene was not the agent responsible for the cytogenetic findings..

 

 

Conclusions

 

1,3-Butadiene has been examined for mutagenicity both in vitro and in vivo in a range of recognised core assay types. It has shown positive results for mutagenicity in vitro in both bacterial and mammalian cell systems, and in vivo in both somatic cells and germ cells in the mouse. A more limited, but nevertheless adequate evaluation in rat somatic and germ cells using comparable endpoints has given negative results. There is therefore evidence for species differences in regard to the genotoxicity of 1,3-butadiene. It is known to require metabolism in order to produce genotoxic entities, and it is likely that the response of species to the material will in part depend on the nature and extent of metabolism (see Section on Toxicokinetics, Metabolism and Distribution). The available data on several groups of 1,3-butadiene-exposed workers, both in 1,3-butadiene monomer production and in the polymerization of 1,3-butadiene, did not show any association between 1,3-butadiene exposure and increased gene mutations, primarily HPRT mutations. One group of investigators have shown a relationship in workers exposed to 1,3-butadiene but a different method was used by these investigators to measure the HPRT mutation than in the other studies, and there are questions on whether co-exposures were adequately accounted for. Nevertheless, a recent study from these investigators has shown that reduced exposures to all potential genotoxic agents in these facilities have resulted in negative findings.  No 1,3-butadiene-related chromosome aberrations have been demonstrated in humans.

 

It is concluded that the available data indicate that 1,3-butadiene is genotoxic in vitro and in vivo in both somatic and germ cells in the mouse but is not genotoxic in vivo in both somatic and germ cells in the rat. Similar conclusions have been published in the EU RAR (2002) and SCOEL (2007).A weak positive response was seen for hrpt mutations in the rat.

 

 

Additional References

 

EU RAR (2002). European Union Risk Assessment Report for 1,3-butadiene.Vol. 20. European Chemicals Bureau (http://ecb.jrc.ec.europa.eu/DOCUMENTS/Existing-Chemicals/RISK_ASSESSMENT/REPORT/butadienereport019.pdf)

 

SCOEL.(2007). Recommendation from the Scientific Committee on Occupational Exposure Limits: risk assessment for 1,3-butadiene.SCOEL/SUM/75 final (updated Feb 2007).

 

Short description of key information:
Reaction mass of butane and butene containing > 0.1 % butadiene: mutagenic
Reaction mass of butane and butene containing < 0.1 % butadiene: not mutagenic

Endpoint Conclusion:

Justification for classification or non-classification

1,3-butadiene is classiefied in Annex VI of the CLP as Carc. Cat. 1A (formerly R45) and Muta. Cat. 1B (formerly R46). According to the CLP, "Reaction mass of butane and butene" has to be classified as Carc. Cat. 1A (formerly R45) and Muta. Cat. 1B (formerly R46) if the content of 1,3 -butadiene is equal to or above 0.1 %. Testing for genetic toxicity and carcinogenicity is therefore not required in accordance with Column 2 of REACH Annex VII and Annex X.

If the content of 1,3 -butadiene is below 0.1 %, no classification and labeling is required as the available data for the other components (butene, butane, 2 -methylpropene and isobutane) shows that they are not mutagenic.