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EC number: 295-405-4
CAS number: 92045-23-3
A complex combination of hydrocarbons produced by the distillation of the products of a steam cracking process. It consists predominantly of hydrocarbons having a carbon number of C4, predominantly 1-butene and 2-butene, containing also butane and isobutene and boiling in the range of approximately minus 12°C to 5°C (10.4°F to 41°F).
There are no specific studies on the streams in the C4 low 1,3-butadiene category (CAS Numbers; 91052-98-1, 92045-23-3, 95465-89-7, 95465-90-0 and 95465-91-1) but data on one of the component substances (2-methylpropene) indicate that members of this category have low potential for human carcinogenicity. Carcinogenicity studies carried out on 2-methylpropene in rats and mice were reported to produce an increase in thyroid follicular cell tumours. The thyroid tumours occurred only in male rats at the highest exposure concentration (8000 ppm: 18,359 mg/m3) at an incidence slightly above the laboratory historical incidence in control animals and no tumours were observed in female rats or male and female mice. As all component substances in this category are not genotoxic, if 2-methylpropene did cause an increase in thyroid tumors in male rats, a threshold mechanism is likely to be involved and the relevance of tumours of this type to human health is low.
are sufficient data available on component substances to conclude that
streams within the
C4 low 1,3-butadiene category have a low potential for human
carcinogenicity and therefore do not warrant classification under Dir 1999/45/EC
or GHS/CLP. The mammalian toxicity effects of this category will be not
driven by the content of 1,3-butadiene as this is less than 0.1% w/w for
all category members and therefore exempt from classification/hazard
assessment based on this substance.
are no carcinogenicity data on the streams in the C4 low 1,3-butadiene
category (CAS Numbers; 91052-98-1, 92045-23-3, 95465-89-7, 95465-90-0
but data are available on one of the component substances;
2-methylpropene (butene isomer). There are no data available on the
other component substances (butane or isobutane). The members of this
category are not mutagenic (see Section on Mutagenicity) and the
carcinogenic potential of the component substances is low. Based on the
data available, the members of this category have low potential for
human carcinogenicity and therefore do notwarrant
Dir 1999/45/EC or GHS/CLP.
data are as follows:
isomers (butenes): Carcinogenicity studies via inhalation exposure are
available for 2-methylpropene. F344 Rats and B6C3F1 mice were exposed by
inhalation at 0, 500, 2,000 or 8,000 ppm (1147, 4589, 18,359 mg/m3), for
105 weeks (NTP 1998).
incidence of thyroid gland follicular cell carcinoma in male rats
exposed to 8000 ppm was increased compared to the chamber control group
(1/48, 0/48, 0/48, 5/50 at 0, 500, 2000 and 8000 ppm respectively) and
exceeded the historical control range. The NTP therefore concluded that
there was some evidence of carcinogenic activity of 2-methylpropene in
male rats and established a NOAEC of 2000 ppm (4589 mg/m3) for
carcinogenicity in male rats based on the thyroid follicular cell
carcinomas. The relevance of the thyroid follicular tumours for human
cancer risk is questionable as the tumours occurred in male rats only
and not in either sex in mice. There were no precursor lesions, no
dose-response relationship, the tumours were singular and unilateral,
did not form metastases and there was no increase in liver weight
indicating a secondary mechanism. In addition, the thyroid was not a
target organ in repeat dose studies in rats. Although the 10% incidence
of tumours was outside the historical control at the time, reported to
be 0-4% (NTP 1998, Haseman et al 1998), a carcinogenicity study on
propylene (NTP 1985) had a 7% incidence of thyroid follicular carcinomas
in the control group, further diminishing the significance of the
incidence with 2-methylpropene and suggesting that the tumor findings
may have been spurious. IARC (1999) published guidance noting that no
non-radioactive chemical exposure is known to cause thyroid follicular
carcinomas in humans. It concluded that agents causing thyroid neoplasms
in rodents by hormonal imbalance must be non-genotoxic. Although studies
investigating hormonal imbalance have not been conducted,
2-methylpropene is not genotoxic, indicating if 2-methylpropene did
cause an increase in thyroid tumors in male rats, that a non-genotoxic
mechanism, likely to have a threshold, is involved and the relevance of
tumours of this type to human health is low.
is no data on the carcinogenicity of the component substances in humans.Toxicokinetic
data on members of the butenes category (see Toxicokinetics Section),
indicate that humans have the lowest capacity for oxidative metabolism
and the highest for detoxification pathways.
JK, Hailey JR, Morris and RW (1998). Spontaneous neoplasm incidences in
Fischer 344 rats and B6C3F1 mice in two-year carcinogenicity studies: a
National Toxicology Program update. Toxicol Pathol, 26, 428-441
(1985). NTP Toxicology and Carcinogenesis Studies of Propylene (CAS No.
115-07-1) in F344/N Rats and B6C3F1 Mice (Inhalation Studies). Natl
Toxicol Program Tech Rep Ser, 272,:1-146
Sci Publ. (1999). Agents that induce epithelial neoplasms of the urinary
bladder, renal cortex and thyroid follicular lining in experimental
animals and humans: summary of data from IARC monographs volumes 1-69.;
Ed Wilbourn JD, Partensky C, Rice JM. 147,191-209.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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