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EC number: 203-438-2
CAS number: 106-88-7
The test substance is classified according to Annex I of the Directive
67/548/EEC with Carc. Cat. 3, R 40.
NTP (1988) reported a toxicity and carcinogenity study using male and
female rats. Vapour concentrations (whole body exposure) used were 200
and 400 ppm. The study duration was 103 weeks; the frequency of
treatment was 6 hours per day and 5 days per week. With respect to the
benign nasal tumours observed in this study, these showed no sign of
progression to malignancy and must be seen against the background of
extensive non-neoplastic lesions at this dose level (400 ppm). These
tumours are likely to be a direct consequence of the irritant properties
of 1,2-epoxybutane leading to stimulation of cell proliferation. It is,
therefore, highly unlikely that these tumours occur at dose levels which
do not produce chronic tissue irritation. A small but statistically
significant incidence of lung tumours (carcinomas and adenomas combined)
was confined to the male rat and to the top dose level of 400 ppm. These
tumours occurred late in the study and showed no evidence of metastasis.
The increase in malignant lung tumours alone was not statistically
significant. It required the combination of benign and malignant tumours
to obtain the statistical significance to enable NTP to classify
1,2-epoxybutane as "clear evidence of carcinogenic activity".
Furthermore, one could question whether a practical maximum Tolerated
Dose was exceeded in the NTP study in view of the significant upper
respiratory tract irritation. NTP categorized the results obtained with
female rats as "equivocal evidence of carcinogenic activity",
demonstrated by studies that are interpreted as showing a marginal
increase of neoplasms that may be chemically related. Two high dose (400
ppm) females developed benign nasal cavity tumours and 1 female
developed a benign alveolar/bronchiolar tumour. on the other hand, one
female control developed a malignant alveolar/bronciolar tumour. On this
basis it is highly questionable as to whether or not the treated females
could be considered to "show a marginal increase of neoplasms that may
be chemically related".
Male and female mice did not show tumours in any organ at either dose
level in a 102-week inhalation vapour study (whole body). Concentrations
used were 50 and 100 ppm; study duration: 102 weeks; frequency of
treatment: 6 hours per day, 5 days per week (NTP, 1988).
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