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EC number: 203-438-2
CAS number: 106-88-7
The most critical effect is tumorigenicity. Butylene oxide has caused
nasal and lung tumors in rats (2 years inhalation). This indicates that
Butylene oxide is a potential carcinogen, at least at high
concentrations at the port of entry. Inhalation appears to be the most
important route of exposure and the resultes 2 years inhalation study
(see below) provide a basis for a quantitative estimation of the risk of
exposure. For dermal exposure such data are lacking. On the other hand,
skin exposure does not appear to be a common route of exposure and the
high vapour pressure and volatility of the material and its irritating
properties indicate that dermal exposure will be minimal. Therefore, no
DNELs/DMELs were derived for dermal exposure. Furthermore, no
DNELs/DMELs are proposed for acute exposure for the material is a local
carcinogen at the port of entry and with effects being concentration
dependent and no data are available so far which would definitely
support for acute exposures a clearly higher concentration than the
chronic DMEL. The chronic DMEL is based on the local tumours obtained at
the port of entry. It is further proposed that the DMEL derived for
these local tumours provides also sufficient protection from any
The following tumor incidences were obtained in male rats:
At 400 ppm there was a markedly decreased survival in male rats. In
females, a low tumor response was seen only at 400 ppm. For the nasal
tumors in males a T25 of 413 ppm is obtained. For lung tumors in males a
T25 of 568 ppm (calculated from the top dose) or 562 ppm (calculated
from the lower dose ) is obtained. A linear extrapolation from a T25 of
500 ppm as a point of departure would indicate a numerical risk of
1:2000 at 1 ppm. However, the real risk is assumed to be lower due to a
likelyhood for non-linear elements in the dose response relation at
lower doses (as has been shown for propylene oxide). 1 ppm (= 3 mg/m3)
can therefore serve as a preliminary DMEL for butylene oxide.
No DNEL/DMEL is proposed for the general population, since the material
is not foreseen in consumer products.
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