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EC number: 295-518-9
CAS number: 92062-05-0
A complex combination of hydrocarbons obtained from the vacuum distillation of the products from a thermal cracking process. It consists predominantly of hydrocarbons having carbon numbers predominantly greater than C34 and boiling above approximately 495°C (923°F).
Table 1. Non-neoplastic lesions of the respiratory tract
Nasal and paranasal cavities
Olfactory epithelial basal cell hyperplasia
Respiratory epithelial hyperplasia
Mucous (goblet) cell hyperplasia
Olfactory epithelial eosinophilic cytoplasmic inclusion(s)
Respiratory epithelial eosinophilic cytoplasmic inclusion(s)
Mucosal mononuclear/inflammatory cell infiltration
Bronchiolo-alveolar hyperplasia, bronchiolar type
Mononuclear/inflammatory cell infiltration
Lung associated lymph nodes
Accumulation of foamy macrophages (histiocytosis)
different from the control * p<0.05; ** p<0.01, *** p<0.001
Read across for the key inhalation studies is justified because fumes of
air-rectified bitumen have been shown to be comparable with fumes of
straight-run paving bitumen. In a comparative analytical study, fumes
from a straight-run and an air-rectified bitumen were closely similar in
terms of composition and physical properties.
A two-year bioassay with fumes from a blended paving bitumen
(air-rectified and vacuum residue) was conducted in Wistar rats
(Crl:WI(WU)BR). The animals, 50 males and 50 females per dose group,
were exposed nose-only to fumes regenerated from the bitumen fume
condensate at target concentrations of 0 (clean air) and nominal
concentrations of 4, 20 and 100 mg/m3 total hydrocarbon concentration
for 6 h/day, 5 days/week for 104 weeks. These concentrations were chosen
based on a series of range-finding experiments in which the animals at
the highest dose showed signs of slight respiratory irritation. The mean
actual concentrations in the study, measured as total hydrocarbon (THC,
sum of aerosol and vapour), were 0, 4.1±0.3, 20.7±1.8, and 103.9±9.7
mg/m3 using the methodology described by BIA (Berufsgenossenschaftliches
Institut fuer). (Note: taking into account the conversion factor of 1.66
between the absolute concentration of fumes from bitumen and the
concentration measured with this method, the concentrations were 0, 6.8
mg/m3, 34.4 mg/m3, and 172.5 mg/m3, respectively.) Additional control
animals (36) and animals exposed to the high dose (36) were included in
the study to conduct bronchio-alveolar lavage (BAL) and to investigate
proliferation of respiratory epithelia, at 7 days, 90 days and 12 months
following the start of exposure. In the main study, no statistically
significant differences in mortality incidence were observed among the
various groups: the mortality prior to final sacrifice was 10, 18, 16
and 14% in the males and 28, 12, 16 and 22% in the females for the
control, low, medium and high dose groups, respectively. A statistically
significant reduction of body weight gain was observed in the medium
dose groups from day 119 (males and females) and in the high dose groups
as of day 21 (males) or day 28 (females). The difference at sacrifice
averaged –3% (males) and –8% (females) of the medium dose group and –7%
(males) and –8% (females) in the high dose group.
Lactic dehydrogenase activity in BAL fluid, indicating an increased
permeability of cell membranes, was slightly elevated in the exposed
females (but not males). However, the absolute values were low and below
the values of historical controls and were considered of minor relevance
by the investigators.g-Glutamyltransferase levels in BAL fluid,
indicative of increased phagocytic activity of macrophages, were
slightly increased in both males and females. Overall results of BAL
investigations showed that effects, if any, were very slight to slight.
The authors conclude that the broncheoalveolar region of the respiratory
tract is not significantly impacted by exposure to bitumen fume. Unit
Length Labelling Index was comparable in lung parenchyma of treated and
control animals. No consistent effects on cell proliferation were seen
for level 1 respiratory epithelium, level 1 non-ciliated epithelium and
level 3 olfactory epithelium. The only consistent increase in
proliferation was seen in the transitional zone of respiratory to
olfactory epithelium in the exposed males, but not females. At the
mid-dose level (20.7 mg/m3) the full histopathology at the termination
of the study after 2 years of exposure showed some slight effects in the
nasal passages. In particular hyperplasia of mucous cells (goblet cells)
and eosinophilic cytoplasmic inclusions in the olfactory epithelium was
observed. In addition, a statistically significant increased incidence
of mononuclear cell infiltrates was seen in the epithelium of the nasal
and paranasal cavities in animals of the mid- and high-dose groups.
These effects were also seen at a lower incidence in the animals of the
control and low-dose groups and are probably adaptive in nature.
The NOAEL for systemic effects following inhalation was 103.9
mg/m3(172.5 mg/m3adjusted) based on the absence of any histopathological
changes or alterations in haematology. The LOEC for local effects was
20.7 mg/m³ (34.4 mg/m³ adjusted), based on the effects on the nasal
passages. The NOAEC was set at half the LOAEC, that is 10.4 mg/m³ total
hydrocarbon concentration (17.2 mg/m³ adjusted) based on the minimal
effects and the fact that in the 90-day study and the reproductive
toxicity screening studies NOAECs of 20.1 mg/m³ (30.4 mg/m³ adjusted)
and 30 mg/m3were found, respectively.
This study received a Klimisch score of one and is classified as
reliable without restrictions because it was an acceptable study that
was well documented.
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