Asphalt

Endpoint summary

Description of key information

The following studies were identified: two read-across 28-day dermal studies (OECD 410); a 90-day inhalation study; and a read across chronic inhalation study (OECD 451). In addition a supporting inhalation study is available ( 14 days). In a combined repeat dose / reproductive screening study with oxidized asphalt, no significant effects were observed

For the dermal studies performed on rabbits, the LOAEL topical effects for both samples of vacuum residue was 200 mg/kg/day and the NOAEL for systemic effects was >2000 mg/kg; both endpoints were based on absence of significant histopathological findings. For the 90-day inhalation study the NOAEL was 20.1 mg/m³ (28.2 mg/m³ adjusted) based on local effects in the upper respiratory tract. In  the chronic inhalation study, the NOAEL for systemic effects in the rat following inhalation was >103.9 mg/m3 (172.5 mg/m3 adjusted) based on the absence of any significant histopathological changes or alterations in haematology. The LOEC for local effects was 20.7 mg/m³ (34.4 mg/m³ adjusted), based on irritant effects on the nasal passages.  A conservative estimate of 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 a NOAEC of 20.1 mg/m³ (28.2 mg/m³ adjusted) was found.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

172.5 mg/m³

Study duration:

chronic

Species:

rat

Quality of whole database:

Four good quality studies covering 14-day to two years exposure

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

17.2 mg/m³

Study duration:

chronic

Species:

rat

Quality of whole database:

Four good quality studies covering 14-day to two years exposure

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

2 000 mg/kg bw/day

Study duration:

subacute

Species:

rabbit

Quality of whole database:

Two studies available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

1.9 mg/cm²

Study duration:

subacute

Species:

rabbit

Quality of whole database:

two studies available

Additional information

No repeat-dose oral studies on bitumens have been identified. Two studies involving repeated dermal exposure are available. Read across, repeat dose inhalation studies are available on fumes from air-rectified (partially oxidized) asphalt. In addition a combined repeat dose/reproductive screening study is available with oxidized asphalt.

Read across for the key inhalation studies is justified because fumes of air-rectified asphalt have been shown to be comparable with fumes of paving bitumen. In a comparative analytical study, fumes from a straight-run and air-rectified grades were closely similar in terms of composition and physical properties.

28 -day dermal studies, a 90-day inhalation study (Fraunhofer 2001), and a chronic inhalation study (Fraunhofer, 2006) were identified as key studies. Results of these are presented below.It is important to recognize that toxicity studies involving exposure to fumes represent only the volatile fraction of the whole material.

In two 28 -day dermal studies, petroleum vacuum residues (CAS# 64741-56-6) were tested on rabbits (API, 1983c, d). For both studies, four groups of 5 male and 5 female rabbits were exposed to two different samples of vacuum residue once per day, three days/week for 4 weeks (12 applications in total). Doses applied were 0 (sham-exposed), 200, 1000 or 2000 mg/kg body weight. The neat material was slightly heated just prior to application to decrease its viscosity, put on a 4 x 4 inch patch and subsequently applied to shaved dorsal skin under occlusion. After 6 hours the patch was removed and any remaining test material was wiped off using gauze; however, the test material was not completely removed. Body weight was recorded prior to the first application and from then on weekly. Each day, the treatment site was examined and scored for erythema and oedema (Draize scores). Scoring for erythema proved difficult due to residual material on the skin that prevented observance of the colour of the skin. At the end of the study, all animals were sacrificed for clinical chemistry, haematology and histopathology investigations.

With vacuum residue sample 81-13 (API, 1983d), one male from the high-dose group and one female from the control group died on days 9 and 3, respectively. These early decedents had no antemortem signs and hence deaths were considered non-treatment related. One male from the control group and one female from the intermediate-dose group were found moribund and sacrificed on days 6 and 10, respectively. Both animals showed paralysis of the hind limbs the day prior to the sacrifice. These deaths were also not considered treatment-related, but rather as the result of trauma during dosing and wrapping. Treatment-related findings were flaking skin, wheezing and a decreased food-intake (qualitative observation) resulting in less body weight gain in the exposed groups compared to controls. The lesser body weight gain was statistically significant in the high-dose males as compared to the control group. No treatment-related trends were observed in either clinical chemistry or haematology investigations. No treatment-related effects on reproductive organs were noted. Treatment related effects were observed in the skin of most high-dose males and females with very slight to slight oedema observed after the first treatment and consistent in all animals as of day 16 until the last day (day 28). In the intermediate-dose groups (1000 mg/kg) some animals showed slight oedema until day 10; as of day 11 almost all animals showed very slight to slight oedema until the end of the study. In the low-dose group (200 mg/kg) most males showed slight oedema in the last two weeks and most females in the last week of treatment. Gross pathology findings of reddened or thickened skin, were consistent with the microscopic observations of skin effects: minimal to moderate subacute, acanthotic dermatitis and minimal to moderate hyperkeratosis.

With the other sample of vacuum residue 81 -14 (API, 1983c), one male from the low-dose group and one female from the high-dose group were found dead on days 13 and 5, respectively. These early decedents had no antemortem signs and deaths were not considered treatment related. Treatment-related findings were decreased food-intake (qualitative observation), wheezing, flaking skin and some other skin changes such as wart-like lesions and white discharge at the treated sites. No decrease in body weight gain was found in any of the treated groups as compared to the control group. Neither were there any treatment-related trends observed in clinical chemistry or haematology parameters. No treatment-related effects on reproductive organs were noted. Treatment-related dermal effects were observed in most animals from the high-dose group with very slight to slight oedema observed as of the first treatment and consistently observed in all animals from day 17 until the last day (day 28). In the intermediate-dose groups (1000 mg/kg), 3 of the 5 males and 3 of the 5 females showed slight to moderate oedema as of the first day of treatment and continued until the termination of the study (day 28) for 4 of the 5 males and 1 of the 5 females. In the low-dose group (200 mg/kg), 3 of the 5 males showed very slight oedema on some days whilst all females showed very slight to slight oedema on some days. Again, the gross pathology findings (thickened skin) were consistent with the microscopic observations that showed minimal to moderate subacute, acanthotic dermatitis and minimal to moderate hyperkeratosis which is considered to be adaptive in nature.

The LOAEL for both samples of vacuum residuum of 200 mg/kg/day was based on skin irritation, in the absence of significant histopathological findings. The NOAEL for systemic effects was 1000 mg/kg, based on body weight effects. However, as there were no clinical or histopathological findings, the decreased body weight was considered to be secondary to the reduced food intake and the value of 2000 mg/kg/day was taken forward to calculate the DNEL for dermal systemic effects.

In a 90-day inhalation study, fume from asphalt was tested according to OECD 413 under GLP conditions in male and female Wistar WU rats, strain Crl:(WI)WU BR. The fumes were regenerated from a sample of bitumen tank condensate. Each exposure group comprised 16 male and 16 female rats. The animals were exposed to clean air (control), or to target concentrations of 4 mg/m³ (low dose), 20 mg/m³ (mid dose), and 100 mg/m³ (high dose) total hydrocarbon (THC) of bitumen fumes. The duration of the exposure was 6 hours per day, 5 days per week for 14 weeks (except public holidays). The mean actual concentration (aerosol + vapour phase) measured during the 6 hour exposure period was 3.95 mg/m³ THC for the low dose, 20.12 mg/m³ THC for the mid dose, and 106.55 mg/m³ THC for the high dose group, as analyzed by IR spectroscopy. (Note: taking into account the factor (1.4) between the absolute bitumen fume concentration and the bitumen fume concentration determined using the BIA method the concentrations were 5.5 mg/m³ THC for the low dose, 28.2 mg/m³ THC for the medium dose, and 149.2 mg/m³ THC for the high dose group.)

 

The exposure atmosphere comprised of a particulate / vapour mix ; 24.6 % / 75.4 % (4 mg/m³), 42.9 % / 57.1 % (20 mg/m³), and 68.1 % / 31.9 % (100 mg/m³). Since the fume consists of a mixture of compounds with different vapour pressures (volatile and semi volatile) the relative aerosol content decreases with increasing dilution of the fume as expected. The NMAD as measured with the SMPS - system was 105 nm in the 4 mg/m³, 82 nm in the 20 mg/m³ and 86 nm in the 100 mg/m³ group. However, the difference in median size between the three groups of about 23 nm was considered of limited significance since the deposition probability in the rat lung only changes slightly in this size range.

The exposure was well tolerated by all rats with no signs of test substance related adverse effects. A single animal died on day 6 of the study due to a severe congenital hydronephrosis. No test substance related mortality occurred during the study. After one week of treatment, however, a lower mean body weight gain became apparent in the high-dose males. The difference in body weight increased during the course of the study resulting in a markedly lower mean body weight (- 10%) compared to the controls at the end of the study. Milder effects on body weight gain (- 5%) were noted in all female groups exposed to bitumen fumes. The reduced body weight gained appeared to be due to a reduced food intake, since a statistically significant lower food consumption was noted in the male high dose group, which was correlated to the lower body weight.

 

Several clinical parameters changed in the males from the high-dose group: mild dose-related increases in serum urea and potassium and an increase in calcium were observed. However, almost all individual data were found in the normal range. The effects on electrolytes and urea in males are in agreement with a very slight acidosis and/or effect on the kidney.

 

In the female rats from the high dose group a mild increase in mean cell concentrations as well as in lactate dehydrogenase (LDH) and gamma-glutamyltransferase (GGT) was measured in the broncho-alveolar lavage fluid. No clear-cut dose dependence of mean values gamma-glutamyltransferase was observed. Similar, but statistically not significant, effects were seen in the exposed male rats. However, the recovery period for males upon cessation of exposure was 90 hours whereas the recovery period for the females was 18 hours.

 

Statistically significant incidences of test substance-related histopathological changes were only observed in the nasal and paranasal cavities from rats of the high-dose group. Eosinophilic cytoplasmic inclusions (hyalinosis) were observed exclusively in nasal epithelial cells of 8/10 males and 10/10 females of the high dose groups. Associated with degenerative hyalinosis was focal/multifocal basal cell hyperplasia, which could be observed in the olfactory/respiratory transition areas of 4/10 high-dosed males. Another significant treatment-related change was multifocal mucous (goblet) cell hyperplasia. The incidences were 10/10 males and 9/10 females of the high dose group, and 1/10 males of the clean air control group. Multifocal mucosal inflammatory cell infiltration was a further exposure-related adaptive effect, which could be observed exclusively in 4/10 males and 3/10 females of the bitumen high dose group.

 

Effects on the lungs were investigated by pulmonary labelling studies with BrdU and evaluation of the unit length labelling index (ULLI) of the terminal bronchioles. The BrdU derived parenchymal labelling index showed no statistically significant differences between the control and exposed groups, either in the male or in the female rats. However, the mean parenchymal labelling indices were slightly elevated in the males of the medium and high dose groups as compared to the control and low dose groups. In the females, the mean labelling indices were higher in all exposure groups as compared to the control group. No statistically significant differences were found between the control and exposed groups for ULLI, but pronounced variation of the mean values and high standard deviations were observed in the values for ULLI.

 

In conclusion it can be stated that exposure to fumes from bitumen at 106.6 mg/m³ THC led to a significant reduction in body weight gain in males and to statistically significant incidences of mild test substance-related histopathological changes (hyalinosis, basal cell hyperplasia, mucous cell hyperplasia, inflammatory cell infiltration) in the nasal and paranasal cavities. The NOAEC (no observed adverse effect concentration) was 20.1 mg/m³ THC (28.2 mg/m³ adjusted) in the 90-day study.

In the chronic inhalation study, a two-year bioassay with fume from air-rectified (partially oxidized) asphalt was conducted in Wistar rats (Fuhst et al., 2007; Fraunhofer, 2006). The animals, 50 males and 50 females per dose group, were exposed nose-only to fumes regenerated from the fume condensate at target concentrations of 0 (clean air), 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 Arbeitssicherheit,). (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 para nasal 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 NOAEC for systemic effects following inhalation was 103.9 mg/m³ (172.5 mg/m³ adjusted) 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 irritation effects on the nasal passages.

A conservative estimate of 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 a NOAEC of 20.1 mg/m³ (28.2 mg/m³ adjusted) was found.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:

good well conducted chronic study

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:

Only consistent effect was mild irritation of the upper respiratory tract observed in a number of repeat exposure studies. NOEC estimated based on combination of results from 90 day and 2yr exposure studies

Justification for selection of repeated dose toxicity dermal - systemic effects endpoint:

based on similar results observed in two studies

Justification for selection of repeated dose toxicity dermal - local effects endpoint:

Based on similar irritation effects seen in in two studies

Justification for classification or non-classification

Data from repeated dose dermal and inhalation toxicity studies, showed no significant systemic toxicity. Therefore, bitumen is not classified for repeat dose toxicity under CLP Regulation, (EC)1272/2008 as the criteria for classification are not met.