Gas oils (petroleum), straight-run, high-boiling

Endpoint summary

Description of key information

There are no key repeated dose studies (subacute, subchronic, or chronic) for oral exposure.  Two key repeated dose toxicity studies were identified for dermal exposure, one 28-day study (OECD 410) and one 90-day study (OECD 411).  There was one key read-across 90-day repeated dose toxicity study (OECD 413) for inhalation.
For the read-across 90-day inhalation study, a NOAEC of 0.88 mg/L for local effects on the lung (increased relative wet weight in the absence of histopathological change) was established in rats expose to aerosol.  A NOAEC of greater than or equal to 1.71 mg/L is established for systemic effects, based on no significant findings at this level.
For the 28-day dermal study, a LOAEL of 200 mg/kg/day was established based on local irritation. No NOEL was determined for local irritation.  The NOAEL for systemic effects following repeated dermal exposure was greater than or equal to 2000 mg/kg/day.
For the 90-day dermal study, the LOAEL was 125 mg/kg/day in rats, based on increased liver and spleen weights, altered bone marrow function (decreased haematopoiesis, red blood cell count, haemoglobin, and haematocrit) and liver histopathology. The NOAEL was 30 mg/kg/day. These systemic changes occurred in the absence of any appreciable skin irritation, resulting in a NOAEL for local effects of greater than or equal to 500 mg/kg/day, the highest dose tested.

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

1 710 mg/m³

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

30 mg/kg bw/day

Additional information

There are no key repeated dose studies (subacute, subchronic, or chronic) for oral exposure. For the 28-day dermal study, the skin was the primary site of toxicity for straight run middle distillate with dose-dependent increases in irritation and inflammation apparent both macroscopically and microscopically in rabbits exposed to 200, 1000 or 2000 mg/kg/day. Local irritation was minimal in animals treated with 200 mg/kg body weight/day. Increased granulopoiesis of bone marrow was present in high-dose animals, and was apparently considered by the study authors to be linked to skin damage at the treatment site; however, since lower dose groups were not examined no NOAEL can be established for this finding. Therefore, a LOAEL of 200 mg/kg/day was established based on local irritation. No NOAEL was determined for local irritation. The NOAEL for systemic effects following short-term repeated dermal exposure was greater than or equal to 2000 mg/kg/day. For the 90-day dermal study, the LOAEL was 125 mg/kg/day in rats, based on increased liver and spleen weights, altered bone marrow function (decreased haematopoiesis, red blood cell count, haemoglobin, and haematocrit) and liver histopathology. The NOAEL was 30 mg/kg/day. These systemic changes occurred in the absence of any appreciable skin irritation, resulting in a NOAEL for local effects of at least 500 mg/kg/day, the highest dose tested. For the read-across 90-day inhalation study, a NOAEC of 0.88 mg/L for local effects on the lung (increased relative wet weight in the absence of histopathological change) was established in rats exposed to 0, 250, 750 or 1500 mg/m3 aerosol. A NOAEC of greater than or equal to 1.71 mg/L is established for systemic effects, based on no significant findings at this level.

Inhalation Toxicity

The following study on diesel fuel (Lock, 1984; Klimisch score =2) was included as a source of information for read-across to straight run gas oils.Compositional and physico-chemical data show that VGOs/HGOs/Distillate Fuels are very similar to Straight-Run Gas Oils. It is considered appropriate, therefore, to read across from the VGOs/HGOs/Distillate Fuels data to Straight-Run Gas Oils. 

In a 90-day sub-chronic inhalation toxicity study on diesel fuel (read across from VGO/HGO/Distillate Fuels), groups of male and female Sprague-Dawley rats were exposed whole body to 250, 750 or 1500 mg/m³aerosol (MMAD 0.43-0.75 microns) 4 hour per day, two days per week for 13 weeks (total of 26 exposures) (analytical concentrations:0.35, 0.88, and 1.71 mg/L)(Klimisch score = 2, Lock et al., 1984). There were no deaths during the exposure phase or during the 2-month recovery period. Animals were described as inactive during treatment but no overt clinical signs were present. Body weight was decreased in both the sham control and the diesel-exposed groups relative to animal room controls at the start of exposure (that is, when the animals were first introduced into the chambers). Terminal body weights (after 25 exposures) were significantly decreased in the groups of females, relative to the sham controls. Body weights for exposed males were comparable to the sham control group by the third week of the recovery period, whereas statistically significant decreases remained in mid- and high-dose females until recovery weeks 7 and 5, respectively.

 

Results demonstrate statistically significant alterations in a number of parameters (body weight, food consumption, startle reflex, certain lung function parameters) in rats following sub-chronic inhalation exposure to diesel aerosol, however the magnitude of these changes was small suggesting that they are of doubtful biological relevance. Statistically significant increases in relative liver weight and relative wet lung weight were observed in animals exposed to 1.71 mg/L (analytical concentration) diesel aerosol for 13 weeks, however there was no histopathological involvement, again making the relevance of these findings unclear.  It is noted that the use of whole body exposure probably resulted in ingestion of the test sample during grooming, and may account for the systemic findings that were observed. All of the changes present following 13 weeks exposure were reversed after a 2-month recovery period. A conservative sub-chronic NOAEC of 0.88 mg/mL is determined for local effects on the lung (increased relative wet weight in the absence of histopathological change). A NOAEC of≥1.71 mg/L is established for systemic effects, based on no significant findings at this level.

Dermal Toxicity

Key repeated dose toxicity studies (Klimisch scores=2) were identified for dermal exposure. In a 28-day dermal toxicity study, straight run middle distillate (API 83 -11) was applied to rabbit (5 per sex per dose) skin at doses of 200, 1000 or 2000 mg/kg/day, three times/week for a total of 12 applications (API, 1985b). The sample was applied under occlusion for 24 hours to clipped backs. Each animal was observed twice daily during the treatment period for clinical signs of toxicity. An assessment of dermal reaction to the test material was made daily and body weights were recorded weekly. At the end of the 28-day treatment period all surviving animals were sacrificed and a gross necropsy was performed. Blood samples were collected and analysed for a range of clinical chemistry and haematological parameters. Major organs were weighed, and a range of tissues from control and high-dose animals were subjected to microscopic examination.

 

One low dose male rabbit died on day 12 (death considered incidental). The only reported clinical signs were soiling of the anal area and soft faeces in one low-dose male (days 22 and 23) and thin appearance for one high-dose female (days 12, 13, and 18-20). Animals from the high- dose group failed to gain weight during the study, whereas, mean body weight gains for the low- and mid-dose animals of both sexes were comparable to the controls.

 

Dose-dependent skin irritation developed gradually over the course of the study, with mean irritation scores (Draize scale) of 0.55, 2.2 and 2.95 for the combined low-, mid- and high-dose groups at study termination. Treatment related skin changes were present in all treated rabbits and included erythema and oedema as well as cracked, flaky, and/or leathery appearance of skin at the test site. Haematological parameters were relatively unaffected by treatment and limited to a statistically significant increase in haemoglobin concentration in the 1000 mg/kg body weight/day males only. In the absence of comparable effects in females or in high-dose males, these findings are not regarded as treatment-related. Similarly, an isolated (10%) increase in blood urea nitrogen in the high-dose male group was considered a chance event (all other clinical chemical parameters were comparable to control values). Absolute and relative right kidney weights, and the relative left kidney weight, were decreased (approx 20%) in high-dose males, but in the absence of supporting changes in clinical chemistry or microscopic pathology, these findings are judged not to be treatment related. Other minor organ weight differences were not dose-related and, in the absence of any other related changes, were not attributable to the test substance.

 

Treatment related macroscopic findings in moribund- and terminally sacrificed animals were confined to the treatment site and consisted of dry, scaly, fissured, crusted, and/or thickened skin. Microscopically, slight to moderate proliferative changes were present in treated skin from all high-dose rabbits, with minimal inflammatory changes also present. These were accompanied in four high-dose males and five high-dose females by increased granulopoiesis of the bone marrow (lower dose groups not examined). This is in contrast to the controls in which there were no findings. There were no changes in any other tissues.

 

Based on these findings, the skin was the primary site of effects for straight run middle distillate with dose-dependent increases in irritation and inflammation apparent both macroscopically and microscopically. Local irritation was minimal in animals treated with 200 mg/kg body weight/day. Increased granulopoiesis of bone marrow was present in high-dose animals, and was considered by the study authors to be linked to skin damage at the treatment site; however, since lower dose groups were not examined no NOAEL can be established for this finding. Therefore, a LOAEL of 200 mg/kg/day is established based on local irritation. However, there were no systemic findings that were considered treatment related. Accordingly, the systemic NOAEL is greater than or equal to 2000 mg/kg/day.

 

In a supporting 28 -day dermal toxicity study, gas oil intermediate was applied to the shaved skin of four groups of ten males and ten female Sprague-Dawley rats, at dose levels of 0.01, 0.10, and 0.50 ml/kg and a sham control (API, 1985b; Klimisch score=2). Animals were dosed once a day, 5 times a week for 4 weeks. No animals died or were sacrificed moribund during the observation period. No significant body weight changes were noted between dose groups and sham group. Very slight to slight dermal irritation was noted during the study (dried skin, erythema and/or eschar). Dermal irritation in five animals was the only test article-related finding noted at necropsy. No treatment-related differences were noted between dose groups and sham group. Similarly no significant differences were noted between dose groups and sham group for haematology or clinical chemistry values. Findings indicate that the application of the test article induced mild epidermal irritation and minimal dermal inflammation at the high dose site. The dermal irritation NOAEL, based on very slight to slight irritation, was 0.01 ml/kg and the systemic NOAEL was 0.50 ml/kg, based on the test protocol.

 

In 90 -day dermal toxicity study, heavy atmospheric gas oil was evaluated in a study reported by Mobil (1992) and published by Feuston et al. (1994). The treatment protocol used in the investigation involved application of the sample at doses of 0, 30, 125, or 500 mg/kg body weight/day to clipped dorsal skin of Sprague-Dawley rats (10 per sex per treatment) 5 days a week for 13 weeks. All animals were fitted with 'Elizabethan' collars for the five treatment days each week to prevent ingestion of test material. Residual test sample was wiped from the skin at the end of this period, and the animals remained untreated over the weekend. Body weights were recorded before application of the first dose of test material and weekly thereafter. Daily observations were made for clinical signs of toxicity, and irritation of the treatment site was assessed once each week. Blood (orbital sinus bleed under diethyl ether anaesthesia) was collected from all animals on weeks 5 and 13, and serum analysed for an extensive range of clinical chemical and haematology parameters. Freshly voided urine was collected within one week of blood collection. The animals were killed and subjected to gross necropsy at the end of the 13 week treatment period. All organs were examined for gross abnormalities and select organs were weighed. About 60 tissues from each rat were sampled and preserved in neutral buffered formalin, and around 23 of these (including any gross lesions) from all control and high-dose animals, together with liver, thymus and sternum from the low- and mid-dose groups, were processed and stained (haematoxylin and eosin) for microscopic examination. In addition tissue samples from the right kidney and median lobe of the liver were preserved in formaldehyde-gluteraldehyde. Residual reproductive tissue (not processed for histological evaluation) from control and high-dose males was prepared for spermatid- and spermatozoa counts and morphology.

 

Two treated males became moribund and were sacrificed (one from 500 mg/kg/day dose group, one from 30 mg/kg/day dose group; time of sacrifice not specified). Skin irritation was generally slight in all treated animals, and considered to be due to local abrasion effects from the collars rather than the test sample. Body weight gain was significantly decreased (11%) in males treated with 500 mg/kg/day; however, no significant body weight differences were noted in any other dose group. Whereas no serum chemistry values were affected by exposure to heavy atmospheric gas oil in the 30 mg/kg/day group, a limited number of parameters were significantly altered in the 125 and 500 mg/kg/day groups. The changes that were considered treatment related included serum urea nitrogen (increased 27% in mid-dose females and 31-35% high-dose animals of both sexes) and sorbitol dehydrogenase (increased 68% in mid-dose females and 106-124% in high-dose animals of both sexes) and serum cholesterol (increased 39% or 117% in mid- or high-dose females only).

 

Red cell counts, haemoglobin concentration and haematocrit were significantly decreased by 8-9% in mid-dose males, by 30-31% in high-dose males, and by 11-13% in high-dose females. Platelet counts were reduced by 23-48% in high-dose animals (greater effect in males). Urinalysis and sperm evaluations showed no treatment-related effects. Macroscopic changes considered related to treatment related included increased liver size, decreased thymus size, thickening of the limiting ridge between the non-glandular and glandular sections of the stomach, and enlarged and reddened lymph nodes.

 

Absolute liver weights were statistically significantly increased by 32-50% in high-dose males and females respectively, with smaller (approx. 15%), non-significant increases in mid-dose animals. Absolute thymus weights were decreased in a dose-related manner in males (reduced by 10%, 19% or 61% for low-, mid- and high dose groups, respectively) and females (9%, 24% or 41% reduction, respectively), an effect that attained statistical significance in both sexes treated with heavy atmospheric gas oil at 500 mg/kg/day. Absolute spleen weights were consistently increased by approx. 10-18% in all treatment groups, but this was only statistically significant for high dose females (18% increase). Absolute heart weight was significantly increased (11%) in high-dose females, and absolute prostate weight significantly decreased (22%) in high-dose males; however, no dose-response relationship was apparent for either tissue. Relative liver weights were statistically significantly increased in mid- (16-21%) and high- (49-56%) dose animals of both sexes, while relative thymus weights were decreased in low-dose males (20% reduction), mid-dose males and females (15-23% reduction) and high-dose animals of both sexes (39-56% reduction, statistically significant). Relative spleen weight increased in a dose-related manner in males (13%, 18%, 25%, respectively) and females (11%, 17%, 22%, respectively), with the changes in the mid- and high-dose groups statistically significant for both sexes. Increases in relative kidney weight (+11%, high-dose females) and relative adrenal (+30%, high-dose males) weights were inconsistently expressed among the sexes and appeared unrelated to dose.

 

Microscopic evaluation revealed a severe reduction in haematopoiesis in sternal bone marrow from rats treated at 500 mg/kg body weight/day; males (10/10) were more susceptible to this effect than females (2/10). The increase in absolute and relative liver weight of treated high-dose rats appeared related to liver hypertrophy (large cells towards the periphery of the lobule in 8/10 males and 10/10 females), focal necrosis (3/10 males, 2/10 females) and connective tissue formation (2/10 males and 1/10 females). Other histopathological changes found in the liver included increased areas of haematopoiesis at>125 mg/kg (affecting 6-8 mid-dose animals and 8-9 high dose animals of both sexes) and a dose-related increase in individual cell death in males (affecting 0/10, 2/9, 5/10 and 7/10 animals from the control, low-, mid- and high dose groups, respectively) but only sporadic changes in females (0/10, 2/10, 2/10, 0/10). Heavy atmospheric gas oil at a dose of 500 mg/kg body weight/day also reduced the number of lymphocytes in the thymus (10/10 males, 8/10 females), but did not appear to affect the levels of circulating lymphocytes. Microscopic evaluation did not reveal any treatment related changes in the spleen, kidney, stomach, lymph nodes or skin.

 

The LOAEL was 125 mg/kg/day, based on increased liver and spleen weights, altered bone marrow function (decreased haematopoiesis, red blood cell count, haemoglobin, and haematocrit) and liver histopathology. The NOAEL was 30 mg/kg/day. These systemic changes occurred in the absence of any appreciable skin irritation, resulting in a NOAEL for local effects of greater than or equal to 500 mg/kg/day, the highest dose tested.

 

Repeated dose toxicity: dermal - systemic effects (target organ) cardiovascular / hematological: bone marrow; digestive: liver; other: skin

Justification for classification or non-classification

Results from dermal exposure indicate irritation at the application site in addition to systemic effects observed in rats at 125 mg/kg bw/day. Straight run gas oils meet the criteria for classification for Specific Target Organ Toxicity (repeated exposure) Category 2 (H373) under the EU CLP Regulation (EC No. 1272/2008).