Fuels, diesel, co-processed with hydrocarbons derived from thermally cracked waste plastics

Carcinogenicity

Description of key information

Seven repeated dose dermal studies in mice were identified for samples of structurally related middle distillate fuels.  Materials were applied either neat or as dilutions in solvent, to the clipped skin of mice two or three times per week for either 2 years or the lifetime of the animal. In these studies there was an increase in skin tumour yield with the majority of samples tested. Numbers of animals showing dermal tumours was relatively small and the tumours had a long latent period. The samples also caused significant non-neoplastic dermal changes including hyperplasia which may have contributed to the tumorigenic response. 
It is concluded that these materials are at best weakly carcinogenic but that the response may have been mediated by a non-genotoxic mechanism, involving repeated skin damage.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: dermal

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

Not reported, but stated to be conducted over a 4 year period

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable with restrictions because the study was well conducted and acceptable, but all pertinent information was not provided and analysis for polycyclic aromatic hydrocarbons may not have been sufficiently sensitive.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Compound was applied dermally 3 times a week for the lifespan of the animal (only male mice used) and animals were examined for dermal tumours. Animals were examined grossly for internal tumours at the end of the study period.

GLP compliance:

not specified

Species:

mouse

Strain:

other: C3H/HeJ

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Jackson Laboratories, Bar Harbor, Maine
- Age at study initiation: 6 to 10 weeks old
- Weight at study initiation: Not reported
- Housing: Five per suspended wire mesh cage
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: Not reported


ENVIRONMENTAL CONDITIONS
- Temperature (°C): Only stated to be according to U.S. Department of Health, Education, and Welfare standards.
- Humidity (%): Only stated to be according to U.S. Department of Health, Education, and Welfare standards.
- Air changes (per hr): Only stated to be according to U.S. Department of Health, Education, and Welfare standards.
- Photoperiod (hrs dark / hrs light): Only stated to be according to U.S. Department of Health, Education, and Welfare standards.


IN-LIFE DATES: Not reported

Route of administration:

dermal

Vehicle:

unchanged (no vehicle)

Details on exposure:

TEST SITE
- Area of exposure: Not reported
- % coverage: Not reported
- Type of wrap if used: None reported
- Time intervals for shavings or clippings: Once a week


REMOVAL OF TEST SUBSTANCE
- Washing (if done): None reported


TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 25 microlitres
- Constant volume or concentration used: yes


USE OF RESTRAINERS FOR PREVENTING INGESTION: no

Analytical verification of doses or concentrations:

no

Details on analytical verification of doses or concentrations:

Not applicable

Duration of treatment / exposure:

Lifetime

Frequency of treatment:

three times a week

Post exposure period:

None

Remarks:

Doses / Concentrations:
25 µL
Basis:
other: amount applied

No. of animals per sex per dose:

Forty to fifty males per treatment group

Control animals:

yes

Details on study design:

- Dose selection rationale: Not reported
- Rationale for animal assignment (if not random): Not reported

Positive control:

Different dilutions of catalytically cracked clarified oil

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: No data


DERMAL IRRITATION (if dermal study): Yes, but details were not provided


BODY WEIGHT: No data


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No


WATER CONSUMPTION: No


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: No


CLINICAL CHEMISTRY: No


URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No


OTHER: Animals were observed daily for the development of skin tumours.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes, skin tumours, skin from the treated area, abnormal tissues, brain, heart, lungs, spleen, kidneys. liver, cervical and mesenteric lymph nodes.

Other examinations:

None reported

Statistics:

Mortality rates were examined using the product limit method and tumour incidence was analysed using Fisher's Exact Test.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY: There are no data on the clinical signs, but there were no effects on the median survival time in any of the treatment groups. However, all dilutions of the positive control significantly reduced the median survival time.


GROSS PATHOLOGY: Only results for gross skin tumours were provided. There was a statistically significant increase in total tumour bearing animals with all compounds except the virgin heating oil blending oil with 59% catalytically cracked middle distillate and the light catalytic cycle oil (100% catalytically cracked). Skin hyperplasia, hyperkeratosis/parakeratosis, dermatitis, epidermal degeneration and necrosis occurred in all groups including the negative control; however, for most of the treatment groups the incidence and/or severity was greater than in the negative controls.


HISTOPATHOLOGY: NEOPLASTIC: There were no increases in internal tumours. The report did not provide a break down of the types of skin tumours, but it was stated that tumours were generally malignant and in some cases metastasized.

Relevance of carcinogenic effects / potential:

Eight of the tested middle distillates demonstrated carcinogenic potential.

Dose descriptor:

other: tumour development

Effect level:

25 other: µL

Sex:

male

Basis for effect level:

other: skin tumour development

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

Treatment with a highly refined oil in the negative control groups produced no tumours, whereas the positive control group treated with catalytically cracked clarified oil at concentrations of 1%, 3.3%, 20% and 25% showed tumour incidences of 18%, 78%, 100% and 98% respectively, with time to first tumour of 61, 37 16 and 17 weeks.

Sample	Median survival (wks)	Total tumour bearing animals	Tumour bearing animals (%)	Time to first tumour	Median time to first tumour
Straight run components
Blending base (Straight run gas oil)	75	7/50	14	58	110
Lightly refined paraffinic oil	84	9/50	18	54	115
No. 2 fuel oil
Sample 3 (CC)	80	6/50	12	94	124
Sample 4 (50% CC)	71	6/40	15	69	113
Sample 5 (37% CC)	85	11/50	22	64	114
Sample 6 (25% CC, 75% Coker liquids)	84	5/50	10	47	127
Sample 7 (20% CC)	85	9/50	18	64	116
Sample 8 (20% CC)	85	10/50	20	51	114
Lab blend (59% CC)	64	1/50	2	113	-
Light catalytic cycle oil (100% CC)	78	2/50	4	90	140

CC= Catalytically Cracked                        Coker liquids=Coker (cracked) gas oil

No indication was given of tumour type or the proportion of benign versus malignant tumours.

Conclusions:

Middle distillates have a weak carcinogenic potential as demonstrated by the low tumour yield and the long latent periods.

Executive summary:

The dermal carcinogenicity of 10 middle distillate samples was tested. Of the 10, 7 samples were described as heating oil no. 2 and therefore covered under CAS 68476 -30 -2. Some individual polycyclic aromatic hydrocarbon (PAH) analysis was provided on selected samples in which very high phenanthrene levels were found in virgin heating oil blending oil with 59% catalytically cracked middle distillate and the light catalytic cycle oil (100% catalytically cracked. A high phenanthrene level was also found in blending base (straight run gas oil). Moderate or high pyrene levels were seen in commercial No. 2 heating oil (50% catalytically cracked) and virgin heating oil blending oil with 59% catalytically cracked middle distillate, respectively. It was stated, however, that these PAHs were all non-carcinogenic. In view of some large sensitivity values (e.g., chrysene <108 ppm), however, it would seem that the analysis method was insufficiently sensitive to measure the critical levels of 4-6 ring PAHs that may have been present in the samples.

Undiluted test material (25 µL) was applied three times weekly to the shorn dorsal skin of groups of 40 or 50 male C3H/HeJ mice for the lifetime of each animal or until all of the animals in the test group developed grossly diagnosed carcinomas. In addition, four groups of 40 or 50 male negative control mice were treated with 25 µL of a highly refined white mineral oil regarded as non-carcinogenic. Also, four positive control groups of 40 or 50 male mice were treated with 1%, 3.3%, 20% or 25% dilutions of a catalytically cracked clarified oil, which has been shown to produce skin tumours in previous studies.

Animals were examined daily for the appearance of tumours which, if present, were examined and grossly classified. A final classification was made after microscopic examination following study termination. At study termination a complete necropsy was carried out and all body cavities were examined. Abnormal tissues were fixed for subsequent histopathological examination. The following tissues were also taken for histopathological examination: skin from treatment site, cutaneous masses, other masses, brain, heart, lungs, spleen, kidneys, liver and lymph nodes. 

Treatment with a highly refined oil in the negative control groups produced no tumours whereas the positive control group treated with catalytically cracked clarified oil at concentrations of 1%, 3.3%, 20% and 25% showed tumour incidences of 18%, 78%, 100% and 98% respectively, with time to first tumour of 61, 37 16 and 17 weeks. There was a statistically significant increase in total tumour bearing animals with all compounds except the virgin heating oil blending oil with 59% catalytically cracked middle distillate and the light catalytic cycle oil (100% catalytically cracked). No indication was given of tumour type or the proportion of benign versus malignant tumours.

Clear evidence of skin irritation/skin injury was seen with all the test materials including hyperplasia, hyperkeratosis, dermatitis, epidermal degeneration and epidermal necrosis.

Tumour incidences in internal organs were reported to be sporadic and, except for hepatocellular carcinoma, to be of low frequency. No treatment related increase in tumours in internal organs was reported.

It was noted by the authors that there was a significant increase in skin tumour yield with the majority of samples tested, but that non-neoplastic dermal changes including hyperplasia may have contributed to the tumourigenic response. In view of the questionable adequacy of the PAH analysis and the high levels of phenanthrene and pyrene found in some samples it is uncertain whether a genotoxic mechanism can be ruled out.

This study received a Klimisch score of 2 and is classified as reliable with restrictions because the study was well conducted and acceptable, but all pertinent information was not provided and analysis for polycyclic aromatic hydrocarbons may not have been sufficiently sensitive.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Study duration:

chronic

Species:

mouse

Justification for classification or non-classification

The dermal carcinogenic potential of representative samples of middle distillate fuels have been investigated in a number of published studies. Materials were applied either neat or as dilutions in solvent, to the clipped skin of mice two or three times per week for either 2 years or the lifetime of the animal. In these studies there was an increase in skin tumour yield with the majority of samples tested. Numbers of animals showing dermal tumours was relatively small and the tumours had a long latent period. The samples also caused significant non-neoplastic dermal changes including hyperplasia which may have contributed to the tumorigenic response. It is concluded that these materials are at best weakly carcinogenic but that the response may have been mediated by a non-genotoxic mechanism, involving repeated skin damage.

Additional information

The dermal carcinogenic potential of representative samples of distillate fuels has been investigated in a number of published studies. Materials were applied either neat or as dilutions in solvent, to the clipped skin of mice two or three times per week for either 2 years or the lifetime of the animal. In these studies there was a significant increase in skin tumour yield with the majority of samples tested. Numbers of animals showing dermal tumours was relatively small and the tumours had a long latent period. The samples also caused significant non-neoplastic dermal changes including hyperplasia which may have contributed to the tumorigenic response. It is concluded that these materials are at best weakly carcinogenic but that the response may have been mediated by a non-genotoxic mechanism, involving repeated skin damage.

Justification for selection of carcinogenicity via dermal route endpoint:
One of seven well conducted mouse skin painting studies

Carcinogenicity: via dermal route (target organ): other: skin