Ethylene

Carcinogenicity

Description of key information

There is no evidence of carcinogenicity of ethylene following evaluation in a 2 year rat study.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not specified

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Animal experimental study which predates implementation of GLP and development of study guidelines. Published in peer reviewed literature, limitations in reporting but otherwise adequate for assessment.

Justification for type of information:

N/A

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Principles of method if other than guideline:

N/A

GLP compliance:

no

Remarks:

Study initiated in 1977 and completed 1980. A third party quality assurance audit of the report was completed by Tracor Jitco, Inc, Rockville, Maryland 20852, USA

Specific details on test material used for the study:

not specified

Species:

rat

Strain:

Fischer 344

Details on species / strain selection:

not specified

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS: Fischer-344 rats [CDF (F-344)/CrlBr]
- Source: Charles River Breeding Labs, Wilmington, Mass., USA
- Age at study initiation: approximately 6-7 weeks
- Housing: individually in stainless steel open-mesh cages (6 x 7.5 x 7.5 inch) in a single layer midlevel in each inhalation chamber
- Diet: Wayne Lab Blox (Allied Mills, Chicago, Ill., USA) ad libitum except during exposure
- Water: tap water ad libitum
- Acclimation period: 10 days

ENVIRONMENTAL CONDITIONS IN INHALATION CHAMBERS
- Temperature: 22°C
- Humidity: 50%
- Air changes: approx 15/hr

Route of administration:

inhalation: gas

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Four 8 m3 glass and stainless-steel chambers
- Chambers were supplied with absolute and charcoal filtered air separate from the room air supply
- Ethylene chambers were maintained at slight subatmospheric pressure (0.1-0.5 in. H2O) to avoid any escape of the gas
- The control chamber was under slight positive pressure (0.1-0.5 in. H2O) to minimize any possibility of ethylene entering
- Air flow rate: approximately 15 air changes per hour
- Temperature, humidity, pressure in air chamber: 22°C and 50%. Ethylene gas was metered via heated pressure regulators and precision rotameters into the air supply duct of each test chamber.

TEST ATMOSPHERE
- Brief description of analytical method used: infrared spectrophotometry
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of ethylene in each chamber was sampled every 24 min. with a Miran 1A infrared spectrophotometer. The analytical concentration during each exposure was interpolated from the standard curve. After 526 exposure periods the time weighted average concentrations of ethylene were 0, 301, 1003 and 3003 ppm.

Duration of treatment / exposure:

106 weeks

Frequency of treatment:

6 hours/day, 5 days/week

Post exposure period:

None

Dose / conc.:

300 ppm (nominal)

Remarks:

301 ppm (calculated time weighted average concentration)

Dose / conc.:

1 000 ppm (nominal)

Remarks:

1003 ppm (calculated time weighted average concentration)

Dose / conc.:

3 000 ppm (nominal)

Remarks:

3003 ppm (calculated time weighted average concentration)

No. of animals per sex per dose:

120

Control animals:

other: yes, air exposed

Details on study design:

not specified

Positive control:

N/A

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least once/day

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Every 2 weeks

BODY WEIGHT: Yes
- Time schedule for examinations: Weekly for 1st 6 months, every 2 weeks thereafter

FOOD CONSUMPTION: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: prior to sacrifice
- Dose groups that were examined: All

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 6, 12, 18 and 24 months
- Anaesthetic used for blood collection: No data
- Animals fasted: Yes
- How many animals: 5/sex/group at 6 and 12 months, 10/sex/group at 18 and 24 months.
- Parameters examined: Haemoglobin, haematocrit, total erythrocyte count, total and differential leukocyte counts, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 6, 12, 18 and 24 months
- Anaesthetic used for blood collection: No data
- Animals fasted: Yes
- How many animals: 5/sex/group at 6 and 12 months, 10/sex/group at 18 and 24 months.
- Parameters examined: Serum urea nitrogen, serum glutamic-pyruvic transaminase (alanine aminotransferase), and serum alkaline phosphatase.

URINALYSIS: Yes
- Time schedule for collection of urine: 6, 12, 18 and 24 months
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Parameters examined: Appearance, specific gravity, protein, albumin, pH, ketones, glucose and microscopic appearance.

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

TIME OF SCHEDULED TERMINATION: 5/sex/group from each group at 6 and 12 months, 20/sex/group at 18 months, and 63 to 80 animals/sex/group at 106 weeks were killed using carbon dioxide and necropsied. All unscheduled deaths were necropsied as soon as they were found.

GROSS PATHOLOGY: Yes

ORGAN WEIGHTS: Yes. Brain, heart, kidneys, liver, lungs, and gonads.

HISTOPATHOLOGY: Yes. The following tissues were collected and fixed in 10% neutral buffered Formalin: adipose tissue, adrenal glands, aorta, bladder, bone marrow, brain, ear canal, heart, kidneys, large intestine, liver, lumbar, sacral, and dorsal autonomic ganglia, lungs, lymph nodes, mammary gland, nasal turbinates, oesophagus, ovaries, oviducts, pancreas, parathyroid glands, peripheral nerve, pituitary gland, prostate, proximal and distal portions of the hind limb, salivary gland, skeletal muscle, skin, small intestine, spinal cord, spleen, stomach, thymus, tibial and plantar nerves, trachea, and uterus. Eyes and testes were examined and then fixed in Bouin's solution. All fixed tissues from the high dose and control animals were examined histopathologically.

Other examinations:

N/A

Statistics:

Analysis of variance (Kruskal-Wallis test for ratios) was used to test absolute body weight, total body weight change, organ weights, organ weight/body weight and organ weight/brain weight ratios. Where appropriate, follow-up analysis was performed using multiple comparison techniques including Tukey's for equal-sized groups and Scheffe's for groups of unequal sizes. Haematology data were tested for homogeneity of variance, transformed as needed, and analyzed by analysis of variance.

Clinical signs:

no effects observed

Description (incidence and severity):

N/A

Dermal irritation (if dermal study):

not examined

Description (incidence and severity):

N/A

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Of the 960 animals used for the study, 151 unscheduled deaths occurred and were distributed evenly throughout the groups. At study termination there were 71 males and 74 females, 68 males and 73 females; 64 males and 80 females and 63 males and 75 females for the 0, 300, 1000 and 3000 ppm groups respectively.

Body weight and weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

The mean body weight for male and female rats exposed to 300 ppm and 3000 ppm for 24 months was significantly increased (p<0.05) as compared to controls; however, this was considered not to be treatment-related.

Food consumption and compound intake (if feeding study):

not examined

Description (incidence and severity):

N/A

Food efficiency:

not examined

Description (incidence and severity):

N/A

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

not examined

Description (incidence and severity):

N/A

Ophthalmological findings:

no effects observed

Description (incidence and severity):

N/A

Haematological findings:

no effects observed

Description (incidence and severity):

N/A

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

N/A

Endocrine findings:

not examined

Description (incidence and severity):

N/A

Urinalysis findings:

no effects observed

Description (incidence and severity):

N/A

Behaviour (functional findings):

not examined

Description (incidence and severity):

N/A

Immunological findings:

not examined

Description (incidence and severity):

N/A

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

N/A

Gross pathological findings:

no effects observed

Description (incidence and severity):

N/A

Neuropathological findings:

not examined

Description (incidence and severity):

N/A

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

A variety of proliferative, degenerative and inflammatory lesions were observed but occurred with approximately equal frequencies in the control and ethylene-exposed groups and were typical for the F344 rat.

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

N/A

Other effects:

not examined

Description (incidence and severity):

N/A

Details on results:

N/A

Relevance of carcinogenic effects / potential:

No evidence of carcinogenicity.

Key result

Dose descriptor:

NOAEC

Effect level:

3 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no clinical or histopathological effects

Remarks on result:

other:

Remarks:

3445 mg/m3 air (analytical)

Of the 960 animals used for the study, 151 unscheduled deaths occurred and were distributed evenly throughout the groups. At study termination there were 71 males and 74 females, 68 males and 73 females; 64 males and 80 females and 63 males and 75 females for the 0, 300, 1000 and 3000 ppm groups respectively.

No treatment-related clinical observations were seen. There was no ethylene-induced effect on body weights, organ weights, organ to body weight ratios, or organ to brain weight ratios. The mean body weight for male and female rats exposed to 300 ppm and 3000 ppm for 24 months was significantly increased (p<0.05) as compared to controls; however, this was considered not to be treatment-related. A variety of proliferative, degenerative and inflammatory lesions were observed but occurred with approximately equal frequencies in the control and ethylene-exposed groups and were typical for the F344 rat. Haematology, blood chemistries and urinalysis were all similar to control. There were no statistically significant increases in overall or individual tumour incidences in treated animals relative to controls.

 

Conclusions:

There was no evidence of carcinogenicity in male and female F344/N rats exposed to ethylene by inhalation at concentrations of 0, 301, 1003 and 3003 ppm for 103 weeks. The NOAEC for carcinogenicity was 3003 ppm (equivalent to 3445 mg/m3).

Executive summary:

Groups of 120/sex Fischer 344 rats were exposed to 0, 300, 1000, or 3000 ppm ethylene, 6 h/day, 5 days/week for up to 24 months (average calculated time-weighted concentrations 0, 301, 1003, and 3003 ppm, respectively). Ophthalmology, haematology and clinical chemistry (blood and urine) assessments were made. After 6, 12, and 18 months groups of animals were killed and examined. A complete selection of tissues and organs from all animals in the control and 3000 ppm groups were examined for microscopic lesions.

 

There were 151 unscheduled deaths (15.7% of animals) but no evidence of a treatment-related effect on mortality. There were no gross lesions that were considered treatment-related and histopathological examination revealed a variety of lesions in both the control and 30000 ppm groups, but they were considered typical of those seen in this strain of animal and not related to ethylene exposure. The results provide no evidence that chronic exposure to ethylene at these concentrations, up to 3000 ppm, causes chronic toxicity or is oncogenic in Fischer-344 rats.

The results provide no evidence that repeated exposure to ethylene at these concentrations causes chronic toxicity or is oncogenic in Fischer-344 rats. NOAEC = 3003 ppm (equivalent to 3445 mg/m3).

This was a non-GLP study which predated implementation of study guidelines but it was regularly monitored by independent scientists and the results were subsequently published in peer reviewed literature. Concerns were expressed in the Agrochemical Draft Assessment Report (DAR) in 2008 (fourth stage review under Council Directive 91/414/EEC) specifically over the interpretation of the findings in the study pertaining to mononuclear cell leukaemia (MCL; not detailed in the publication). Subsequent to the publication, the incidence of MCL was discussed in a personal communication to the ACGIH (Swenberg J, Personal Communication July 28 2003). The author recognised the incidence of MCL in males in this study rose from 14% to 22% at the high dose (3000ppm), while in females the respective percentages were 9% (control) and 12% (3000 ppm). However historical data on MCL in inhalation studies suggests the average incidence for MCL in males for the same period was 57% (with a range of 34-70%), while for females was 37% with a range of 24-54%). The author reports that MCL was not significantly increased in this study and that the control groups were unusually low. The personal communication also details re-analysis of the lung pathology slides; this reanalysis confirmed the lung tumours were of spontaneous origin.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

3 445 mg/m³

Study duration:

chronic

Species:

rat

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

There is no evidence that ethylene is carcinogenic. Ethylene does not warrant classification for carcinogenicity under CLP.

Additional information

Human information

There is no information indicating any carcinogenic effects of ethylene. 

 

Non Human information

Carcinogenicity data

The toxicity and oncogenicity of inhaled ethylene was determined in Fischer-344 rats. Groups of 120 of each sex were exposed 6 hr/day, 5 days/week, for up to 24 months to concentrations of 0, 300, 1000 or 3000 ppm ethylene. The calculated time-weighted average concentrations for the 24 months of exposure were 0, 301, 1003, and 3003 ppm, respectively. Animals were investigated for ophthalmological or haematological effects and for clinical chemistry effects on blood and urine. After 6, 12, and 18 months, groups of animals were necropsied and examined. A complete selection of tissues and organs from all animals in the control and 3000 ppm groups were examined for microscopic lesions.

There were 151 unscheduled deaths (15.7% of 960 animals). There was no difference in mortality across groups during the 2-year study. Gross examination of rats dying during the study and those killed as scheduled, did not reveal any lesions attributable to ethylene exposure. Histopathologically, whilst a variety of lesions were observed in both the control and 3000-ppm groups, they were considered typical of those seen in this strain of animal and not related to ethylene exposure.

Overall there was no evidence that repeated exposure to ethylene at concentrations up to 3000 ppm caused chronic toxicity or was carcinogenic in Fischer-344 rats. The NOAEC is 3000 ppm (equivalent to 3445 mg/m3).

Additional supporting recent data for low potential for carcinogenicity

Ethylene has been examined for mutagenicity both in vitro and in vivo in a range of recognised core assay types. It has shown negative results for mutagenicity both in vitro and in vivo. It is concluded that the available data indicate that ethylene has no significant genotoxicity. In a 4-week inhalation study in rats and mice with evaluation of Hprt mutations and micronucleus formation there were no elevations in either Hprt mutations or micronucleus in either species up to 3000 ppm ethylene (Vergnes et al 1994; Walker et al 2000). Other micronucleus studies conducted in rats at 300, 1000, 3000 and 10,000 ppm after 5 days and 90 days of exposure, evaluating both bone marrow and peripheral blood, and using the sensitive flow cytometry technique showed no elevation in micronucleus formation (Dow, 2010).

In the two-year carcinogenicity study, there was no treatment-related increase in the incidence of tumours of rats exposed up to 3,000 ppm ethylene (Hamm et al., 1984). The lack of micronucleus formation in rats exposed to up to 10,000 ppm for 90 days supports the conclusion from the two-year study that ethylene is not carcinogenic to rats.