Isobutyraldehyde

Carcinogenicity

Description of key information

No neoplastic effects were observed in rats and mice after inhalation exposure to up to 2000ppm (NTP, 1999, similar to OECD 451).

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

Reference 1

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

GLP compliance:

yes

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Northwest Laboratories (Richland, WA)
- Age at study initiation: approximately 6 weeks old
- Weight at study initiation: mean males: ca. 126 g and females 102 g
- Housing: housed individually in Stainless steel (Hazleton Systems, Inc., Aberdeen, MD).
- Diet: NIH-07 Open Formula pellet diet (Zeigler Brothers, Inc Gardners, PA); available ad libitum, except during exposure periods changed daily
- Water: Tap water (Rockville municipal supply) via automatic watering system (Edstrom Industries, Waterford, WI); available ad libitum
- Acclimation period: 13/14 days

ENVIRONMENTAL CONDITIONS
- Temperature: 23.8 - 24.2 °C
- Humidity: 52 - 58 %
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
The study laboratory designed the stainless-steel chambers used for the 2-year studies so that uniform vapor concentrations could be maintained throughout the chamber when catch pans were in position. The total volume for each chamber was 2.3 m3 ; the active mixing volume of each chamber was 1.7 m3 . A small particle detector (Type CN, Gardner Associates, Schenectady, NY) was used with and without animals in the exposure chambers to ensure that isobutyraldehyde vapor, and not aerosol, was produced. No particle counts above the minimum resolvable level (approximately 200 particles/cm ) were detected.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

TEST ATMOSPHERE
Chamber concentrations of isobutyraldehyde in the 2-year study were monitored with an on-line gas chromatograph (Hewlett-Packard Model 5840, Palo Alto, CA). Samples were drawn and analyzed from each exposure chamber four times per hour using an 8-port stream-select valve.

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

6 hours per day, 5 days per week

Remarks:

Doses / Concentrations:
500, 1000, or 2000 ppm (ca. 1.5, 2.9, 5.9 mg/L)
Basis:
other: target conc.

No. of animals per sex per dose:

50

Control animals:

yes

Details on study design:

- Dose selection rationale: Based on mortality and increased incidences and severity of nasal lesions observed in the 4000 and 8000 ppm groups in the 13-week study, exposure concentrations selected for the 2-year inhalation study in mice were 500, 1000, and 2000 ppm.

Observations and examinations performed and frequency:

CLINICAL OBSERVATIONS
Clinical findings were recorded at 4 – weeks intervals in the 2-year study until week 91 and every two weeks thereafter.

BODY WEIGHT
Animals were weighed initially, weekly for 12 weeks , monthly thereafter until week 91 , every 2 weeks until study termination, and at the end of the studies.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Necropsy was performed on all animals.

HISTOPATHOLOGY: Yes
Complete histopathology was performed on all rats. In addition to gross lesions and tissue masses, the following tissues were examined: adrenal gland, bone with marrow, brain, clitoral gland, esophagus, heart, large intestine (cecum,colon, and rectum), small intestine (duodenum, jejunum, and ileum), kidney, larynx, liver, lung (and mainstem bronchi), lymph nodes (mandibular and mesenteric), mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, skin, spleen, stomach (forestomach and glandular), testis (with epididymis and seminal vesicle), thymus, thyroid gland, trachea, urinary bladder, and uterus.

Statistics:

The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958). The primary statistical method used for the evaluation of tumor incidence was logistic regression analysis (Dinse and Lagakos, 1983; Dinse and Haseman, 1986; McKnight and Crowley. 1984). Additional methods used included the life table test (Cox, 1972; Tarone, 1975), appropriate for rapidly lethal neoplasms and the Fisher exact test and the Cochran-Armitage trend test (Arrnitage, 1971; Gart er al.. 1979). Tests of significance included pairwise comparisons of each exposed group with controls and a test for an overall dose-related trend.

Clinical signs:

no effects observed

Mortality:

mortality observed, non-treatment-related

Description (incidence):

There was an exposure-related decrease in survival of male mice, and the survival of males exposed to 2,000 ppm was marginally lower than that of the chamber controls, but equal to the mean survival rate of the last 20 inhalation studies. The opposite trend was observed for females. Differences are believed to be due to a rather high survival rate in male control mice and a comparable low survival rate in female control mice compared to historical control data and not treatment related.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

The mean body weights of female mice exposed to 1,000 or 2,000 ppm were lower than those of the chamber controls during the second year of the study. Differences were not significant and all values were within the historical control range.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Nonneoplastic lesions related to test substance exposure were limited to the nose. The incidences of olfactory epithelial degeneration in 1,000 and 2,000 ppm males and females were significantly greater than in the chamber controls.

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

No neoplasms that could be attributed to exposure to the test substance were observed in mice.

Dose descriptor:

NOAEC

Effect level:

>= 5.9 mg/L air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No neoplastic effects observed

Reference 2

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

GLP compliance:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Northwest Laboratories (Richland, WA)
- Age at study initiation: approximately 6 weeks old
- Weight at study initiation: mean males: ca. 126 g and females 102 g
- Housing: housed individually in Stainless steel (Hazleton Systems, Inc., Aberdeen, MD).
- Diet: NIH-07 Open Formula pellet diet (Zeigler Brothers, Inc Gardners, PA); available ad libitum, except during exposure periods changed daily
- Water: Tap water (Rockville municipal supply) via automatic watering system (Edstrom Industries, Waterford, WI); available ad libitum
- Acclimation period: 13/14 days

ENVIRONMENTAL CONDITIONS
- Temperature: 23.8 - 24.2 °C
- Humidity: 52 - 58 %
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
The study laboratory designed the stainless-steel chambers used for the 2-year studies so that uniform vapor concentrations could be maintained throughout the chamber when catch pans were in position. The total volume for each chamber was 2.3 m3 ; the active mixing volume of each chamber was 1.7 m3 . A small particle detector (Type CN, Gardner Associates, Schenectady, NY) was used with and without animals in the exposure chambers to ensure that isobutyraldehyde vapor, and not aerosol, was produced. No particle counts above the minimum resolvable level (approximately 200 particles/cm ) were detected.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

TEST ATMOSPHERE
Chamber concentrations of isobutyraldehyde in the 2-year study were monitored with an on-line gas chromatograph (Hewlett-Packard Model 5840, Palo Alto, CA). Samples were drawn and analyzed from each exposure chamber four times per hour using an 8-port stream-select valve.

Duration of treatment / exposure:

103 weeks

Frequency of treatment:

6 hours per day, 5 days per week

Remarks:

Doses / Concentrations:
500, 1000, or 2000 ppm (ca. 1.5, 2.9, 5.9 mg/L)
Basis:
other: target conc.

No. of animals per sex per dose:

50

Control animals:

yes

Details on study design:

- Dose selection rationale: Based on mortality and increased incidences and severity of nasal lesions observed in the 4000 and 8000 ppm groups in the 13-week study, exposure concentrations selected for the 2-year inhalation study in rats were 500, 1000, and 2000 ppm.

Observations and examinations performed and frequency:

CLINICAL OBSERVATIONS
Clinical findings were recorded at 4 – weeks intervals in the 2-year study until week 91 and every two weeks thereafter.

BODY WEIGHT
Animals were weighed initially, weekly for 12 weeks , monthly thereafter until week 91 , every 2 weeks until study termination, and at the end of the studies.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Necropsy was performed on all animals.

HISTOPATHOLOGY: Yes
Complete histopathology was performed on all rats. In addition to gross lesions and tissue masses, the following tissues were examined: adrenal gland, bone with marrow, brain, clitoral gland, esophagus, heart, large intestine (cecum,colon, and rectum), small intestine (duodenum, jejunum, and ileum), kidney, larynx, liver, lung (and mainstem bronchi), lymph nodes (mandibular and mesenteric), mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, skin, spleen, stomach (forestomach and glandular), testis (with epididymis and seminal vesicle), thymus, thyroid gland, trachea, urinary bladder, and uterus.

Statistics:

The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958). The primary statistical method used for the evaluation of tumor incidence was logistic regression analysis (Dinse and Lagakos, 1983; Dinse and Haseman, 1986; McKnight and Crowley. 1984). Additional methods used included the life table test (Cox, 1972; Tarone, 1975), appropriate for rapidly lethal neoplasms and the Fisher exact test and the Cochran-Armitage trend test (Arrnitage, 1971; Gart er al.. 1979). Tests of significance included pairwise comparisons of each exposed group with controls and a test for an overall dose-related trend.

Clinical signs:

no effects observed

Mortality:

mortality observed, non-treatment-related

Description (incidence):

No differences in survival rates between exposed and chamber control rats were found and no clinical findings that could be attributed to isobutyraldehyde exposure were observed.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

The mean body weights of male and female rats were generally similar to those of the chamber controls throughout the study.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Nonneoplastic lesions related to test substance exposure were limited to the nose and consisted of squamous metaplasia of the respiratory epithelium, degeneration of the olfactory epithelium, and suppurative inflammation. Incidences of minimal to mild squamous metaplasia in 1,000 and 2,000 ppm males and females and in 500 ppm females were significantly greater than those in the chamber controls. Another lesion associated with test substance exposure was minimal to mild degeneration of the olfactory epithelium in 2,000 ppm males and females. The incidences of suppurative inflammation (rhinitis) in male and female rats exposed to 2,000 ppm were increased compared to the chamber controls.

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

No increase in neoplasm incidences that could be attributed to exposure to the test substance was observed in male or female rats.

Dose descriptor:

NOAEC

Effect level:

>= 5.9 mg/L air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No neoplastic effects observed

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

5 900 mg/m³

Study duration:

chronic

Species:

other: rats and mice

Quality of whole database:

Comparable to guideline study, according to GLP

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available information classification for carcinogenicity is not warranted in accordance with EU Classification, Labeling and Packaging of Substances and Mixtures (CLP) Regulation No. 1272/2008.

Additional information

Two 2-year inhalation studies were reported (NTP, 1999), performed according to GLP and similar to OECD guideline 451.

In the first study, 50 male and 50 female rats per group were exposed to vapour concentrations of 500, 1000 and 2000 ppm (= 1.5, 2.9 and 5.9 mg/L) for 6 hours per day, 5 days per week. No increase in neoplasm incidences occured. Non-neoplastic lesions were limited to local effects in the nose and consisted of squamous metaplasia of the respiratory epithelium, degeneration of the olfactory epithelium, and suppurative inflammation. Incidences of minimal to mild squamous metaplasia in 1000 and 2000 ppm males and females and in 500 ppm females were significantly greater than those in the chamber controls. Minimal to mild degeneration of the olfactory epithelium occurred in the 2000 ppm males and females. Incidences of suppurative inflammation (rhinitis) in both sexes exposed to 2000 ppm were increased compared to controls. The NOAEC for carcinogenicity was equal or greater than 2000 ppm.

 

In the second study, exposure of 50 male and 50 female mice per dose group to 500, 1000 and 2000 ppm (= 1.5, 2.9 and 5.9 mg/L) for 6 hours per day on 5 days per week also did not increase the incidence of neoplasms compared to control animals. As in the rat study local effects in the nose were the primary effect. The incidences of olfactory epithelial degeneration in 1000 and 2000 ppm males and females were significantly greater than in the chamber controls. The NOAEC for carcinogenicity was equal or greater than 2000 ppm.