Pentane-2,4-dione

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Conduction and documentation of study acceptable. Literature reference and study report available.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1985

Reference 2

Reference Type:

secondary source

Title:

Unnamed

Year:

2001

Reference 3

Reference Type:

publication

Title:

Unnamed

Year:

1986

Reference 4

Reference Type:

publication

Title:

Unnamed

Year:

1995

Materials and methods

Principles of method if other than guideline:

20 Male and 20 female rats per group, with half being sacrificed at the end of exposure period and the remaining after a 4 week recovery period for the determination of the reversibility of observable effects, were exposed (whole body) to nominal concentrations of 0, 100, 300 and 650 ppm (corresponding to 0.409, 0.1226, 0.2656 mg/L) 2,4-pentanedione, respectively. Additionally 10 male rats were added to control and high dose groups for glutaraldehyde perfusion and subsequent ultrastructural examination of sciatic nerves.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Details on test material:

Purity: 99%
Lot No.: S874266

Test animals

Species:

rat

Strain:

other: COBS CDF F-344/CrIBR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc. (Kingston, NY)
- Age at study initiation: 34 days
- Housing: 2/cage (separated by sex and dose group)
- Diet: powdered food, Purina Certified Rodent Chow No. 5002, Ralston Purina Company, St. Louis, MO), ad libitum except during exposure
- Water: ad libitum except during exposure
- Acclimation period: 18 days in the laboratory, 2 days in the exposure chamber

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-26
- Humidity (%): 13-84
- Photoperiod: 12 hrs dark / 12 hrs light

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

not specified

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Liquid 2,4-pentanedione was metered from a piston pump into a heated glass evaporator. The resultant vapour was carried into the chamber by a countercurrent air stream that entered the bottom of the evaporator.
- Air flow rate: 1000 L/min
- Air change rate: 14/h
- Chamber volume: 4300 L
- Temperature, humidity: 23°C, 43-45% humidity

TEST ATMOSPHERE
- Brief description of analytical method used: The chamber concentrations of 2,4-pentanedione were analyzed by gas chromatography.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

2,4-pentanedione concentration in the exposure chamber measured every 33 min during the exposure. Analytical concentrations of 0, 101, 307, 650 ppm were observed.

Duration of treatment / exposure:

14 weeks

Frequency of treatment:

6 h/day, 7 days/week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
100, 300, 650 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0.409, 1.226, 2.656 mg/L
Basis:
other: nominal concentration, calculated according a formula given in Derelanko MJ, 2008, The Toxicologist´s Pocket Handbook, Second Edition

Doses / concentrations 3

Remarks:

Doses / Concentrations:
0, 101, 307, 650 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

20 Male and 20 female rats per group, with half being sacrificed at the end of exposure period and the remaining after a 4 week recovery period for the determination of the reversibility of observable effects.
Additionally 10 male rats were added to control and high dose groups for glutaraldehyde perfusion and subsequent ultrastructural examination of sciatic nerves.

Control animals:

yes, sham-exposed

Details on study design:

- Rationale for selecting satellite groups: Investigation of reversibility of effects.
- Post-exposure recovery period in satellite groups: 4 weeks.

Examinations

Observations and examinations performed and frequency:

Clinical signs of toxicity: daily
Ophtalmoscopy of the eye: prior to the first exposure and at sacrifice
Neurobehavioral screening: modified Irwin screen; monthly before, during and after exposure
Body weight: weekly during the study and before sacrifice
Food and water consumption for 15 h in metabolic cages during the last exposure week (urine collection)
Organ weights (liver, kidneys, lungs, brain, heart, thymus and testes), urine chemistry (n=10 each group), serum chemistry and haematology of blood samples collected at the end of exposure or the 4-week recovery.
Urine chemistry: Glucose, color and turbidity, ketones, protein, pH, blood, bilirubin, urobilinogen, volume.
Serum chemistry: creatinine, sodium, potassium, calcium, phosphorous, calcium, alanine aminotransferaae (SGPT), total protein, albumin, total bilirubin, conjugated and unconjugated bilirubin, aspartate aminotransferase (SGOT), globulin, urea nitrogen, carbon dioxde, creatinine phosphokinase, lactate dehydrogenase, sorbitol dehydrogenase, alkaline phosphatase, glucose, gamma-glutamyltransferase.
Hematology: leukocyte count, erythrocyte count, hemoglobin, hematocrit, mean corpuscular volume, platelet count, mean corpuscular hemoglobin, differential leukocyte smears, mean corpuscular hemoglobin concentration.

Sacrifice and pathology:

Gross pathology at termination in all groups.
Histopathology (nasal turbinates, larynx, trachea, lungs, epididymides, testes, spleen, thymus, urinary bladder, adrenal glands, brain (5 sections), thyroides, parathyroides, heart, kidneys, pituitary, skeletal muscle (gastronemius), stemal bone, spinal cord (lumbosacral region) and liver) in high dose, mid dose females and control group as well as brains of the mid dose group were processed for histopathology.

Results and discussion

Results of examinations

Details on results:

Analytical monitoring: No decomposition or chamber loss of the metered 2,4-pentanedione. Mean measured chamber concentrations were 0, 101, 307 and 650 ppm.
Toxicity results:
In the 650 ppm group all females and 10/30 male rats died between the 2nd and 6th week. Rats of this dose group had severe clinical abnormalities (e.g. lacrimation, ataxia, hypoactivity, hypothermia, encrustation in the perioral, perinasal abd periocular areas, incoordination, paresis).
Survivors of the 650 ppm group had decreased body weight gains, decreased absolute organ weights, but increased relative organ weights, and minor alterations in haematology (reduced hematocrit and hemoglobin and volume, increased lymphocytes), serum chemistry (increase in ureanitrogen and alkaline phosphatase activity, decrease in creatinine, calcium, and aspartate aminotransferase (AST) activity), and urinary chemistry (low pH (6.0 vs 7.0 in controls), slightly increased bilirubin and urobilinogen).
Noteworthy lesions in animals that died after exposure to 650 ppm were acute degenerations in the deep cerebellar nuclei, vestibular nuclei and corpora striata and acute lymphoid degenerations in the thymus. Many of the male survivors in this group (7/15, non-recovery and recovery group combined; all females of this dose group had died) had gliosis and malacia in the same brain regions but no peripheral neuropathy, minimal squamous metaplasia in the nasal mucosa, and lymphocytosis. Most of the rats with microscopic findings in the brain show deficits abnormal midair righting reflex, impaired gait during the Irwin neurobehavioral screen after one month of exposure. The majority of rats that survived the first month of exposure to 650 ppm did not exhibit neurobehavioral signs. No degenerative changes were seen in the spinal cords and ultrastructural microscopic evaluation of sciatic nerves did not produce any evidence of a peripheral neuropathy. Most of the observed alterations in male rats of the 650 ppm group that survived the 14 weeks exposure regimen decreased in frequency and/or severity after the 4 weeks recovery period. Additionally there were no treatment related neurobehavioral signs of abnormality in rats examined following the 4-week recovery period. There were no substance related mortalities in the 300, 100 and 0 ppm groups. Also there was no evidence of clinical signs (including Irwin neurobehavioral screen) or histologic lesions in these rats. However, females of the 300 ppm group had slightly decreased body weight gains (final body weight 5% lower than controls) and in both sexes minor concentration related alterations in hematology, serum and urine chemistry were observed. Furthermore, these changes were completely reversible following a 4 weeks recovery period . In the 100 ppm group no differences from controls were detectable. In all surviving males the mean testes weights and testes weights expressed as % of organ weight determined on necropsy right at the end of the study were not different from controls in any treatment group . The same observation was made for animals of the recovery group. No histopathological changes were noted in the testes and epididymis in any dose group of surviving males examined immediately after study termination and after a 4 week recovery period, respectively. One/10 control animals of the recovery group was diagnosed with epididymitis. In male animals of the high dose group which died during exposure atrophy of the seminal vesicles were seen in four males and degeneration of the seminiferous tubules in two animals. In the female rats uterus, cervix and ovaries were subject to histopathological examination. No pathological findings were observable after gross and microscopical examination of uterus, cervix and ovaries in any treatment group immediately after study termination. In females of the recovery group ovarial cysts ("cystic ovarian bursa") were found in 2/10 animals of the control group but none in the treated groups. One/10 animals each of the control and intermediate dose group had changes in uterus size ("luminal ectasia") while 1/10 animals of the intermediate dose group had size changes in the cervix ("luminal ectasia").
In conclusion, the results of this study would support 100 ppm as the NOAEL, 300 ppm as the LOEL and 650 ppm as the LOAEL based on the reversibility of effects seen in the 300 ppm dose group.

Effect levels

1

Dose descriptor:

NOEC

Effect level:

0.409 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No differences compared to the control were observed.

2

Dose descriptor:

NOAEC

Effect level:

1.226 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Minor alterations in hematology, serum and urine chemistry parameters were observed. Alterations were reversible within the recovery group.

3

Dose descriptor:

LOAEL

Effect level:

2.656 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Mortality occurred.

Target system / organ toxicity

Critical effects observed:

not specified