Pentane-2,4-dione

Endpoint summary

Description of key information

Repeated dose toxicity, subacute, oral, rat: NOAEL=100 mg/kg bw.
Repeated dose toxicity, subchronic, rat: NOAEC=0.417 mg/L (100 ppm).
Repeated dose toxicity, subacute, dermal, rabbit: NOAEL=244 mg/kg bw.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Adopted according to OECD SIDS (publicly available peer reviewed source). Original document not available.

Principles of method if other than guideline:

First experiment: 5 Rats per dose group were dosed with 0, 100, 500, or 1000 mg/kg bw of 2,4-pentanedione by gavage once a day. The doses were administered 1 to 11 times over a 1-15 day period. Controls received distilled water. In the 100 mg/kg bw dose group a 11th (lethal) dose of 1000 mg/kg bw was given.
Second experiment: An additional group of 5 male rats received 100 mg/kg bw of 2,4-pentanedione ten times over a 14 d period. 5 male control animals received 100 mg/kg bw of distilled water.

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

not specified

Sex:

not specified

Route of administration:

oral: gavage

Vehicle:

water

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

1-15 days

Frequency of treatment:

1-11 applications

Remarks:

Doses / Concentrations:
100, 500, 1000 mg/kg bw
Basis:
actual ingested

No. of animals per sex per dose:

5 rats per dose

Control animals:

yes, concurrent vehicle

Details on results:

First experiment:
1000 mg/kg bw: rapid onset of dyspnea and depression followed by prostration and death of all rats within 1 h after first dosing; no 2,4-pentanedione related changes at autopsy.
500 mg/kg bw: like high dose rats except that tremors and ataxia were observed; 3/5 rats died and 2/5 were sacrificed due to poor condition after 4 applications. Autopsy: 2/5 rats with poor haircoats, 1/5 distended bladder, congested lungs, clouding of cornea; histopathology: thymic necrosis (4/5), hepatocytes swelling and hepatic congestion (3/5), nephrosis (1/5), lymphadenitis in inesenteric lymph nodes (2/5), inflammation of the heart (3/5).
100 mg/kg bw: slight depression after applications (persisted 24 h in one rat which developed head tilt to the left side). All rats died after the final application of 1000 mg/kg or were sacrificed in moribund state. Histopathologically no 2,4-pentanedione related changes.

Second experiment: no differences between the 100 mg/kg dose group and the control group with regard to clinical signs, weight gain, hematology, clinical chemistry, organ weights, gross pathology and histopathology.

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

not specified

Basis for effect level:

other: No mortality occurred and no clinical signs were observed.

Critical effects observed:

not specified

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Principles of method if other than guideline:

Four groups, each consisting of 10 male and 10 female Fischer F-344 rats were exposed (whole body) 6 hours per day/5 days per week, for 9 days to 2,4 - pentanedione vapours (9 days exposure period interrupted by a two days non-exposure period after exposure day 5). 2,4-pentanedione concentration in the exposure chamber (nominal concentrations 0, 200, 400 and 800 ppm corresponding to actual mean concentrations of 0, 197, 418 and 805 ppm, respectively) measured every 33 min during the exposure. Clinical (every day prior, during and after exposure) and hematological (at sacrifice) parameters were determined, body weights and organ weights (liver, heart, brain, lungs, thymus, kidneys, testes) were measured. Necropsy was performed on each rat, histopathology on high dose and control animals only. In addition histopatholgic examination of nasal turbinates was performed in all dose groups.

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: COBS CDF F-344/CrIBR

Sex:

male/female

Details on test animals or test system and environmental conditions:

Age: 51 days

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

not specified

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

2,4-pentanedione concentration in the exposure chamber (nominal concentrations 0, 200, 400 and 800 ppm corresponding to actual mean concentrations of 0, 197, 418 and 805 ppm, respectively) measured every 33 min during the exposure.

Duration of treatment / exposure:

6 h

Frequency of treatment:

Once daily/5 days per week, for 9 days (9 days exposure period interrupted by a two days non-exposure period after exposure day 5)

Remarks:

Doses / Concentrations:
200, 400, 800 ppm
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0.817, 1.634, 3.269 mg/L
Basis:
other: nominal concentration, calculated according a formula given in Derelanko MJ, 2008, The Toxicologist´s Pocket Handbook, Second Edition

Remarks:

Doses / Concentrations:
197, 418, 805
Basis:
analytical conc.

No. of animals per sex per dose:

10

Control animals:

yes, sham-exposed

Observations and examinations performed and frequency:

Clinical signs: every day prior, during and after exposure
Hematology: parameters determined at sacrifice
Body weights and organ weights (liver, heart, brain, lungs, thymus, kidneys, testes) were measured

Sacrifice and pathology:

Necropsy on each rat. Histopathology on high dose and control animals only. In addition histopatholgic examination of nasal turbinates in
all dose groups.

Details on results:

Mortality: No animal died.
Clinical observation: Clinical signs of irritancy (partial eyelid closure, periocular and perioral wetness) were observed in few females of the 800 ppm exposure group; no exposure-related clinical signs in other groups.
Body weights: Transient body weight loss were observed during the first week of exposure in males and females of the 800 ppm group; significantly reduced body weight gain in both sexes at 800 ppm and in male rats at 400 ppm throughout the study; no body weight alterations in the 200 ppm dose groups.
Organ weights: Due to the body weight loss in 800 ppm exposure group absolute organ weights of brain, liver, kidney and lung/bronchi were lowered. The relative weights of these organs were within or higher than control values. Absolute and relative thymus weight in males and females of 800 ppm dose group were decreased (minus 15 %, statistically significant). Also the relative thymus weight in males of 400 ppm dose group was decreased, but not statistically significant (minus 11 %). No differences in organ weights in 200 ppm dose group.
Hematology: At 800 ppm significant leucocytosis in both sexes; statistically significant increase in lymphocyte count in male rats of high dose group; significant increased mean corpuscular hemoglobin concentration and mean corpuscular hemoglobin in male rats were within the range of historical control values. These alterations were not considered toxicologically significant by the study authors, because there was no effect in red blood cell count or in hemoglobin concentration. No changes in hematologic parameters were observable in animals of mid and low dose groups.
Histopathology: No treatment-related gross lesions; exposure-related inflammation of nasal mucosa, seen as multifocal areas of congestion, epithelial vacuolization, and lymphocyte or neutrophile infiltration of the submucosa, in all exposed rats; necrosis of the nasal mucosa frequently in 800 ppm rats, occasionally at 400 ppm and absent at 200 ppm; mild laryngitis in 2 male rats of the 800 ppm group. No lesions observable in the lower respiratory tract (trachea and lung). The biological significance of the mild vacuolization of the brain stem in two males of the 800 ppm group was not clear.

Dose descriptor:

NOAEL

Effect level:

0.817 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Dose descriptor:

LOAEL

Effect level:

1.634 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Necrosis of the nasal mucosa.

Critical effects observed:

not specified

Reference 2

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.

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

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

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

Remarks:

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

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

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.

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.

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.

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.

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.

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.

Critical effects observed:

not specified

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Principles of method if other than guideline:

New Zealand White rabbits were treated by 6 h occluded cutaneous application with undiluted 2,4-pentanedione at dose volumes of 0.25, 1.0 and 1.5 mL/kg bw (corresponding to 244, 975, 1463 mg/kg bw). Animals in the control group received occluded applications of Milli-Q filtered water at a volume of 1.5 mL/kg bw. The test or control substance was applied to the clipped dorsal surface of the rabbits. Twelve animals/sex/group were used for the control and high dose groups, 6 animals/sex/group for mid and low dose groups. The original study design included dosing for 5 days the first week and 4 day the second week. The additional 6 animals/sex/group in the controls and the high dose group were used for a 4 week recovery period. Due to mortality and signs of toxicity observable in mid and high dose groups, dosing was discontinued for these groups after day 4. Three surviving males and 2 surviving females from the high dose group were euthanized on day 4 while an additional 4 males and 3 females were retained without further dosing to day 12. Rabbits in the low dose group continued to receive a total of 9 doses (5 in the first week, 4 in the second). On day 12, 6 rabbits/sex from the control group were removed from the study since they were not required for their intended purpose as a recovery group. All other surviving rabbits were euthanized on day 12. Only 3 rabbits/sex from the control group were subjected to necropsy and histopathology. Monitors for toxicity included observations for clinical signs, including skin irritation, food consumption, water consumption, body weight and body weight change, organ weights, gross pathology and histopathology.

GLP compliance:

yes

Limit test:

no

Species:

rabbit

Strain:

New Zealand White

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: HRP, Inc . (Denver, PA)
- Age at study initiation: 15-18 weeks
- Weight at study initiation: 2.5 - 3.0 kg
- Fasting period before study:
- Housing: individual housing in stainless steel wire mesh cages
- Diet: Agway Prolab animal diet rabbit (Agway Inc.), ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 16-21
- Humidity (%): 40-60
- Air changes (per hr):
- Photoperiod: 12 hrs dark / 12 hrs light

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Details on exposure:

TEST MATERIAL
- Amounts applied: 0.25, 1, and 1.5 mL (244, 975 and 1463 mg/kg bw)
- Constant volume or concentration used: no

TEST SITE
- Type of wrap if used: gauze pads
- Time intervals for shavings or clipplings:

REMOVAL OF TEST SUBSTANCE
- Washing: After exposure the back of the animal was wiped with a damp cloth.

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

9 days

Frequency of treatment:

6 h/day

Remarks:

Doses / Concentrations:
244, 975 and 1463 mg/kg bw
Basis:
nominal per unit body weight

No. of animals per sex per dose:

6

Control animals:

yes

Observations and examinations performed and frequency:

Monitors for toxicity included observations for clinical signs, including skin irritation, food consumption, water consumption, body weight and body weight change, and organ weights.

Sacrifice and pathology:

3 rabbits/sex from the control group were subjected to necropsy and histopathology. Monitors for toxicity included observations for clinical signs, including skin irritation, food consumption, water consumption, body weight and body weight change, organ weights, gross pathology and histopathology.

Statistics:

The data for quantitative continuous variables were intercompared for the 3 treatment groups and the control group by use of Levene's test for equality of variances, analysis of variance (ANOVA), and t-tests. The t-tests were used when the F value from the ANOVA was significant. When Levene's test indicated similar variances, and the ANOVA was significant, a pooled t-test was used for pairwise comparisons. When Levene's test indicated heterogeneous variances, all groups were compared by an ANOVA for unequal variances followed, when necessary, by a separate variance t-test for pairwise comparisons.
Nonparametric data were statistically evaluated usinq the Kruskal-Wallis test followed by the Mann-Whitney U-test. Incidence data were compared using Fisher´s Exact Test. For all statistical tests, the probability value of < 0.05 (two-tailed) was used as the critical level of significance.

Details on results:

Occluded cutaneous dosing of rabbits with 2,4-pentanedione for 3 or 4 days resulted in death of 5/12 males and 7/12 females in the 1 .5 mL/kg bw (1463 mg/kg bw) group and 1/6 males and 3/6 females in the 1.0 mL/kg bw (975 mg/kg bw) group. Skin irritation was observed in all dose groups. Time to onset and severity of skin irritation were generally dose-dependent and persistent in all dose groups. Signs of skin irritation included erythema, edema, desquamation/exfoliation, excoriation, fissuring, necrosis and/or ecchymosis . In the mid and high dose groups of rabbits during the first few days of the study, several signs of systemic toxicity were evident. Numerous animals from these dose groups were hypoactive, uncoordinated and/or prostrate, had tremors, salivation, gasping and/or convulsions, and some had blue cutis of the nasal area suggestive of cyanosis. Furthermore, these groups lost mean body weight and food consumption decreased during the first few days of the study. After cessation of dosing in these dose groups, mean food consumption generally returned to control values while mean body weight gains were increased over control values. Excessive vocalization, slow or laboured breathing, and/or red perioral discharge were also observed in some high dose group animals until cessation of dosing. In the low dose group there were no mortalities, clinical signs of systemic toxicity, or effects on body weight or food consumption. Gross and microscopic evaluation at both day 4 and 12 confirmed dose-related skin irritation in all treatment groups. Microscopic lesions included acanthosis, subcutaneous edema, dermatitis, hemorrhage, congestion and/or necrosis. There were also numerous rabbits with hemorrhaging in various sections of the brain, including the meninges. Additionally, a number of brain sections showed neuronal degeneration, including the hypothalamus, mid brain, piriform cortex, pons and/or hippocampus. At both day 4 and 12, the thymus or thymic region, spleen, and/or lymph nodes of several animals of both sexes from the mid and high dose groups were congested and/or hemorrhaged; some animals also had lymphoid depletion or necrosis. This observation, combined with decreased lymphocyte and eosinophil counts in the high dose group at day 4, suggested possible effects on the immune system. Since the animals from the mid and high dose group had severe skin irritation and many signs of systemic effects a definitive conclusion regarding a treatment related response to the immune system is not possible, as discussed by the study authors. Except clinical pathology changes that may have been related to the skin irritation, no substance related differences from controls were reported in the low dose group.
According to the systemic effects observed, 244 mg/kg bw and 975 mg/kg bw correspond to the NOAEL and LOAEL of this dermal study, respectively.

Dose descriptor:

NOAEL

Effect level:

244 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Dose descriptor:

LOAEL

Effect level:

975 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Mortality occurred.

Critical effects observed:

not specified

Additional information

Repeated dose toxicity, oral:

In a subacute study two experiments were performed to assess the toxicity of the test substance after repeated exposure. In a first experiment 5 rats per dose group were dosed with 0, 100, 500, or 1000 mg/kg bw of 2,4 -pentanedione by gavage once a day. The doses were administered 1 to 11 times over a 1 -15 day period. Controls received distilled water. In the 100 mg/kg bw dose group a 11th (lethal) dose of 1000 mg/kg bw was given. The second experiment was performed to compare the 100 mg/kg bw dose group with control animals. Therefore, an additional group of 5 male rats received 100 mg/kg bw of 2,4-pentanedione ten times over a 14 d period. 5 male control animals received 100 mg/kg bw of distilled water.

The application of 1000 mg/kg bw led to rapid onset of dyspnea and depression followed by prostration and death of all rats within 1 h after first dosing. No 2,4 -pentanedione related changes were observed at autopsy. In the 500 mg/kg bw dose group the clinical signs were similar to the high dose group rats, except that tremors and ataxia were observed. 3/5 rats died and 2/5 were sacrificed due to poor condition after 4 applications. Autopsy revealed poor haircoats in 2/5 rats and distended bladder, congested lungs, clouding of cornea in 1/5 rats. After histopathology thymic necrosis (4/5), hepatocytes swelling and hepatic congestion (3/5), nephrosis (1/5), lymphadenitis of inesenteric lymph nodes (2/5), and inflammation of the heart (3/5) were observed. Dosing with 100 mg/kg bw led to slight depression after applications (persisted 24 h in one rat which developed head tilt to the left side). All rats died after the final application of 1000 mg/kg or were sacrificed in moribund state. Histopathologically no 2,4-pentanedione related changes were observed.

In the second experiment no differences between the 100 mg/kg dose group and the control group with regard to clinical signs, weight gain, hematology, clinical chemistry, organ weights, gross pathology and histopathology were observed. Thus a NOAEL of 100 mg/kg bw was deduced.

Repeated dose toxicity, inhalation:

In the key study Fischer rats (20 per group) were treated whole-body with vapors of 2,4 -pentanedione (nominal concentration: 100, 300, 650 ppm, corresponds to 0.409, 0.1226, 0.2656 mg/L) 6 h per day for 14 weeks (BRRC48-4, 1985). Half of the animals was sacrificed at the end of the study period, while the other half used as a satellite group for investigation of recovery of effects, and was sacrificed 4 weeks after the end of the main study. 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, serum chemistry, and urinary chemistry. 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 showed 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 (0.417 mg/L) as the NOAEC, 300 ppm (1.251 mg/L) as the LOEC and 650 ppm (2.71 mg/L) as the LOAEC based on the reversibility of effects seen in the 300 ppm dose group.

Another inhalation study is available were 10 male and 10 female Fischer F-344 rats were exposed (whole body) 6 hours per day/5 days per week, for 9 days to 2,4 - pentanedione vapours (Dodd, 1986). 2,4-pentanedione nominal concentration in the exposure chamber was 200, 400 and 800 ppm corresponding to 0.817, 1.634, 3.269 mg/L. No mortality was observed in any dose group.

Clinical signs of irritancy (partial eyelid closure, periocular and perioral wetness) were observed in few females of the 800 ppm exposure group but not in other groups. Transient body weight loss were observed during the first week of exposure in males and females of the 800 ppm group; significantly reduced body weight gain in both sexes at 800 ppm and in male rats at 400 ppm throughout the study and no body weight alterations in the 200 ppm dose groups.

The relative weights of brain, liver, kidney, and lung were within or higher than control values. Absolute and relative thymus weight in males and females of the 800 ppm dose group were decreased (minus 15 %, statistically significant). Also the relative thymus weight in males of the 400 ppm dose group was decreased, but not statistically significant (minus 11 %). No differences in organ weights in the 200 ppm dose group have been observed. At 800 ppm significant leucocytosis in both sexes, statistically significant increase in lymphocyte count in male rats of the high dose group, and significant increased mean corpuscular hemoglobin concentration were observed. Mean corpuscular hemoglobin in male rats was within the range of historical control values. By the study authors these alterations were not considered toxicologically significant because there was no effect in red blood cell count or in hemoglobin concentration. No changes in hematologic parameters were observable in animals of mid and low dose groups.

No treatment-related gross lesions were observed. Exposure-related inflammation of nasal mucosa, seen as multifocal areas of congestion, epithelial vacuolization, and lymphocyte or neutophile infiltration of the submucosa were observed in all exposed rats while necrosis of the nasal mucosa was observed frequently in 800 ppm rats, occasionally at 400 ppm and absent at 200 ppm. Mild laryngitis was observed in 2 males rats of the 800 ppm group. No lesions were observable in the lower respiratory tract (trachea and lung). A NOAEC of 200 ppm (0.817 mg/L) and a LOAEC of 400 ppm (1.634 mg/L) were deduced, based on the observation of necrosis of the nasal mucosa.

Repeated dose toxicity, dermal:

New Zealand White rabbits were treated dermally with 244, 975 and 1463 mg/kg bw, once daily (Ballantyne, 1986). Twelve animals/sex/group were used for the control and high dose groups, 6 animals/sex/group for mid and low dose groups. The study design included dosing for 5 days in the first week and 4 days in the second week. The additional 6 animals/sex/group in the controls and the high dose group were used for a 4 week recovery period. Due to mortality and signs of toxicity observable in mid and high dose groups, dosing was discontinued for these groups after day 4. Three surviving males and 2 surviving females from the 1463 mg/kg bw group were euthanized on day 4 while an additional 4 males and 3 females were retained without further dosing to day 12. Rabbits in the low dose group continued to receive a total of 9 doses (5 in the first week, 4 in the second). On day 12, 6 rabbits/sex from the control group were removed from the study since they were not required for their intended purpose as a recovery group. All other surviving rabbits were euthanized on day 12. Only 3 rabbits/sex from the control group were subjected to necropsy and histopathology. The occluded cutaneous dosing of rabbits with 2,4-pentanedione for 3 or 4 days resulted in death of 5/12 males and 7/12 females in the 1.5 mL/kg (1463 mg/kg) group and 1/6 males and 3/6 females in the 1.0 mL/kg (975 mg/kg) group. Skin irritation was observed in all dose groups. Time to onset and severity of skin irritation were generally dose-dependent and persistent in all dose groups. Signs of skin irritation included erythema, edema, desquamation/exfoliation, excoriation, fissuring, necrosis and/or ecchymosis. In the mid and high dose groups of rabbits during the first few days of the study, several signs of systemic toxicity were evident. Numerous animals from these dose groups were hypoactive, uncoordinated and/or prostrate, had tremors, salivation, gasping and/or convulsions, and some had blue cutis of the nasal area suggestive of cyanosis. Furthermore, these groups lost mean body weight and had decreased food consumption during the first few days of the study. After cessation of dosing in these dose groups, mean food consumption generally returned to control values while mean body weight gains were increased over control values. Excessive vocalization, slow or laboured breathing, and/or red perioral discharge were also observed in some high dose group animals until cessation of dosing. In the low dose group there were no mortalities, clinical signs of systemic toxicity, or effects on body weight or food consumption. Gross and microscopic evaluation at both day 4 and 12 confirmed dose-related skin irritation in all treatment groups. Microscopic lesions included acanthosis, subcutaneous edema, dermatitis, hemorrhage, congestion and/or necrosis. There were also numerous rabbits with hemorrhaging in various sections of the brain, including the meninges. Additionally, a number of brain sections showed neuronal degeneration, including the hypothalamus, mid brain, piriform cortex, pons and/or hippocampus. At both day 4 and 12, the thymus or thymic region, spleen, and/or lymph nodes of several animals of both sexes from the mid and high dose groups were congested and/or hemorrhaged; some animals also had lymphoid depletion or necrosis. This observation, combined with decreased lymphocyte and eosinophil counts in the high dose group at day 4, suggested possible effects on the immune system. Since the animals from the mid and high dose group had severe skin irritation and many signs of systemic effects a definitive conclusion regarding a treatment related response to the immune system is not possible, as discussed by the study authors. Except clinical pathology changes that may have been related to the skin irritation, no substance related differences from controls were reported in the low dose group. According to the systemic effects observed, 244 mg/kg bw and 975 mg/kg bw correspond to the NOAEL and LOAEL of this dermal study, respectively.

In conclusion, 2,4 -pentanedione revealed no specific toxicity after repeated exposure of test substance.

Justification for classification or non-classification

Dangerous Substance Directive (67/548/EEC)

- No classification required for repeated dose toxicity

  

Classification, Labeling, and Packaging Regulation (EC) No. 1272/2008:

- No classification required for specific target organ toxicity after repeated exposure through oral, dermal, and inhalation route.