Ethylbenzene

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline dose range finding study

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

2003

Reference 2

Reference Type:

publication

Title:

Ethylbenzene: 4- and 13-week rat oral toxicity

Author:

Mellert, W., Deckardt, K., Kaufmann, W., van Ravenzwaay, B.

Year:

2007

Bibliographic source:

Arch. Toxicol. 81:361-370

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)

Principles of method if other than guideline:

none

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Ethylbenzene

EC Number:

202-849-4

EC Name:

Ethylbenzene

Cas Number:

100-41-4

Molecular formula:

C8H10

IUPAC Name:

ethylbenzene

Details on test material:

- Name of test material (as cited in study report): Ethylbenzene
- Physical state: liquid

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ORGANISMS
- Species/strain: Rat Wistar (CrlGlxBrlHan:WI) (Charles River, Sulzfeld, Germany)
- Age at study initiation: 42 days +- 1 day
- Weight at study initiation:
- Number of animals: 5M+5F treated and controls.
- Housing: individually housed in suspended stainless-steel wire mesh cages
- Diet: ground Kliba maintenance diet mouse/rat (Provimi Kliba SA, Kaiseraugst, Switzerland), access ad libitum except during fasting period
- Water: access ad libitum expect during fasting period
- Environment: Temperature averaged 20-24 ºC; Relative Humidity averaged 30-70%

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

ADMINISTRATION / EXPOSURE
- Duration of test/exposure: 28 days
- Type of exposure: gavage
- Post exposure period: none
- Vehicle: cornoil
- Concentration in vehicle: 0, 0.75, 2.5 and 7.5 g/100ml.
- Total volume applied: 5 ml/kg
- Doses: 0, 37.5, 125 and 375 mg/kg administered twice daily to give the total daily doses of 75, 250 and 750 mg/kg/day bw.

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

Doses: 0, 37.5, 125 and 375 mg/kg administered twice daily to give the total daily doses of 75, 250 and 750 mg/kg/day bw

Duration of treatment / exposure:

28 days

Frequency of treatment:

twice daily 8 hours apart

Doses / concentrations

Remarks:

Doses / Concentrations:
75, 250 and 750 mg/kg bw/day
Basis:
other: nominal concentration

No. of animals per sex per dose:

5/sex/dose

Control animals:

yes, concurrent vehicle

Details on study design:

- Rationale for animal assignment: Random
- Post-exposure recovery period in satellite groups: None

Positive control:

Not applicable

Examinations

Observations and examinations performed and frequency:

- Clinical signs: twice daily weekdays, once a day a weekends, plus daily after each treatment.
- Mortality: as above
- Body weight: Prior to treatment, treatment day 0 an weekly thereafter
- Food consumption: Weekly
- Water consumption: Weekly (over 4 days)
- Ophthalmoscopic examination: no
- Haematology: leucocytes, erythrocytes, haemoglobin, haematocrit, MCV, MCH, MCHC, platelets, differential blood count, reticulocytes.
- Biochemistry: ALT, AST, ALP, GGT, Na, K, Cl, inorganic phopsphate, Ca, urea, glucose, total bilirubin, total protein, albumin, globulins, triglycerides, cholesterol, Mg
- Urinalysis: Day 26

Sacrifice and pathology:

ORGANS EXAMINED AT NECROPSY (MACROSCOPIC AND MICROSCOPIC):
- Organ weights: liver, kidneys, adrenals, testes, epididymes, ovaries, uterus, spleen, brain, heart, thymus
- Macroscopic: major organs, all gross lesions
- Microscopic: a range of major organs were fixed, liver and kidneys were examined microscopically. In addition to H&E staining the kidneys were stained with Mallory-Heidenhein stain to visualise hyaline droplet nephropathy.

Other examinations:

None

Statistics:

Analysis of body weight, body weight change, food and water consumption, and food efficiency was preformed by comparing treatment group results with the control group using Dunnett's test (two-sided) for the hypothesis of equal means. Clinical pathology except reticulocytes and differential blood count and organ weights were evaluated by nonparametric one-way analysis using two-sided Kruskal-Wallis test in combination with Wilcoxon test if resulting p value was <= 0.05. For urinalysis except volume, colour, specific gravity and turbidity a pair-wise comparison using Fischers exact test was used.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

effects observed, treatment-related

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

effects observed, treatment-related

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

effects observed, treatment-related

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

TOXIC RESPONSE/EFFECTS BY DOSE LEVEL:
- Mortality and time to death: No deaths.
- Clinical signs: Salivation was observed in high and mid dose rats of both sexes.
- Body weight gain: Significantly reduced in high dose males at day 7 (17.6% below control value)
- Food consumption: No treatment related changes.
- Food efficiency: Significant decrease in high dose males and females on day 28.
- Water consumption: Increased in high and mid dose rats of both sexes, attaining statistical significance over several time periods.
See the attachment-1 for details of water consumption.

- Clinical chemistry: Slight increase in serum ALT in high dose animals of both sexes. Increased bilirubin and cholesterol in high dose animals of each sex. Increase in bilirubin not statistically significant in males. Increased serum urea was observed in high dose males and reduced sodium levels in high dose females
- Hematology: No treatment related changes in hematological and clotting parameters.
- Urinalysis: Increased incidence of granular and epithelial cell casts in top and mid dose males together with an increased number of degenerated transitional epithelial cells in high dose males.
- Organ weights: Increased absolute and relative liver weights in both sexes at the high and mid dose levels. Increased relative kidney weights in top and mid dose males.
See the attachment-1 for details of and organ weight data.

Significant differences in epididymal and spleen weights were regarded as incidental.
- Gross pathology: No treatment related changes.
- Histopathology: Liver-centrilobular hepatocellular hypertrophy in top dose males and females and mid dose males. Hyaline droplet nephropathy (HDN) in the male kidney at all dose levels. Incidence: At top and mid dose levels HDN occurs in all males’ vs. 1 in control and at 75 mg/kg the incidence was 3 males treated vs. 1 in controls.

Effect levels

Dose descriptor:

NOAEL

Effect level:

75 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: The NOAEL in this range finding study was 75 mg/kg/day based on increased liver weight and hepatocellular hypertrophy at higher dose levels.

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

None

Applicant's summary and conclusion

Conclusions:

The NOAEL in this range finding study was 75 mg/kg based on increased liver weight and hepatocellular hypertrophy at higher dose levels. There was evidence of male rat specific nephropathy in high and mid dose groups which is not considered of relevance to man.

Executive summary:

Four matched groups of five male Wistar rats each were given by intubation repeated oral doses, 0,75, 250 and 750 mg/kg/day body weight of ethyl benzene in corn oil solutions for a period of 28 days twice daily 8 hours apart. Rats were housed individually in stainless steel cages with wire bottoms. Ground Kliba maintenance diet rat (Provimi Kliba SA,) was supplied to rats and tap water supplied to rats adlibitum except during fasting period.

Monitored for effects included clinical observations, body weights, opthalmoscopy, food consumption, hematology, clinical chemistry, urinalysis, necropsy, organ weights, gross pathology and histopathology.

 

There were no mortalities were observed during 28 day administration period. Salivation was observed in high and mid dose rats of both sexes. In body weights significantly reduction in high dose males at day 7 (17.6% below control value). There were no treatment related changes in feed consumption.
 Food efficiency shows significant decrease in high dose males and females on day 28. Water consumption is increased in high and mid dose rats of both sexes, attaining statistical significance over several time periods.


No treatment related changes in hematological and clotting parameters. Slight increase in serum ALT in high dose animals of both sexes. Increased bilirubin and cholesterol in high dose animals of each sex. Increase in bilirubin not statistically significant in males. Increased serum urea was observed in high dose males and reduced sodium levels in high dose females.

 

Urinalysis shows increased incidence of granular and epithelial cell casts in top and mid dose males together with an increased number of degenerated transitional epithelial cells in high dose males.

 

Increased absolute and relative liver weights in both sexes at the high and mid dose levels...Increased relative kidney weights in top and mid dose males. Significant differences in epididymal and spleen weights were regarded as incidental

There were no treatment-related gross pathology findings in either sex of rat. Liver-centrilobular hepatocellular hypertrophy in top dose males and females and mid dose males. Hyaline droplet nephropathy (HDN) in the male kidney at all dose levels. Incidence: At top and mid dose levels HDN occurs in all males’ vs. 1 in control and at 75 mg/kg the incidence was 3 males treated vs. 1 in controls.

 

 

The NOAEL in this range finding study was 75 mg/kg based on increased liver weight and hepatocellular hypertrophy at higher dose levels. There was evidence of male rat specific nephropathy in high and mid dose groups which is not considered of relevance to man.