Methyl acetate

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1999

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Methyl acetate

EC Number:

201-185-2

EC Name:

Methyl acetate

Cas Number:

79-20-9

Molecular formula:

C3H6O2

IUPAC Name:

methyl acetate

Details on test material:

Formula C3H6O2
Molecular Weight 74.08 g/mol
Description: Clear, colorless liquid

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Winklemann, 33178 Borchen
- Age at study initiation: Approximatley 6-7 weeks (males) and 8-10 weeks (females)
- Weight at study initiation: Approximately 160-200 g
- Housing: in fully airconditioned rooms in Makrolon cages (type 4) on soft wood granulate in groups of 5 animals
- Diet (e.g. ad libitum): Ssniff R/M-H (V1534)
- Water (e.g. ad libitum): tap water in plastic bottles, ad libitum
- Acclimation period: at least 5 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 3 C
- Humidity (%): 50 +/- 20 % (target)
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light): 12 hours


IN-LIFE DATES: From: 13 Oct 1998 (males) To: 09 November 1998 (males)
IN-LIFE DATES: From: 14 Oct 1998 (females) To: 10 November 1998 (females)

Administration / exposure

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

other: unchanged (no vehicle)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Monitoring of the test atmosphere via IR analysis yielded for the following results:
Group 75 ppm 350 ppm 2000 ppm
Mean (ppm) 75 353 2033
Range (ppm) 55-88 330-381 1855-2116

Chemical analyses of the test atmosphere yielded the following results:
Group 75 ppm 350 ppm 2000 ppm
Mean (ppm) 79 335 2018
Range (ppm) 76.7-83.4 321.4-367.3 1829.9 - 2208.8

Duration of treatment / exposure:

28 days/ 6 hours

Frequency of treatment:

5 days a week

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 ppm

Remarks:

nominal

Doses / concentrations 2

Dose / conc.:

75 ppm

Remarks:

nominal

Doses / concentrations 3

Dose / conc.:

350 ppm

Remarks:

nominal

Doses / concentrations 4

Dose / conc.:

2 000 ppm

Remarks:

nominal

No. of animals per sex per dose:

10 male / 10 female

Control animals:

yes, concurrent no treatment

Details on study design:

Post-exposure period: 1 day

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: several times a day (once a day on weekend and holidays)
- Cage side observations checked in table were included.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly

BODY WEIGHT: Yes
- Time schedule for examinations: twice weekly

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: weekly
- Dose groups that were examined: all

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at termination
- Anaesthetic used for blood collection: Yes (Intraperitoneal injection of 67 mg Ketamine hydrochloride + 6.7 mg Xylazine / kg bw)
- Animals fasted: No
- How many animals: all animals
- Parameters checked in table yes were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at termination
- Animals fasted: No
- How many animals: all
- Parameters checked in table were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: few days before termination of treatment
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Parameters checked in table in Section 5.6.4 were examined.

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: weekly
- Dose groups that were examined: all
- Battery of functions tested: compound related signs of neurological disturbances

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table)
HISTOPATHOLOGY: Yes (see table)

Statistics:

Evaluation was performed by I/S Research and Preclinial Development, Hoechst Marion Roussel Deutschland GmbH with the aid of a program package for the evaluation of toxicological studies. The calculation methods used are referred to on the computer printouts.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Description (incidence and severity):

No clinical signs (including neurological disturbances) attributable to the exposure methyl acetate were observed in the animals.

Mortality:

no mortality observed

Description (incidence):

No animal died during the course of the experiment.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

At the high concentration groups, the body weights were decreased in both sexes, particularly in males.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

At the high concentration groups, food consumptions were decreased in both sexes (males>females) without significant differences in the mean relative food consumption /kg bw/d,

Food efficiency:

effects observed, treatment-related

Description (incidence and severity):

The food efficiency was similar in animals from all groups, therefore the reduction of body weights were considered to be related to the reduced food consumption.

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

not specified

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

At the high concentration groups, the mean values of erythrocyte counts, hemoglobin and hematocrit were increased, while the total counts of leukocytes and lymphocytes were decreased for these groups.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Clinical chemistry examinations revealed a dose-related decrease of cholesterol levels gaining significance in both sexes at the high concentrations and in females at all dose groups.
Serum calcium concentrations were increased in both sexes at the high concentration.
The ALAT activities were slightly, but significantly increased in high concentration females (41 U/L vs. 34 U/L in controls). The increase of ALAT activity in rats is indicative for hepatocellular damage. In absence of any morphological lesion or any other corresponding change this was considered indicative for a minimal dysfunction of liver cells.

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

Females from the high concentration group showed significantly increases in urine volume and decreases in specific weight.

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

The behavior and general health condition of the animals were observed several times daily (on weekends and public holidays once daily).

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Due to the effect on body weights several absolute organ weights were decreased and relative organ weights were increased in high concentration males.
Animals from the high concentrations groups had increased adrenal weights in both sexes and decreased thymus weights in females.
Slight significant changes of adrenal and thymus weights were also observed in females of the intermediate concentration group.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

The toxicological significance of altered adrenal weight and reduced cholesterol levels was considered to be equivocal as no morphological abnormality of the adrenal was observed. It can be interpreted to indicate nonspecific toxic response e.g. due to stress.
However a specific response of the adrenal cortex cannot be excluded; data on the serum levels of steroid hormone concentrations were not generated. The red blood changes may indicate hemoconcentration due to treatment-related increased diuresis observed in high concentration females and/or reduced water consumption. This remains uncertain, because of missing data on the water consumption.
The increase of ALAT activity in rats is indicative for hepatocellular damage. In absence of any morphological lesion or any other corresponding change this was considered indicative for a minimal dysfunction of liver cells. The weight reduction of thymus and leucocytopenia/lymphopenia should be discussed to give hint on a possible immunosuppressive effect. This assumption seemed to be uncertain in view of the absence of morphological changes in the thymus or any other immune organ. Overall, there is a concern that diureses, minimal liver cell dysfunction, adrenal weight increase, and reduced serum cholesterol concentrations represented minimal adverse effects due to the methyl acetate treatment. Therefore the NOAEL for systemic effects was also derived to be 350 ppm (1.057 mg/l).

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

At necropsy, no compound-related macroscopic findings were observed. Only sporadic findings could be observed in one animal of group 1, 2, and 4, each.
The main histopathological findings were topical irritations of the olfactory epithelium in the conchae nasales (degeneration and necrosis of epithelium).
Histopathologic examinations revealed slight to moderate degeneration and necrosis of the olfactory epithelium (at level 3 out of 4 sections) of mainly all males and females exposed to the high concentration of methyl acetate.
Any other treatment-related abnormality was observed in any other organs and in any other dose group. As degeneration of the olfactory mucosa occurred at 2000 ppm, the NOAEL for local effect was estimated to be 350 ppm (1.057 mg/l).
No changes attributable to the exposure of the test compound were detected in the animals from the other groups.

Histopathological findings: neoplastic:

not specified

Effect levels

1

Key result

Dose descriptor:

NOAEC

Effect level:

350 ppm

Sex:

male/female

Basis for effect level:

other: see 'Remark'

2

Dose descriptor:

LOAEC

Effect level:

2 000 ppm

Sex:

male/female

Basis for effect level:

other: Impaired body weight gain, decreased food consumption and pathological changes in the olfactory epithelium.

Target system / organ toxicity

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

2 000 ppm

System:

respiratory system: upper respiratory tract

Organ:

adrenal glands

blood

erythrocyte development

leucocyte development

thymus

other: degeneration and necrosis of the olfactory epithelium

Treatment related:

yes

Dose response relationship:

yes

Applicant's summary and conclusion

Conclusions:

The subacute inhalational treatment of Sprague Dawley Rats with Methylacetat caused dose dependent alterations of the olfactory epithelium of the conchae nasales. The degeneration of the highly specified cells in the high dose (2000 ppm) revealed this organ as the target organ for Methylacetat. The epithelium of the mid dose (350 ppm) and low dose (75 ppm) animals is not affected.
Therefore, the No Obsered Adverse Effect Level (NOAEL) is 350 ppm methyl acetate for male and female Sprague-Dawley rats, equivalent to a concentration of 1057 mg/m3 air.

Executive summary:

Groups of 10 male and 10 female Sprague Dawley rats received methyl acetate by nose-only inhalation exposure at concentrations of 0, 75, 350 and 2000 ppm for a period of 28 days (6 hours per day, 5 days per week). One day after the last administration all animals were killed and necropsied.

Concentrations of the test compound in the respiratory aid were monitored several times daily via IR analysis. Additionally, chemical analyses were carried out at weekly intervals.

Behavior and state of health were observed daily in all groups. Body weights and food consumption were recorded twice weekly.

Hematological and clinical chemistry examinations were carried out at the termination of the study. Furthermore, urine analysis was performed at the termination of the study.

Blood levels of the test compound were determined at different times after cessation of the last exposure in order to characterize elimination kinetics.

During the necropsy the animals were examined for macroscopically visible abnormalities, the main organs weighed and the organ to body ratios calculated. many organs and tissues were processed for histopathological examination and checked for microscopically visible changes.

Body weights, hematological and clinical chemistry data, urine data, absolute and relative organ weights were analyzed with the aid of a statistical program to show differences compared with the controls.

Mean daily analytical concentrations of methyl acetate ranged from 55 -88 ppm (low concentration), 330 -381 ppm (intermediate concentration) and 1855 -2116 ppm (high concentration group) and thus were close to the target concentrations. Chemical analyses revealed mean concentrations of 79, 335, 2018 ppm, respectively.

No clinical signs attributable to the exposure methyl acetate were observed in the animals.

Toxicokinetic examinations revealed that the blood levels of methyl acetate were below the detection limit of 5 ppm immediately after the end of the exposure and thereafter.

Body weights were decreased in both sexes from the high concentration group, particularly in males. These groups showed also decreased food consumption. Body weights and food consumption remained unaffected by the exposure to the test compound in other groups.

Heamtological examinations revealed increases in erythrocyte counts, hemoglobin and hematocrit values in both sexes from the high concentration group. Leukocyte counts were decreased in these groups.

Clinical chemistry examinations revealed decreased cholesterol levels and increased calcium concentrations in both sexes from the high concentration group.

Due to the effect on the body weights several absolute organ weights were decreased and relative organ weights were increased in males from the high concentration group. Additionally, adrenal weights were increased in both sexes from the high dose group, thymus weights were decreased in females from the high concentration group. Slight changes in thymus and adrenal weights were still observed in females from the intermediate concentration group.

No compound-related macroscopic findings were observed at necropsy.

Histopathological examinations revealed degeneration and necrosis of the olfactory epithelium of mainly all male and female animals from the high concentration group. No changes attributable to the exposure of the test compound were detected in the animals from the other groups.

In conclusion, repeated exposure of Sprague Dawley rats to methyl acetate at the concentration of 2000 ppm cause impaired body weight gain, decreased food consumption and pathological changes of the olfactory epithelium. The toxicological relevance of the clinical chemistry findings remain unclear. The same applies to the hematological findings, for which an explanation could be hemoconcentration or oxygen deficit. Adrenal weights were increased in both sexes, possible reflecting stress of the animals caused by exposure to an irritant concentration of the test compound. Thymus weights were decreased in females. However, there were no changes observed by histopatholgical examination of adrenals and thymus.

At the concentration of 350 ppm, slight increases in adrenal weights and slight decreases in thymus weights were observed in females. As there were no histopathological changes in these organs even at the much higher concentration of 2000 ppm, these findings are considered not to be of toxicological relevance.

With regard to the present study, the No Obsered Adverse Effect Level (NOAEL) is 350 ppm methyl acetate for male and female Sprague-Dawley rats, equivalent to a concentration of 1057 mg/m3 air.