Isobutyl methacrylate

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:

other: see 'Remark'

Remarks:

Study was conducted in accordance with a recognized scientific procedure for determining the toxicity of a test substance when administered repeatedly via inhalation for 4 weeks to experimental animals. Study was conducted in compliance with GLP regulations. The study meets national and international scientific standards (OECD 412) and provides sufficient information to support the conclusions regarding the NOAEC and the LOAEC demonstrated from the study data.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1993

Report date:

1993

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Butyl methacrylate

EC Number:

202-615-1

EC Name:

Butyl methacrylate

Cas Number:

97-88-1

Molecular formula:

C8H14O2

IUPAC Name:

butyl methacrylate

Details on test material:

- Supplier: Dupont, Belle plant, Belle, West Virgina, UAS
- Name of test material (as cited in study report): Butyl methacrylate
- Physical state: liquid > 99%
- Analytical purity: > 99%
- Impurities (identity and concentrations): no data
- Purity test date: no data
- Lot/batch No.: SWF90319

Test animals

Species:

rat

Strain:

other: Crl:CD BR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Kingston, Stone Ridge, NY, USA
- Age at study initiation: 35-day old
- Weight at study initiation: ca 260 g for males and ca 195 g for females
- Housing: individually in suspended wire-mesh cage in the inhalation chamber rooms
- Diet (e.g. ad libitum): Purina certified rodent chow 5002 (excepted during exposure)
- Water (e.g. ad libitum): tap water (excepted during exposure)
- Acclimation period: two weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 - 27
- Humidity (%): 40 - 60
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

All chambers were operated  at an air flow rate of 400 L/min, resulting in a calculated 99% aerosol  equilibrium time of 23 minutes or 6.4% of the exposure time. Vapors of the test material were generated  from the liquid form, introduced at a constant flow into heated flasks  (approx. 102-105 degrees C) through which a constant flow of air was  metered.  The inhalation chambers were stainless steel, approximately  2000 L. Chamber temperature was 22.8-25.5 degrees C; chamber relative  humidity was 62.5-67.6%.  Fresh air was mixed with the test chemical  vapors to achieve the desired concentration. 
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: The animals received a whole-body inhalation exposure under dynamic conditions in 2000-L stainless steel, glass, and Plexiglas® chambers.
- Method of holding animals in test chamber: Each animal was individually housed in a suspended wire-mesh cage without food or water during the exposure. Cage positions within the chambers were rotated each day to insure that the animals were exposed at several different locations within each chamber.
- Source and rate of air: Calibrated flowmeters (Fisher-Porter Inc., Warminster, PA) delivered compressed air at a rate of 30 L/min into the air inlet of each flask
- Temperature, humidity, pressure in air chamber: The mean temperatures and relative humidities for all four chambers ranged from 22.8 to 25.5°C and 62.5 to 67.6%, respectively.
- Air flow rate: The chamber volume and air flow rate were adjusted to reach 99% of the maximum vapor concentration (t99) within 30 minutes of the total exposure time (Silver, 1946). The volume of animais loaded into the chamber was Iess than 7% of the total chamber volume.
- Air change rate: no data
- Generation of the Test Atmosphere: The test material vapor concentrations were generated by metering the test material with calibrated Fluid Metering Pumps into 500 or 5000 ml three-necked round bottom flasks. The flasks were located in hemispherical heating mantles.
- Method of particle size determination: not appropriate, only vapors were generated
- Treatment of exhaust air: no data

TEST ATMOSPHERE
- Brief description of analytical method used: The concentration of butyl methacrylate in the chambers was determined using a Miran 1A gas analyzer attached to a strip chart recorder. Before the initiation of the exposure, the Miran 1A gas analyzer was callbrated using precisely measured amounts of butyl methacrylate delivered into a dynamic vapor generator. A calibration curve was generated to convert the readings obtained from the Miran 1A gas analyzer into parts-per-million (ppm) butyl methacrylate.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analytical  concentrations only of test material were determined throughout the  study.  Test concentrations were measured during each daily exposure  period (every 80 minutes) and the vapors analyzed by GC to confirm  purity. 

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

6 hr/day, 5 days/week

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 310, 952 and 1891 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control:

not appropriate

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed before and after each daily exposure for general condition and signs of toxicity, and once during the post-exposure observation period.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: Each animal was weighed weekly.

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

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: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: during necropsy at conclusion of study
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- How many animals: all animals
- Parameters examined: hematocrit, platelet count, hemoglobin, mean ceil volume, red blood cell, mean ceil hemoglobin, white blood cell count, mean cell hemoglobin conc.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: during necropsy at conclusion of study
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- Parameters examined:
triglyceride globuiin
cholesterol albumin : globulin ratio
blood urea nitrogen creatinine
glucose bilirubin (total)
alkaline phosphatase calcium
total protein inorganic phosphorus albumin
chloride sodium
potassium
glutamic pyruvic transaminase/alanine aminotransferase activity
glutamic oxaloacetic transaminase/aspartate aminotransferase activity
gamma-glutamyl transferase activity

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

ORGAN WEIGHTS: Absolute and relative organ weights (organ-body), measured at necropsy, included: adrenals, brain, kidneys, liver, lungs, and testes.

GROSS PATHOLOGY: Full compliment of tissues, including all male and female reproductive organs, were fixed and examined in all animals.

HISTOPATHOLOGY: The following tissues and organs were examined histologically in the high dose and control groups only: adrenals, gross lesions, heart, kidneys, larynx, liver, lungs, nasal cavity, spleen and trachea. Only identified target organs were to be examined in mid and low dose groups. Slides were stained with hematoxylin and eosin

Statistics:

Distribution of body weight, body weight changes,  and organ weight were inspected for normality and homogeneity of variance  across all dose groups.  Analysis of variance models were used to assess  the presence or absence of an overall compound effect. Separate one-way  models were used within the male and female data to assess overall  treatment group effects.  Two-way models were used for treatment group,  sex and interaction between groups. Pairwise comparisons of least square  means between control and treated groups were evaluated using  Dunnett'st-test.  Hematology and clinical chemistry values were inspected  for normality and homogeneity using ANOVA. Statistical significance was  demonstrated at the p < 0.05. 

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No deaths were noted at any concentration tested. The only treatment-related signs of toxicity observed were inactivity, lacrymation, eye squinting, and labored breathing. These signs were seen only during the six-hour exposure. Slight inactivity occurred in all butyl methacrylate exposed groups on days 1, 2, and 3. Inactivity to slight inactivity occurred at concentrations of 952 and 1891 ppm on days 4 through 20. Lacrymation was observed only twice during the first three days, once at 952 ppm and once at 1891 ppm. Eye squinting occurred only at the highest concentration from day 3 to day 20, with the exception of day 4, were no eye squinting was observed. Labored breathing occurred once during day 1, at 1891 ppm.

BODY WEIGHT AND WEIGHT GAIN
A statistically significant increase in the body weight for the 310 ppm females was observed during Week 3. However, because this was an isolated finding, and no concentration-related trend was observed, it was judged not to be treatment-related.

FOOD CONSUMPTION
A statistically significant decrease in the feed consumption for the 1891 ppm females was observed during Week 1. However, because this was an isolated finding, and no effect on body weight was observed, it was judged not to be treatment-related.

HAEMATOLOGY
No treatment-related differences in hematology parameters were observed.

CLINICAL CHEMISTRY
The clinical chemistry data showed two parameters with statistically significant findings. A decrease in the alkaline phosphatase concentration for 310, 952, and 1891 ppm female animals, was observed. A statistically significant decrease in the triglyceride concentration for 952 ppm and 1891 ppm female animals, was also observed. Although these parameters were statistically different from the controls in a concentration-related trend, these findings were judged not to be of toxicological significance.

ORGAN WEIGHTS
The organ weight data showed a statistically significant increase in kidney weight to body weight ratio in males and females exposed at 1891 ppm. Absolute kidney weights for this group were not statistically different from the controls.

GROSS PATHOLOGY
no data

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathologic evaluation revealed treatment-related observations in the nasal cavities. Microscopic examination of the nasal cavities of male and female rats exposed to 1891 ppm had slight and localized bilateral degeneration of olfactory epithelium lining the dorsal meati. One male rat and one female rat exposed to 952 ppm had similar changes in the olfactory epithelium. Rats exposed to 310 ppm had no exposure related nasal cavity microscopic changes.

Effect levels

1

Dose descriptor:

NOAEC

Effect level:

310 ppm

Sex:

male/female

Basis for effect level:

other: 1801 mg/m3 for local effects in the nasal olfactory epithelium

2

Dose descriptor:

NOAEC

Effect level:

1 891 ppm

Sex:

male/female

Basis for effect level:

other: systemic effects

3

Dose descriptor:

LOAEC

Effect level:

952 ppm

Sex:

male/female

Basis for effect level:

other: 5531 mg/m3, for local effects in the nasal olfactory epithelium

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

The no-observable adverse effect concentration (NOAEC) for systemic effects was 1891ppm. Based on histopathological changes seen in the nasal cavities, the no-observable adverse effect concentration (NOAEC) for local effects was 310 ppm.

Executive summary:

In an OECD Guideline 412 Repeated Dose 28-day inhalation study, 10 male and 10 female rats were exposed by whole body to 0, 310, 952 and 1891 ppm (0,1832, 5626, 11175 mg/m³) n-BMA for 6 hr/day, 5 days/week for 4 weeks. Treatment-related effects included lacrimation, eye squinting, and laboured breathing in the 952 and 1891 ppm (5626 and 11175 mg/m³) concentration groups throughout the study. There were no treatment-related effects on body weight or feed consumption, and no deaths occurred. Haematological measurements and clinical chemistry values generally were unaffected by treatment. Despite increased relative kidney weights at the high concentration (1891 ppm/11175 mg/m³) in both sexes, and slight increases in serum BUN values (resulting in increased BUN:creatinine ratio), histopathology of the kidneys was normal. The only treatment-related histopathological finding was localised bilateral degeneration of olfactory epithelium lining the dorsal meatus of the nasal cavity at 952 and 1891 ppm (5626 and 11175 mg/m³) in both sexes.