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Acute Toxicity: inhalation

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acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
6-hr exposure followed by 14-day observation period
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP study; study designed to be in compliance with EPA, OECD, ECC and J-MAFF test guidelines for acute inhalation studies.
Reason / purpose:
reference to other study

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
equivalent or similar to
other: This study was designed to comply with ECC, OECD, US-EPA, and J-MAFF test guidelines for acute inhalation studies
not specified
GLP compliance:
Test type:
standard acute method
Limit test:

Test material

Details on test material:
-Name of test material (as cited in study report): tertiary-butyl acetate; acetic acid, tert-butyl ester; TBAc
-Appearance: clear, colorless liquid
-Amount received: Forty liters
-Batch #: 1031267
-Purity: ≥ 95%
-Date received: 3/30/98
-Expiry date: > 1 year
-Source of test material: Arco Chemical Company (now LyondellBasell Industries)
-Storage conditions: in the dark at room temperature and humidity and in the original container.

Test animals

Details on test animals and environmental conditions:
-Source: Charles River UK Limited, Kent, England
-Animal receipt: 6/16 or 6/30/99
-Animals: 20/sex (5/sex/group)
-Age: young adults, approximately 7 (males) and 8 (females) weeks of age
-Acclimation period: at least 5 days
-Weight at Study Initiation: 246 - 283 grams (males) and 165 - 220 grams (females)
-Housing: In the holding area, rats were housed 5/cage/sex in suspended steel wire-mesh cages, except during exposure and an overnight post-exposure period when rats were kept in a ventilated cabinet to allow dispersal of residual test material.
-Bedding: no data
-Diet: SDS Rat and Mouse Diet (RMI); ad libitum in holding area; withheld during exposure
-Water: ad libitum in holding area; withheld during exposure
-Identification method: identified individually by a number tattooed on the ear pinnea
-Method of Animal Distribution: no data

-Room temperature (°C): 20.5 - 23.0
-Relative humidity: 43 - 65%
-Air changes: 12 - 15 times/hour
-Lighting Cycle: 12 hours light/12 hours dark

-Date of experiment initiation: 6/22/99
-Date of experiment termination: 7/21/99

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
nose only
other: chamber ventilation air
Details on inhalation exposure:
The vapor generator produced and maintained an atmosphere containing vapor by evaporation of the test material from a fritted glass disc with a countercurrent of air. The generator was partly immersed in water maintained at 40 °C in a water bath as an aid to evaporation.

To produce the vapor for exposure, a supply of clean dried air was connected to a vapor generator and the supply pressure was adjusted to give a flow rate of 15 liters/minute. The chamber exhaust was calibrated at the point of attachment to the exposure chambers and adjusted to give a slight negative pressure. In-line flow meters were used to monitor generator and exhaust airflow during the exposure. A syringe filled with the test substance was fitted to the syringe pump and connected to the generator. Feed rates were selected to produce target vapor concentrations of 2000, 3500, and 5000 ppm. Feed rates were adjusted during the exposure period as necessary. Rats to be exposed were placed into separate restraining tubes and then were attached to the exposure chamber. After an exposure period of six hours (following a 5 min equilibration period), the syringe pump was switched off and the exposure chamber was allowed to be cleared before rats were removed. The control group was treated similarly, but exposed to only air. Nominal concentrations of the test substance were calculated from the amount of tertiary butyl acetate delivered to the vaporizer and the total volume of air flowing through the exposure chamber during the period of generation. Temperature and humidity in the exposure chamber were also monitored and recorded.
Analytical verification of test atmosphere concentrations:
Duration of exposure:
6 h
For the target exposure concentrations of 2000, 3500, and 5000 ppm (9.49, 16.61 and 23.72 mg/L), the mean calculated chamber concentrations and (nominal concentrations) were 1873 (2133), 3502 (4062), and 5066 (5725) ppm, respectively.
No. of animals per sex per dose:
Control animals:
Details on study design:
Following exposure, rats were returned to the holding cages and food and water were restored. The test rats were kept in a ventilated cabinet overnight and then returned to the holding room for the remainder of the observation period. Control rats were returned to the holding room at the end of exposure.

Animals were observed for 14 days.

Mortality checks were performed once in the morning and then again towards the end of the working day.

The rats were observed continuously for test substance-related signs during the exposure period (6 hours) and at least twice daily throughout the observation period.

Individual body weights were recorded prior to exposure and daily thereafter.

Food and water consumption were measured daily, from the day after arrival to termination.

Animals found dead were necropsied as soon as possible. At termination of the 14-day observation period, surviving animals were euthanized and necropsied. All rats received a detailed macroscopic examination. Kidney, lung (including larynx and trachea), and liver weights were obtained during the gross necropsy. The estimated LC50 value was based on the survival rate during the study.
Means and standard deviations were calculated for chamber concentrations, body weights, and organ weights. The geometric mean of the mid- and high concentrations was used to determine the approximate LC50 (6-hr).

Results and discussion

Effect levels
Dose descriptor:
Effect level:
4 211 ppm
Exp. duration:
6 h
Remarks on result:
other: Deaths considered due to direct effects on lungs from exposure to irritant atmosphere. The LC50 (6-hr) was between 3502-5066 ppm (calculated based on analyzed chamber conc.); approximation of LC50 would be geometric mean of these values (4211 ppm).
All mortality occurred on the day of exposure. At the 5066 ppm exposure level, 3 males and 5 females died during exposure. The two remaining males were sacrificed at 1 hr after exposure because of a moribund condition. There were four female deaths during exposure to 3502 ppm. No other signs of mortality were observed during the study.
Clinical signs:
other: Abnormal clinical signs noted in one or more groups of test animals during or shortly (0 to 1 hour) after the exposure period included: unconsciousness; body cold to touch; exaggerated, noisy, and/or slow breathing; staggering; fine to whole-body tremors;
Body weight:
Body weight gain for surviving animals was largely unaffected by exposure to the test material.
Gross pathology:
Gross observations at necropsy of male and female animals that died included minimal to severe congested lungs, pale kidneys, and wetness and staining of the hair with excreta. For treated rats surviving the exposure period, findings at necropsy were limited to minimal to moderate congestion of the lungs for a single 3502 ppm group male and dark foci on the lungs for one 1873 ppm and two 3502 ppm group males; no gross abnormalities were observed in female rats. In the control group, pale raised areas on the lungs were noted for one female. There were no treatment-related effects on organ weights among exposure groups.
Other findings:
Food and water consumption for surviving animals were similar to control values throughout the observation period.

Any other information on results incl. tables


All mean analytical chamber concentrations (1873, 3502 and 5066 ppm, respectively) were in close agreement with the target concentrations of 2000, 3500 and 5000 ppm. The nominal concentrations were 2133, 4062 and 5725 ppm. The analyzed concentrations of tertiary butyl acetate were approximately 88%, 86% and 88% of the nominal concentrations, respectively. 

Applicant's summary and conclusion

Interpretation of results:
Category 4 based on GHS criteria
Migrated information
Under conditions used in this study, tertiary butyl acetate was harmful by the inhalation route in rats. In this study, a relatively steep mortality curve was evident for tertiary butyl acetate. No mortality was observed in either sex exposed to a concentration of 1873 ppm for 6 hours. Four of five females but no males exposed to 3502 ppm died during exposure and all animals exposed to 5066 ppm died during or shortly after exposure or were sacrificed in extremis by the 1 hour post-exposure observation. The deaths were considered by the study director to be due to the direct effects on the lung following exposure to an irritant atmosphere. Treatment-related clinical signs noted in one or more groups of animals during or shortly after exposure included one of more of the following: noisy and/or exaggerated breathing, cold body temperature, staggering, rapid shaking of the head and thorax, whole body tremors, walking on tips of toes, immobility, lethargy, and coma. All clinical signs in surviving animals resolved by Day 1. Mortality and severity of clinical signs occurred in a concentration-dependent manner. Under the conditions of this study, it is considered that the geometric mean of 4211 ppm approximates the 6-hour LC50.

Applying Haber’s Law to express the 6-hour LC50 value of 4211 ppm in terms of a 4-hour exposure, tertiary butyl acetate meets the criteria as Category IV for the UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and the EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008. A harmonized classification for tertiary butyl acetate exists; however, this hazard category is not currently included in Directive 67/548/ECC. A recommendation is made to add the classification for Acute Toxicity Category IV, "Harmful if inhaled" to Table 3.1 of Annex VI and R20 "Harmful by inhalation" to Table 3.2 of Annex VI. Based on clinical signs indicating reversible effects on the central nervous system and respiratory tract irritation, tertiary butyl acetate meets the criteria for Category 3 for classification and labeling under UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008 for Specific Target Organ Toxicity – Single Exposure (STOT-SE). A harmonized classification exists for tertiary butyl acetate; however, this hazard category is not included in Directive 67/548/ECC. A recommendation is made to add R37 – "Irritating to respiratory system" to Table 3.2 of Annex VI and STOT-SE Category 3, H-335 "May cause respiratory irritation" and H336- "May cause drowsiness or dizziness" to Table 3.1 of Annex VI.
Executive summary:

In an acute inhalation toxicity study, 5 rats/sex/group were exposed to tertiary butyl acetate at target concentrations of 0, 2000, 3500 and 5000 ppm for a period of 6 hours followed by a fourteen-day observation period. No animals died at the lowest concentration tested; all deaths in the mid- and high-exposure groups occurred on the day of exposure. During and following exposure, there was a concentration-dependent increase in respiratory tract irritation as well as severity of central nervous system effects that included staggering, rapid shaking of head and thorax, walking on tips of toes, whole body tremors, immobility, and lethargy. The adverse clinical signs resolved in all surviving animals within 24 hours following the end of the exposure. Gross observations at necropsy of animals that died on study as well as necropsy for treated rats surviving the exposure period indicated that tertiary butyl acetate caused respiratory tract irritation. Under the conditions of this study, the inhalation (6 hour) LC50 of tertiary butyl acetate in Sprague-Dawley albino rats was 4211 ppm for the combined sexes. Females were more sensitive than males based on deaths of four of five female animals but no males by the end of the 6-hr exposure period in the 3502 ppm exposure group.  Based on the results of this study, tertiary butyl acetate is harmful if inhaled.