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Repeated dose toxicity: inhalation

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Administrative data

short-term repeated dose toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
February 15, 1991 - April 12, 1991
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP study

Data source

Reference Type:
study report

Materials and methods

Test guideline
according to guideline
OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)
; not measured: consumption, haematological and clinical chemistry, organ weight determinations, and microscopical examination of tissues and organs other than the nose
GLP compliance:
yes (incl. QA statement)
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
Ethyl (S)-2-hydroxypropionate
EC Number:
EC Name:
Ethyl (S)-2-hydroxypropionate
Cas Number:
Molecular formula:
ethyl (2S)-2-hydroxypropanoate
Details on test material:
Batch number EK 3003

Test animals

Details on test animals or test system and environmental conditions:
- Source: Wistar rats (Hsd/Cpb:WU) were obtained from Charles River Wiga, Sulzfeld, FRG
- Age at study initiation: 5-6 weeks old at arrival in the Institute; 6-7 weeks old at the start of the treatment
- Weight at study initiation: 196.7 (males) and 143.4 (females)
- Fasting period before study: no, but during exposure both control and test animals had no access to food or water
- Housing: During the acclimatization period (days -7 until -1) and during the main part of the recovery period (days 31-56) the rats were housed in groups of five, separated by sex in suspended, stainless steel cages, fitted with wire mesh floor and front. During the exposure period the rats were housed individually in wire mesh stainless steel cages in a modified H 1000 multitiered inhalation chamber manufactured by Hazleton Systems Inc., USA
- Diet (e.g. ad libitum): except during exposure, the rats were provided ad libitum with the Institute's stock diet
- Water (e.g. ad libitum): except during ex[posure, the rats were provided ad libitum with community tap water.
- Acclimation period: 7 days

- Temperature (°C): generally between 20-24°C during exposure and between 19 and 25°C before and after exposure. Occasionely, levels of up to 25.5°C were reached
- Humidity (%): generally between 40-70%,and during several days in inhalation chamber C (75 mg/m³) values of up to 77%. In addition, due to wet cleaning activities the relative huidity exceeded the upper limit, the peaks reached up to 97% for about half an hour each time
- Air changes (per hr): 10 in the animal room, 17-18 in the inhalation chambers
- Photoperiod (hrs dark / hrs light): 12 hours light, 12 hours dark

IN-LIFE DATES: From: February 15, 1991 To: April 12, 1991

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
other: unchanged (no vehicle)
Remarks on MMAD:
MMAD / GSD: vapour
Details on inhalation exposure:
- Exposure apparatus: Animals were exposed to the test atmosphere in modified H1000 multitiered inhalation chambers manufactured by Hazleton Systems Inc., USA. The chambers have a pyramidal top and bottom. The chambers have been constructed of stainless steel with glass doors on two sides which allow observation of the animals during exposure.
- Method of holding animals in test chamber: The rats were housed individually in wire mesh stainless steel cages.
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: To generate the test atmospheres, metered amounts of ethyl lactate were transported by roller pumps (Watson-Marlow 502S/R) to pressurized air driven nebulizers (Lee dispenser, type 110 K, Lee Co., USA). The generated mixture of air and test material was diluted with filtered air till the required concentration was achieved. To allow all particles to mix with air and to evaporate, the animals were located in the cage unit at the right bottom level of each inhalation chamber. Animals in the control group were exposed to freshly filtered air under similar conditions as the test groups.
- Temperature, humidity, pressure in air chamber: The temperature fluctuated between 20-24°C during exposure. The relative humidity generally fluctuated between 40-70%, but during several days in inhalation chamber C (75 mg/m³) values up to 77% were reached. In addition, due to wet cleaning activities the relative humidity exceeded the upper limit, the peeks reaching maxima up to 97% for about half an hour each time. Each chamber was fitted with a micromanometer which showed the negative pressure inside (1-4 mm water column).
- Air flow rate: Total airflow through the chambers varied between 38 and 40 m³/hour.
- Air change rate: between 17 and 18 air changes per hour during exposure, otherwise 10 air changes per hour.

- Brief description of analytical method used: The concentration of the test material was determined by means of a total carbon analyser (Ratfisch RS 55, FRG). Test atmosphere samples were taken sequentially from each of the chambers at a location close to the cage unit in which the animals were housed. The samples were drawn through sampling lines and were passed via a controlled valves system (Kuax-Control, Kuhnke 61.000) to the total carbon analyser. The response of the total carbon analyser was recorded in scale units and converted into concentration values (mg/m³). To ensure that no test material would condensate during sampling transport the sampling lines and the valves system were heated. Each chamber was monitored approximately once each half an hour for about 7 minutes, resulting in about 12 measurements per concentration level per day.
- Samples taken from breathing zone: no
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
The concentration of the test material was determined by means of a total carbon analyser (Ratfisch RS 55, FRG). Before the start of the study the response of the flame ionization detector (FID) was calibrated by passing flows of 25, 75, and 200 mg/m³ over the FID. The calibration mixtures corresponding to these flows, were prepared by injecting known quantities of test material (0.7, 2.2, or 5.8 µl) in 40-L teflon bags, which were filled with 30 L of air. After evaporation of the test material and careful mixing with the air, samples were passed to the total carbon analyser. The response of the FID (in scale units) was recorded. The calibration procedure was repeated towards the end of the exposure period. Similar data were obtained.
Duration of treatment / exposure:
4 weeks
Frequency of treatment:
6 hours a day, 5 days a week
Doses / concentrationsopen allclose all
Doses / Concentrations:
Target exposure levels: 0, 25, 75 and 200 mg/m³
nominal conc.
Doses / Concentrations:
Mean daily concentrations: 0, 24 (± 1), 73 (± 5) and 202 (± 3) mg/m³
analytical conc.
No. of animals per sex per dose:
5. For the 0 and 200 mg/m³ dose levels 5 additional male and female rats per level were exposed to be studied for an additional 4 weeks after the end of exposure (recovory group)
Control animals:
yes, sham-exposed
Details on study design:
- Dose selection rationale: In a previous study, ethyl lactate was irritating and toxic to the lining epithelium of the nasal cavity at levels of 150, 600 and 2500 mg/m³. Clinical observations, growth, gross examination at autopsy and microscopical examination of the nose were used as criteria for disclosing possible harmful effects at lower concentrations of 25, 75 and 200 mg/m³.
- Rationale for animal assignment (if not random): One day before the start of the study, the rats were divided over the various groups in such a way that the mean initial body weight was about the same in all groups (< ± 20% of the mean weight). A few rats were replaced by reserve animals in order to equalize the mean initial body weight. Computer randomization according to body weight was not possible because the number of animals in each group was not the same (groups B and C comprised of less animals than groups A and B). Computer randomization was, however, performed upon arrival.
- Rationale for selecting satellite groups: To provide data on recovery from, persistence of, or delayed occurrence of toxic effects on the nose.
- Post-exposure recovery period in satellite groups: 28 days
- Section schedule rationale (if not random):On nominal day 28, all rats of the main groups, and on day 56, all rats of the recovery groups, were killed in such a sequence that the average time of killing was about the same for each group.
Positive control:


Observations and examinations performed and frequency:
- Time schedule: The general condition and behaviour of all animals were checked at least once daily throughout the study. All signs of ill health, reaction to treatment or mortality were recorded.

- Time schedule: Each rat was individually handled and carefully examined for clinical signs, abnormal behaviour or abnormal appearance at the weekly weighing.

- Time schedule for examinations: The individual body weights of all rats were recorded during the acclimatization period (day -4), one day before the start of the exposure (allocation procedure), just prior to the first exposure to the test substance (day 0), and subsequent at weekly intervals (including the day of autopsy).

- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No

- 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







Sacrifice and pathology:
GROSS PATHOLOGY: Yes. The animals were anaesthetized by ether, bled to death by cannulating the abdominal aorta and examined macroscopically for pathological changes.
HISTOPATHOLOGY: Yes. The nose of all animals was preserved in a neutral, aqueous, phosphate-buffered, 4% solution of formaldehyde, decalcified, embedded in paraffin wax, sectioned at 5 µm and stained with haematoxylin and eosin. Histopathological examination was performed on 4 sections of the nose of each animal.
Body weight data of the main groups were analysed by one-way analysis of covariance using preexposure (day 0) weights as the covariate. When group means were significantly different (p<0.05) individual pairwise comparisons were made using Dunnett's multiple comparison method. Body weight data of the recovery groups were analysed by Student t-test. Incidence of histopathological changes were analysed by Fisher's exact probability test. All pairwise comparisons were two tailed. Group mean differences with an associated probability of less than 0.05 were considered to be statistically significant.

Results and discussion

Results of examinations

Clinical signs:
no effects observed
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Histopathological findings: neoplastic:
not examined
Details on results:
The few observed gross changes are common findings in rats and they are not considered to have any toxicological relevance.

In a few rats of either sex of both the main and the recovery groups (controls included), the respiratory epithelium of the nasal cavity showed minimal changes, seen as nest-like infolds and slight hyperthrophy/hyperplasia. The changes were about equally distributed amongst the various groups or occurred in a single animal only. Therefore, the changes were not ascribed to inhalation of ethyl lactate.

Effect levels

Dose descriptor:
local effects
Effect level:
200 mg/m³ air (nominal)
Basis for effect level:
other: see 'Remark'

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

The NOAEC of ethyl lactate is 200 mg/m³ for local effects.
Executive summary:

In a subchronic inahlation toxicity study ethyl lactate was administered to 5 male and 5 female Wistar rats/concentration by whole body exposure at concentrations of 0, 0.025, 0.075 and 0.2 mg/L (0, 25, 75 and 200 mg/m³) for 6 hours per day, 5 days/week for a total of 28 days. Two additional (recovery) groups of 5 male and 5 female Wistar rats exposed to 0 or 0.2 mg/ were kept untreated for 28 post-exposure days. Clinical observations, growth, macroscopical observations at autopsy and microscopical examinations of the nose were used as criteria for disclosing possible harmful effects.

There were no compound related effects in mortality, clinical signs, body weight or gross and histological pathology. Microscopic examination revealed minimal changes (nest-like infolds, slight hypertrophy, and slight hyperplasia) in the nasal respiratory epithelium of animals in all groups, the control group included. Type and incidence of the changes were similar in the various groups, or the changes occurred in a single animal only. These changes were not ascribed to treatment.

The NOAEL is 200 mg/m³.