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Acute Toxicity: inhalation

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Administrative data

Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
05 Aprll -18 May 2007
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2007
Report Date:
2007

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Test type:
standard acute method
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report):Monochloroacetic acid
- Physical state: white flakes
- Analytical purity:99.6%
- Lot/batch No.:07.02.277/048492
- Expiration date of the lot/batch: 17 february 2008
- Storage condition of test material: ambient temperature

Test animals

Species:
rat
Strain:
Wistar
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: charles river Deutschland, Sulzfeld, germany
- Weight at study initiation; mean group A: 322 and 198 g male and female, group B: 216 and 153 g male and females
- Fasting period before study: no
- Housing:macrolon cages with wood shavings as bedding, 5 males or 5 females per cage
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: at leats five days

ENVIRONMENTAL CONDITIONS
- Temperature (°C):22
- Humidity (%):65
- Air changes (per hr): approx 10 times per hour
- Photoperiod (hrs dark / hrs light): 12 / 12

Administration / exposure

Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Vehicle:
water
Remark on MMAD/GSD:
A particle size distribution measurement of the particles in the test atmosphere was attempted during preliminary experiments using a 10—stage cascade impactor (Andersen, Atlanta, USA). However, the results were unreliable, which is to be
expected with a volatile and hygroscopic test material, also because of the much longer sampling duration needed. Also, when using an APS (Aerodynamic Particle Sizer Model 3321, TSI Incorporated, Shoreview MN, USA), results were not
reliable as only about 1% of the nominal concentration was reported in the APS results (12 versus ca. 1200 trig/1113). Based on the lab's experience with the test atmosphere generation system chosen, primary droplets of about 10 microns were expected; the APS results (although not reliable) showed particles in the range of 3 to 20 microns.
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
Exposure equipment
Animals were exposed to the test atmosphere in a nose-only inhalation chamber, a modification of the chamber manufactured by ADG Developments Ltd., Codicote, Hitchin, Herts, S04 8UB, United Kingdom (see Figure 1). The inhalation chamber consisted of a cylindrical stainless steel column, surrounded by a transparent cylinder. The column had a volume of ca. 50 litres and consisted of a top assembly with two mixing chambers, underneath a rodent tube section and the exhaust section at the bottom. The rodent tube section had 20 ports for animal exposure. Several empty ports were used for test atmosphere sampling, particle size analysis, measurement of oxygen concentration, temperature and relative humidity. The animals were secured in plastic animal holders (Battelle), positioned radially through the outer cylinder around the central column. Male and female rats of each group were placed in alternating order. The remaining ports were closed. Only the nose of the rats protruded into the interior of the column.
Because the animal's body does not exactly fit in the animal holder which always results in some leakage from high to low pressure side. By securing a positive pressure in the central column and a slightly negative pressure in the outer cylinder, which encloses the entire animal holder, air would leak from nose to thorax rather than from thorax to nose. In this way, dilution of test atmosphere at the nose of the animals is prevented. The positive pressure was automatically set by a feedback system consisting of a pressure transducer in the inhalation chamber and a controlled valve in the exhaust of the chamber.

Generation of the test atmosphere
The present study was performed to allow proper classification for transport purposes of the solid form of MCA (flakes). Due to its hygroscopic properties it is very difficult if not impossible to generate respirable MCA dust from milled flakes. MCA particles in air are likely to equilibrate their water content with the ambient humidity and conversely, when generated as droplets from a solution, MCA will form hydrated particles when the water evaporates. In addition, MCA has an appreciable vapour pressure, therefore a test atmosphere containing respirable dust particles will also contain MCA vapour. Conversely, low concentrations of respirable dust will quickly evaporate. Because of the solid form (flakes), it was therefore chosen to dissolve MCA in demineralised water and to nebulize the solutions rather than generating MCA vapour by passing air through heated (liquid) MCA.
The inhalation equipment was designed to expose rats to a continuous supply of fresh test atmosphere. The test material was dissolved in demineralised water at a concentration of 50 giL for the first pilot experiment and 500 giL for the other exposures.
The solutions were passed using a syringe pump (World Precision Instruments, Sarasota FL, USA; type SP220i) to a compressed-air driven atomizer (Schlick, Coburg, Germany, type 970/S). The resulting test atmosphere was directed downward through the mixing section of the chamber towards the animals. The exhaust was located at the bottom of the chamber. The compressed air for the atomizer was humidified and the flow was measured using a mass stream meter (Bronkhorst, The Netherlands). The setting of the pump was recorded at regular intervals (approximately each half hour) during the generation of the test atmosphere. The readings of the mass stream meter were recorded on a chart recorder.
The airflow through the exposure chamber during exposure was 20 nL/minute for all exposures, in which nL stands for normal litre, the volume at 273 K and 1013 Pa.
The animals were placed in the exposure chamber 53, 102, 119 and l3 min after the start of the generation of the test atmosphere for the first and second pilot and exposures A and B, respectively. With a ventilation of at least 24 times per hour, this was sufficient to allow equilibration of the concentration.

Analysis of the test atmosphere
During preliminary measurements it was established that total carbon measurements with a flame ionisation detector could not be used because the base line proved unstable and this could not be solved by inserting filters or heated sample lines. Similarly, gravimetric analysis could not be used because the weight of a flake of monochloroacetic acid is decreased by evaporation and increased by water uptake from the atmosphere. Similarly, the course of weight change of a gravimetric filter loaded with a (partially dried) aerosol of a solution of monochloroacetic acid in water behaved erratically.
It was therefore decided to sample test atmosphere containing a mixture of monochloroacetic acid vapour and aerosol in impingers and to determine the concentration captured by ion chromatographic analysis.
Representative samples were obtained by passing samples of 13.6, 1.46, 1.32 and 1.33 L test atmosphere (at flows of 0.68, 0.73, 0.66 and 0.67 Llmin) for pilot 1 and 2 and exposures A and B, respectively, through a cascade of two impingers filled with 1.5 mmol solution of NaHCO3. During preliminary experimentation it was established that a solution of NaHCO3 performed at least as good as pure water and possibly better.

The chromatographic system was calibrated using solutions of 0, 0.2, 0.5, 1, 2, 5, 10 and 20 mg/L MCA in a solution of 1.5 mmol NaHCO3. Eight measurements series were run and the coefficients of determination of the accompanying calibrations were between 0.9996 and 1.0000.
Test atmosphere concentrations were hence calculated by dividing the amount of monochloroacetic acid captured in the impinger by the amount of test atmosphere led through the impinger.
In addition, in order to investigate whether MCA-complexes (glycolic acid) would be present in the test atmosphere 500 g MCA dissolved in 1 L water was atomized and mixed with dry clean air. Additional samples were taken by passing samples at flows of about 0.7 Llmin for about 2 min, through a cascade of two impingers filled with either 1.5 mmol solution of NaHC03 or water. Two samples of each were taken. Also, two similar samples were obtained by passing clean air through two impingers in series filled with either 1.5 mmol solution of NaHCO3 or water. Part of the samples were stored at the Institute for possible analysis of Cl-content (which was later cancelled), and the remaining part of the samples was taken to the sponser on the day of sampling.

Nominal concentration
The nominal concentration was determined by the flow of test material (as set by the syringe pump) divided by the input air flow of the atomizer (as measured by the mass stream meter).

Analytical verification of test atmosphere concentrations:
yes
Duration of exposure:
4 h
Concentrations:
pilot A: 102 (± 15) mg/m3
pilot B: 588 (± 25) mg/m3
exposure A (main study): 512 (± 150) mg/m3
exposure B (main study): 1268 (± 77) mg/m3
No. of animals per sex per dose:
For pilot A and B: one animal/sex concentration
For exposure A and B: 5 animals/sex/concentration
Control animals:
no
Details on study design:
Duration of observation period following administration: 15 days
The rats were visually inspected just before exposure, for reactions to treatment during the exposure, shortly after exposure, and at least once daily during the observation period. Respiration was monitored before exposure and immediately after exposure during at least a 10 second interval in the animals of the pilot experiments and in the animals of exposure A. In the animals of exposure B, respiration was monitored before exposure and immediately after exposure during 10-20 seconds per minute for a 5 minute interval. Each rat was placed in a modified Battelle restraining tube with a water-wetted silicon diaphragm separating externally head and neck from thorax and abdomen. The restraining tube, with the rat inside, was subsequently placed in a double room plethysmograph. Thoracic movement was determined with a pressure device (Honeywell) in the body chamber. Breathing frequency, tidal volume, and mean ventilatory flow were determined by means of recording the pressure signal from the body chamber. The breathing patterns were assessed qualitatively.
Body weights of the animals were recorded just prior to exposure (day 0) and on days 7, 14 and 15.
Necropsy of survivors performed: yes
Statistics:
not required based on the data obtained

Results and discussion

Effect levels
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 1 268 mg/m³ air (analytical)
Based on:
test mat.
Exp. duration:
4 h
Mortality:
no
Clinical signs:
irregular respiration
Remarks:
See at other findings
Body weight:
Normal body weight gain
Gross pathology:
No abnormalities
Other findings:
Although observation of the rats was limited during exposure due to the stay in restraining tubes, breathing at a decreased rate (graded as slight) was seen in all animals at almost all hourly observation time points. Laboured breathing, also graded as slight,
was seen in both animals of the first pilot, in the female animal of the second pilot and in 3 out of 5 female animals of group A at the last or the last two observation time points. Shortly after exposure a slight gait disturbance was seen in the animals of the first pilot experiment. Shortly after the second pilot experiment the two animals were sluggish (moderate) and piloercction and blepharospasm (both severe) were seen. Surprisingly, such or other abnormalities were not seen shortly afier exposure in group A, exposed to a similar concentration or in group B, exposed to that concentration. During the 14—day observation peried abnormalities were not seen in any ofthe groups.
Immediately after exposure, breathing frequency tended to be decreased and tidal volume increased in the two animals of the first pilot experiment. Similarly, breathing frequency was decreased immediately after exposure in the animals of the second pilot
experiment and in the animals of exposure A and B. However, asymmetric patterns or apnoeas were not seen.

Applicant's summary and conclusion

Interpretation of results:
GHS criteria not met
Conclusions:
4-h LC50 > 1268 mg/m3 air (analytical)
Executive summary:

Mortality (or clinical signs) did not occur during the 14 -day observation period after both exposures. It is, therefore, concluded that the 4—hour LC50 is above 1268 mg/m3 for male and female rats.