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Acute Toxicity: inhalation

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acute toxicity: inhalation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
05 Aprll -18 May 2007
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: based on guidelines and GLP requirements

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
according to
OECD Guideline 403 (Acute Inhalation Toxicity)
GLP compliance:
yes (incl. certificate)
Test type:
standard acute method
Limit test:

Test material

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

Details on test animals and environmental conditions:
- 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

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

Administration / exposure

Route of administration:
other: mixture of vapour and aerosol
Type of inhalation exposure:
nose only
Details on inhalation exposure:
Exposure equipment
Animals were exposed to the test atmosphere in a nose-only inhalation chamber, a
modification of the chamber manufactured by ADO 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.
In our experience, 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.
4.6 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
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
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 (see Figure 1). 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 volume2 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.

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
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 l3.6, 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 NaHC03• During preliminary experimentation it was established that
a solution of NaHC03 performed at least as good as pure water and possibly better.
2 At ambient pressures varying from 1014 to 1022 hPa and temperatures in the exposure chamber in the
range 20-24°C, the flow varies from 21.3 to 21.8 Llmin

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 NaHC03 • 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 NaHC03 or water. Part of the samples were
stored at TNO for possible analysis of Cl-content (which was later cancelled), and the
remaining part of the samples was taken to Akzo Nobel (Arnhem) on the day of
sampling (19 October 2007; see Annex 3 for results).
4.7.2 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).
4.7.3 Particle size measurement
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 (see also 4.7.1), 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 mg/m) Based on our 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.
Analytical verification of test atmosphere concentrations:
Duration of exposure:
ca. 4 h
512 (± 150) mg/m3 and 1268 (± 77) mg/m3
No. of animals per sex per dose:
5 animals per sex per dose
Control animals:
Details on study design:
- Duration of observation period following administration: 14 days (or other?) 15 days
- Behaviour, clinical sign, breathing pattern and mortality
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
not specified

Results and discussion

Effect levels
Dose descriptor:
Effect level:
> 1 268 mg/L air (analytical)
Based on:
test mat.
Exp. duration:
4 h
Clinical signs:
other: 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 sl
Body weight:
Gross pathology:
No abnormalities
Other findings:

Applicant's summary and conclusion

Interpretation of results:
relatively harmless
Migrated information Criteria used for interpretation of results: not specified
LD50 > 1268 mg/L air (analytical)