Sodium chloroacetate

Endpoint summary

Description of key information

The information is based on monochloroacetic acid (MCA) which is a strong acid and dissociates in biological media; many studies have used monochloroacetic acid neutralized with sodium hydroxide or its sodium salt, so that data of monochloroacetate can be used to also evaluate the systemic toxicity for sodium monochloroacetic acid (and vice versa).

In a dermal toxicity study (see section 7.2.3) with rabbit skin it was shown, in addition, that the toxicity of MCA is not caused by a surplus of H+ ions and that the influence of pH appeared to be secondary, because its direct reaction to biomolecules was the primary cause of cytotoxicity.

Acute oral toxicity (based on MCA): Rat LD50  90 mg/kg bw,  standard acute toxicity method

Acute dermal toxicity (based on SMCA): Rat LD 50 3250 mg/kg bw (males); > 2000 mg/kg bw (females). Non-guideline, non GLP but similar to standard acute dermal toxicity test

Acute inhalation toxicity (based on MCA): Rat 4 -h LC50 >> 1286 mg/m3 in air. OECD 403, GLP.

With regard to dermal toxicity it was shown that SMCA is ca. 10 times less toxic than MCA.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1-29 March 1979

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 401 (Acute Oral Toxicity)

Principles of method if other than guideline:

Instead of 5 rats/sex/group, 10 females/group were used.

GLP compliance:

no

Remarks:

did not exist at that time

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

female

Details on test animals or test system and environmental conditions:

no data

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 1%
MAXIMUM DOSE VOLUME APPLIED: max 16 ml/kg

Doses:

40 mg/kg
63 mg/kg
100 mg/kg
160 mg/kg

No. of animals per sex per dose:

10 females/dose

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: weekly weighing and no data on observation scheme
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, macroscopic examination

Statistics:

not applicable

Sex:

female

Dose descriptor:

LD50

Effect level:

90.4 mg/kg bw

Based on:

test mat.

95% CL:

73.6 - 112

Mortality:

40 mg/kg 0/10
63 mg/kg 2/10
100 mg/kg 5/10
160 mg/kg 10/10

Clinical signs:

other: Animals which died during study: restless behaviour, uncoordinated movements, hunched posture, lethargy, lacrimation, piloerection, pulsing respiration. Surviving animals showed these symptoms at lower severity and recovered from all symptoms within 48 h

Gross pathology:

Surviving animals: no findings
Animals which died during the study showed red-brown and highly vascularised liver with patch pattern, red-pink lungs with foci. Spleen was black discolored at the stomach-side.

Interpretation of results:

Category 3 based on GHS criteria

Conclusions:

Oral LD50= 90.4 mg/kg

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

90 mg/kg bw

Acute toxicity: via inhalation route

Link to relevant study records

Reference

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

Qualifier:

according to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system 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

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

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.

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.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

discriminating conc.

Value:

1 286 mg/m³ air

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 January 1988 to 11 February 1988

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.3 (Acute Toxicity (Dermal))

Deviations:

no

GLP compliance:

yes

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

other: Wistar Hoe: WISKf(SPF71)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Hoechsty AG.
- Age at study initiation: males: approx. 7 weeks. Females: approx. 8 weeks
- Weight at study initiation: males: mean 213 grams (190-229 grams), females mean 209 grams (203-215 grams)
- Fasting period before study: no
- Housing: Individual housing in Macrolon Type 3 cages containing sawdust.
- Diet (e.g. ad libitum): ad libitum (Altromin 1324)
- Water (e.g. ad libitum): ad libitum ( tapwater)
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 3 degrees Celcius
- Humidity (%): 50 +/- 20%
- Air changes (per hr): not specified
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 21 January 1988 to 11 February 1988

Type of coverage:

occlusive

Vehicle:

physiological saline

Remarks:

ratio: 1.0 gram test substance + 0.36 ml vehicle

Details on dermal exposure:

TEST SITE
- Area of exposure: It was reported that a skin area op approx. 30 square cm was shaved, and a patch of 48 square cm was applied. This will likely have been incorrectly reported, i.e. the skin area shaved should likely read 48 square cm and the patch are should likely read 30 square cm.
- % coverage: not specified but considered to exceed 10% of body surface based on area of exposure and weight of rats.
- Type of wrap if used: elastic bandage, 8 cm wide.

REMOVAL OF TEST SUBSTANCE
- Washing (if done): yes, with tepid tapwater
- Time after start of exposure: after removal of the bandage.

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 1600, 2000 or 2500 mg test substance moistened in ratio 1.0 grams test substance with 0.36 mL physiological saline.
- Constant volume or concentration used: constant concentration.
- For solids, paste formed: yes: 1.0 grams test substance with 0.36 mL physiological saline.

Duration of exposure:

24 hours

Doses:

Males: 1600, 2000 and 2500 mg/kg
Females: 2000 mg/kg

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Observations: 10 and 30 minutes and 1, 2, 4 and 6 hours after application, and daily after removal of bandage up to 14 days after exposure.
Body weights: weekly
- Necropsy of survivors performed: yes

Statistics:

LD50 value was calculated using Probitanalysis.

Preliminary study:

Not applicable.

Sex:

male

Dose descriptor:

LD50

Effect level:

3 250 mg/kg bw

Based on:

test mat.

Sex:

female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Mortality:

Males:
1600 mg/kg: 0/5
2000 mg/kg: 2/5
2500 mg/kg: 1/5

Females:
2000 mg/kg: 0/5

Clinical signs:

other: Day of application: no clinical signs. Between Days 1 and 4 after application: hunched posture, subdued flanks, reduced activity, diarrhoea, uncoordinated movements, irregular breathing, rales Between Days 1-6 after application: Patchy erythema of treate

Gross pathology:

Non-surviving animals: pale spleen and liver, accentuated lobular pattern of the liver, and/or swollen urinary bladder.
Surviving animals: no abnormalities.

Other findings:

None.

Interpretation of results:

GHS criteria not met

Conclusions:

LD50 males: 3250 mg/kg
LD50 females >2000 mg/kg

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

3 250 mg/kg bw

Additional information

Toxicity (except dermal toxicity, irritation and corrosion) of SMCA (the sodium salt of MCAA) is identical to that of MCAA. Under physiological conditions both substances are completely ionised and the relevant moiety is the monochloroacetate ion. Dermal toxicity of SMCA is about tenfold lower than for MCAA (LD50: 3250 mg SMCA/kg bw in male rats and > 2000 mg/kg bw in female rats), presumably because the salt is much less absorbed through the skin than the acid.

Acute oral studies with MCA indicated a similar level of toxicity in all species. The key study (Hoechts 1979) has a Klimisch rating 2, was performed according to guideline but no GLP as GLP did not exist at that time. Acute dermal studies with MCA seem to indicate a much higher level of toxicity than for SMA (see above) but a similar level of toxicity across species; however, tests were not always performed in the same way and not according to the current test guideline. The dermal LD50 for MCA appears to be concentration dependent, i.e the LD50 is lower at higher concentrations. The key inhalation toxicity study (TNO, 2007, Klimisch 1, OECD guideline under GLP) indicates that the toxicity of MCA by inhalation is much lower than by the other two other routes.

When monochloroacetic acid is administered via inhalation, the organ first exposed is the lung. Besides the liver, the lung also expresses high levels of several biotransformation enzymes, which are also inducible in lung tissue (Elovaara et al., 2007). It could be discussed, because of the problems in measuring particle size in the key inhalation study (TNO, 2007), that the particle size may have been rather large (around 10 micron aerodynamic diameter), and that the particles may not have reached the lungs in sufficient amounts. However, with the expected particle size, the upper airways should at least have been reached, which was indeed confirmed by changes in breathing. Any other abnormalities such as nasal excretion or nasal encrustations were not seen, underlining the mildness of the effects at these concentrations.

Finally, it was checked in this study (TNO, 2007) whether, by dissolving MCA in water, possible complexes (glycolic acid) could have been formed in the test atmosphere which would explain the apparent lower toxicity when compared to the oral route. In the impingers, MCA was present at the expected levels, whereas glycolic acid or chlorine ions (Cl-) were not.

Assuming a minute ventilation of 0.8 L/kg for the rat, the rats inhaled approximately 200 L/kg in the 4-hour exposure period. Assuming also 100% absorption of monochloroacetic acid, the dose inhaled during 4 hours is 1268 x

0.2 mg/kg, which is approximately 250 mg/kg. LD50 values range from 55 -277.5 mg/kg. Apparently, in rats at the same total dose, the inhalatory route of exposure is less toxic than the oral route.

Hence, possible explanations for the finding that monochloroacetic acid does not cause any harmful effects in rats exposed up to 1268 mg/m3 during 4 hours while an equivalent oral dose at a single time point is lethal, include:

- the exposure to the compound is spread over 4 hours, thus preventing saturation of the metabolic system

- the compound may be (partly) metabolized by the lung tissue and therefore systemic exposure to the parent compound is lower, preventing toxic effects.

Justification for classification or non-classification

Based on the results of acute oral toxicity testing, SMCA should be classified as Toxic by the oral route (cat. 3).

Based on the results of the acute inhalation toxicity test with MCA and the acute dermal toxicity test with SMCA, SMCA should not be classified for acute toxicity by the inhalation and dermal route of exposure.