Calcium acetylide

Endpoint summary

Description of key information

In aqueous solution, calcium carbide (CaC2) rapidly decomposes into calcium hydroxide (Ca(OH)2) and

acetylene (C2H2). Acute toxicity studies on the decomposition products are available: Oral (OECD 425) and dermal (OECD 402) toxicity studies on Ca(OH)2; and acute inhalation toxicity studies on C2H2.

An additional acute oral toxicity study was disregarded due to major deficiencies in methodology and documentation.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: oral

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

As calcium carbide instantly hydrolyses to Ca(OH)2 and C2H2 upon contact with water/moisture the assessment is based on the degradation products. For details please refer to the read across report in section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Sex:

female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Mortality:

No deaths occured during the study.

Clinical signs:

other: Slightly ruffled fur was noted at the 30-minutes reading up to day 2, 4, 5 or 7 in four animals. Hunched posture was observed at the 30-minutes reading up to the 1-, 3- or 5-hour reading in these animals. Slightly to moderately ruffled fur at the 30-minut

Gross pathology:

No macroscopic findings were observed at necropsy.

Interpretation of results:

GHS criteria not met

Conclusions:

The median lethal dose for the test item Precal 50S (Calcium dihydroxide (hydrated lime)) after single oral administration to female rats, observed over a period of 14 days is: LD50 (rat): greater than 2000 mg/kg body weight.
According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item is not classified.

Executive summary:

In an acute oral toxicity study performed according to OECD TG 425, groups of 5 fasted female Wistar rats were given a single oral dose of Calcium hydroxide (98.2%) in polyethylene glycol at a dose of 2000 mg/kg bw and were observed for 14 days.

No cases of mortality were observed. There were no treatment related necropsy findings. A slight decrease in body weight between the day of dosing and day 8 was observed in one animal treated with the test item. This was an isolated and transient change and the animal recovered until the end of the observation period.

Clinical signs included slightly ruffled fur noted at the 30-minutes reading up to day 2, 4, 5 or 7 in four animals. Hunched posture was observed at the 30-minutes reading up to the 1-, 3- or 5-hour reading in these animals. Slightly to moderately ruffled fur at the 30-minutes reading up to day 13, hunched posture at the 30-minutes reading up to day 7, slight sedation at the 1-hour observation up to day 6 as well as deep respiration up to day 11 and rales at the 30-minutes observation up to day 2 were noted in the fifth animal. Clinical signs were shown to be reversible until scheduled sacrifice on day 15.

Based on these results, the LD50 for the test item after single oral administration to female rats, is greater than 2000 mg/kg body weight.

According to EC Regulation No. 1272/2008 and subsequent regulations, the test item is not classified.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Reference 2

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

disregarded due to major methodological deficiencies

Study period:

2019

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Justification for type of information:

The present study shows major deficiencies in method and documentation. First of all, the report does not state sufficient details for gavage administration, including vehicle and the form, in which calcium acetylide was applied. In case of calcium acetylide, this however is important as the substance reacts violently with water to generate gaseous acetylene and calcium hydroxide, thereby leading to a local depletion of water. The reaction is exothermic and can locally create excess heat, which can potentially lead to local burns and tissue damage. Second, the test material specifications regarding the purity of the applied calcium acetylide and the content of potential impurities, was not specified. It is mentioned in the report that calcium acetylide often contains impurities including arsenic and phosphorous, which themselves can exert toxic effects potentially covering those of the test substance.
In addition, the number of animals which suffered from mortality and their individual symptoms are not reported. The general clinical signs which were reported in response to calcium acetylide treatment included dryness of mouth (tongue was retracted) and bleeding from the mouth. These signs (especially bleeding from mouth) indicate that local effects could be involved in the observed mortality after oral administration of calcium acetylide. Therefore, there is substantial doubt from the study design and reporting that systemic availability and a specific systemic mode of action of the substance are responsible for intoxication, eventually leading to the observed mortality.
Based on the deficiencies described, evaluation of the inherent quality of the provided data with the ECVAM ToxRTool resulted in the assignment of Klimisch category 3 and thus the study was not regarded suitable for the assessment of acute toxicity of the test substance calcium acetylide.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 420 (Acute Oral Toxicity - Fixed Dose Method)

Deviations:

yes

Remarks:

only two fixed dose levels were administrated

GLP compliance:

not specified

Test type:

fixed dose procedure

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male

Route of administration:

oral: gavage

Vehicle:

not specified

Doses:

2g/kg
5g/kg

No. of animals per sex per dose:

6

Control animals:

yes

Key result

Sex:

male

Dose descriptor:

LD50

Effect level:

ca. 2 000 mg/kg bw

Based on:

test mat.

Mortality:

yes at 5g/kg

Clinical signs:

other: rolling of the tail, restlessness, dryness of mouth (tongue was retracted), bleeding from the mouth, and brushing their head with the husk inside the cage

Interpretation of results:

study cannot be used for classification

Conclusions:

In an acute oral toxicity study performed according to OECD TG 420, male Wistar rats were given calcium acetylide as a single oral dose of 2000 and 5000 mg/kg bw and observed for 14 days. At 5000 and 2000 mg/kg bw, 85% and 50% of animals were found dead, respectively, within the observation period. However, the study was disregarded due to major deficiencies in study design and documentation.

Executive summary:

In an acute oral toxicity study conducted according to OECD TG 420, groups of six male Wistar rats per dose were given a single oral dose of calcium acetylide at doses of 2000 and 5000 mg/kg bw and observed for 14 days. At 5000 and 2000 mg/kg bw, 85% and 50% of animals were found dead, respectively, within the observation period. Clinical signs included rolling of the tail, restlessness, dryness of mouth (tongue was retracted), bleeding from the mouth, and brushing their head with the husk inside the cage. Based on these results, the LD50 for male rats is considered to be 2000 mg/kg bw.

The present study was disregarded due to major deficiencies in method and documentation.

First of all, the report does not state sufficient details for gavage administration, including vehicle and the form, in which calcium acetylide was applied. In case of calcium acetylide, this however is important as the substance reacts violently with water to generate gaseous acetylene and calcium hydroxide, thereby leading to a local depletion of water. The reaction is exothermic and can locally create excess heat, which can potentially lead to local burns and tissue damage. Second, the test material specifications regarding the purity of the applied calcium acetylide and the content of potential impurities, was not specified. It is mentioned in the report that calcium acetylide often contains impurities including arsenic and phosphorous, which themselves can exert toxic effects potentially covering those of the test substance.

In addition, the number of animals which suffered from mortality and their individual symptoms are not reported. The general clinical signs which were reported in response to calcium acetylide treatment included dryness of mouth (tongue was retracted) and bleeding from the mouth. These signs (especially bleeding from mouth) indicate that local effects could be involved in the observed mortality after oral administration of calcium acetylide. Therefore, there is substantial doubt from the study design and reporting that systemic availability and a specific systemic mode of action of the substance are responsible for intoxication, eventually leading to the observed mortality.

Based on the deficiencies described, evaluation of the inherent quality of the provided data with the ECVAM ToxRTool resulted in the assignment of Klimisch category 3 and thus the study was not regarded suitable for the assessment of acute toxicity of the test substance calcium acetylide and will not be used for classification of the substance.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

As calcium carbide instantly hydrolyses to Ca(OH)2 and C2H2 upon contact with water/moisture the assessment is based on the degradation products. For details please refer to the read across report in section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Sex:

male

Dose descriptor:

LC0

Effect level:

160 500 mg/m³ air (nominal)

Based on:

test mat.

Exp. duration:

4 h

Mortality:

no mortality

Interpretation of results:

GHS criteria not met

Conclusions:

Acute inhalation exposure of male Sprague Dawley rats to 10-15% v/v acetylene (equivalent to 107,000 - 160,500 mg/m3) for 4 hours did not result in mortality.

Executive summary:

In an acute inhalation toxicity study, groups of male Sprague Dawley rats were exposed by inhalation route to acetylene in air for 4 hours to whole body at concentrations of 10-15% (v/v) acetylene in air (equivalent to 107,000 - 160,500 mg/m³).

There was no mortality observed after 4 hours exposure.

Based on these results, GHS criteria are not met and no classification according to Regulation (EC) No. 1272/2008 is warranted.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Reference 2

Endpoint:

acute toxicity: inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

As calcium carbide instantly hydrolyses to Ca(OH)2 and C2H2 upon contact with water/moisture the assessment is based on the degradation products. For details please refer to the read across report in section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Sex:

not specified

Dose descriptor:

LC0

Effect level:

25 000 ppm

Based on:

test mat.

Exp. duration:

1 h

In humans, acetylene is not acutely toxic below its lower explosive limit of 2.5% (25,000 ppm). Inhalation of 10% acetylene (100,000 ppm) for 1 hour does not cause acute toxicity. Inhalation of 33% or 35% has caused unconsciousness within 7 and 5 minutes, respectively.

Interpretation of results:

GHS criteria not met

Conclusions:

In humans, acetylene is not acutely toxic below its lower explosive limit of 2.5% (25,000 ppm). Inhalation of 10% acetylene (100,000 ppm) for 1 hour does not cause acute toxicity. Inhalation of 33% or 35% has caused unconsciousness within 7 and 5 minutes, respectively

Executive summary:

In an acute inhalation toxicity study in humans, acetylene is not acutely toxic below its lower explosive limit of 2.5% (25,000 ppm). Inhalation of 10% acetylene (100,000 ppm) for 1 hour does not cause acute toxicity. Inhalation of 33% or 35% has caused unconsciousness within 7 and 5 minutes, respectively.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

As calcium carbide instantly hydrolyses to Ca(OH)2 and C2H2 upon contact with water/moisture the assessment is based on the degradation products. For details please refer to the read across report in section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 500 mg/kg bw

Based on:

test mat.

Mortality:

There were no indications of toxic effects from the test sample after dermal application.

Clinical signs:

other: Overall, redness, followed by scabbing, did occur in the area of the treated skin after the dressing was removed and the skin was cleaned. Slight redness after removal of the dressing was observed in one female rabbit. Moderate redness plus scabbing was o

Gross pathology:

Dissection of the rabbits yielded no particular results.

Other findings:

- Histopathology: The pathological-histological examination of the liver, kidneys, lung and skin yielded no particular results.

Interpretation of results:

GHS criteria not met

Conclusions:

The available data showed that the tested White lime paste caused no acute toxic effect after dermal application. However, the test did show skin irritating effects from the test sample.
According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item is not classified.

Executive summary:

In an acute dermal toxicity study according to OECD TG 402, groups of 5 New Zealand White rabbits/sex were dermally exposed to Calcium hydroxide in water (White lime paste) for 24 hours to 100 cm²of shorn skin at a dose of 2500 mg/kg. Animals were then observed for 14 days.

There were no treatment related deaths or necropsy signs. Clinical signs included redness, followed by scabbing, occuring in the area of the treated skin after the dressing was removed and the skin was cleaned. Slight redness after removal of the dressing was observed in one female rabbit.

Moderate redness plus scabbing was observed after removal of the dressing in four females rabbits and three male rabbits. Moderate redness plus pronounced scabbing was observed after removal of the dressing in one male rabbit. The pathological-histological examination of the liver, kidneys, lung and skin yielded no particular results.

Based on these results, GHS criteria are not met and classification is not warranted according to Regulation (EC) No. 1272/2008.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Additional information

In aqueous solution, calcium carbide (CaC2) rapidly decomposes into calcium hydroxide (Ca(OH)2) and acetylene (C2H2). Calcium hydroxide releases calcium and hydroxyl ions. Hydroxyl ions can cause local effects, calcium ions are resorbed in the intestine. C2H2 is released as a gas and is not expected to contribute to any oral or dermal effects.

Acute oral toxicity of Ca(OH)2 was tested in rats (Arcelin, 2007). No mortality occurred up to the limit dose of 2000 mg/kg. Acute dermal toxicity of Ca(OH)2 was tested in rabbits (Kietzmann, 1994). The test did revealed skin irritating effects caused by the test material, but no mortality occurred at 2500 mg/kg.

From these results it can be concluded that CaC2 is not acutely toxic.

Since decades of production and use, the acute toxicity of acetylene is well understood to be that of a simple asphyxiant. In humans, acetylene is not acutely toxic below its lower explosive limit of 2.5% (25,000 ppm). Inhalation of 10% acetylene (100,000 ppm) for 1 hour does not cause acute toxicity. Inhalation of 33% or 35% has caused unconsciousness within 7 and 5 minutes, respectively (Davidson, 1925).

Justification for selection of acute toxicity – oral endpoint
OECD guideline study with Ca(OH)2

Justification for selection of acute toxicity – inhalation endpoint
Non-GLP, non-guideline study with C2H2

Justification for selection of acute toxicity – dermal endpoint
OECD Guideline study with Ca(OH)2

Justification for classification or non-classification

Available data suggest lack of acute toxicity of calcium carbide, based on the assessment of the decomposition products calcium hydroxide and acetylene.