Calcium acetylide

Specific investigations: other studies

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

specific investigations: other studies

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

Details on results:

There was no difference in the lung function parameters (FVC, FEV1, peak flow (PF), forced expiratory flow after exhalation of 50% and 75% of the vital capacity (FEF50 and FEF75)), adjusted for age, sex, race, height and smoking. However, the dust caused an acute decrease in PF with increasing exposure level; the decrease was 1-2% per mg/m3 of respirable dust.

Conclusions:

In a cross-sectional study in 16 Portland cement manufacturing plants in the US, respiratory symptoms and lung function parameters were compared in 2736 cement workers and 755 controls, exposed to 0.57 (0.01-46) mg/m3 (respirable dust) and 2.9 (0.01-79) mg/m3 (total dust). There was no difference in the lung function parameters.

Executive summary:

In a cross-sectional study in 16 Portland cement manufacturing plants in the US, respiratory symptoms and lung function parameters were compared in 2736 cement workers and 755 controls, exposed to 0.57 (0.01-46) mg/m3 (respirable dust) and 2.9 (0.01-79) mg/m3 (total dust). There was no difference in the lung function parameters (FVC, FEV1, peak flow (PF), forced expiratory flow after exhalation of 50% and 75% of the vital capacity (FEF50 and FEF75)), adjusted for age, sex, race, height and smoking. However, the dust caused an acute decrease in PF with increasing exposure level; the decrease was 1-2% per mg/m3 of respirable dust.

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:

specific investigations: other studies

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

Details on results:

The SCOEL concludes on an OEL of 1 mg/m3 of respirable dust and a STEL of 4 mg/m3 for calcium oxide and calcium hydroxide.

Conclusions:

The SCOEL concludes on an OEL of 1 mg/m3 of respirable dust and a STEL of 4 mg/m3 for calcium oxide and calcium hydroxide.

Executive summary:

The SCOEL concludes on an OEL of 1 mg/m3 of respirable dust and a STEL of 4 mg/m3 for calcium oxide and calcium hydroxide.

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 3

Endpoint:

specific investigations: other studies

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

Details on results:

No effects in lung function parameters, nasal peak expiratory flow or in eosinophilic cationic protein, myeloperoxidase and hyaluronic acid in the nasal lavage fluid, has been observed at 1.2 mg/m3 total dust (range: 0.4-5.8 mg/m3). In contrast, the nasal mucociliary clearance was significantly longer (mean and range: 13.4 min and 6.0-26 min) in the exposed group compared to the controls (10.0 min and 4-20 min), determined by the saccharin test. This effect is most probably a result of the different in temperature (42 to 28°C).

Fifteen Finnish pulp-mill workers were compared with 15 matched unexposed referents from the transportation and office departments. The mean total dust level among the kiln workers was 1.2 mg/m3 (range: 0.4-5.8 mg/m3) and the temperature was 42°C. There was no statistically significant difference in self-reported symptoms, nasal bleeding, crusts in the nose, nasal blockage and nasal secretion. Neither did the clinical examination reveal statistically significant more inflammation in the nose and throat among the exposed workers, nor was any statistically significant difference observed in lung function parameters, nasal peak expiratory flow or in eosinophilic cationic protein, myeloperoxidase and hyaluronic acid in the nasal lavage fluid. In contrast, the nasal mucociliary clearance was significantly longer (mean and range: 13.4 min and 6.0-26 min) in the exposed group compared to the controls (10.0 min and 4-20 min), determined by the saccharin test. After rebuilding the kiln, the mean total dust level was reduced to 0.2 mg/m3 (range: 0.1-0.6 mg/m3) and the temperature to 28°C. The mean saccharin transition time normalized in the exposed workers (8.6 min and 1.4-15 min) and it was no longer different from the mean value in the controls (10.2 min and 5.5-20 min). The authors interpreted the normalization to be due to the decrease in the lime dust level, but mentioned that some influence of reduced temperature cannot be excluded. Overall, the NOAEL for all effects, except the nasal mucociliary clearance, is 1.2 mg/m3 total dust.

Conclusions:

No effects in lung function parameters, nasal peak expiratory flow or in eosinophilic cationic protein, myeloperoxidase and hyaluronic acid in the nasal lavage fluid, has been observed at 1.2 mg/m3 total dust (range: 0.4-5.8 mg/m3).

Executive summary:

No effects in lung function parameters, nasal peak expiratory flow or in eosinophilic cationic protein, myeloperoxidase and hyaluronic acid in the nasal lavage fluid, has been observed at 1.2 mg/m3 total dust (range: 0.4-5.8 mg/m3). In contrast, the nasal mucociliary clearance was significantly longer (mean and range: 13.4 min and 6.0-26 min) in the exposed group compared to the controls (10.0 min and 4-20 min), determined by the saccharin test. This effect is most probably a result of the different in temperature (42 to 28°C).

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.

Description of key information

Adverse effects of CaC2 are considered to be limited to local reactions. Systemic effects from exposure to the breakdown products are not expected: Decomposition of CaC2 leads to Ca(OH)2 and C2H2. Compared to a daily intake level of 2,500 mg/kg/d (EFSA, 2012) resorption of calcium ions from dissociated Ca(OH)2 (inhaled CaC2 particles) is considered to be negligible. The second decomposition product, C2H2, is a gas and therefore expected to be exhaled. 
At low-level exposures, sensory irritation and a decrease of the lung function parameters at long-term exposures are considered to be the critical effects. Sensory irritation is expected to be prevented by 1mg/m³ respirable CaO dust (Cain et al., 2004). No relevant respiratory effect was found at an exposure level of 1 mg/m³ (range: 0.4-5.8 mg/m³) of total lime dust (Torén et al. 1996). A limit of 1 mg/m³ is protective against long-term exposure to Ca(OH)2, as furthermore supported by studies on cement dust exposures that has a similar alkalinity compared to CaC2 in aqueous solution (SCOEL, 2008). It should be emphazised that this value is conservative as the effects reported by Cain et al. (2004) are based on sensory irritation but not on lung function parameters.

Additional information

In aqueous solution, calcium carbide (CaC2) rapidly decomposes into calcium hydroxide (Ca(OH)2) and acetylene (C2H2). For local effects in the lung the main effects are related to calcium hydroxide, which liberates OH- ions, affecting the skin and the mucous membranes.

Potential respiratory irritation of calcium hydroxide and calcium oxide has been assessed in several epidemiological studies and studies in volunteers. The systemic effects of CaC2 is considered to be negligible at normal occupational exposures. The fraction of calcium in CaC2 is 63 % (w/w). Assuming an exposure level of 1 mg/m³ and an air volume of 10 m³ inhaled during an 8-hour workday, this results in an inhaled dose of 6.3 mg calcium per day. Thus, occupational exposures makes negligible contribution to the daily systemic calcium uptake as the Tolerable Upper Intake Level for calcium is 2500 mg/day (EFSA Journal 2012;10(7): 2814).

Key studies for the assessment of respiratory irritation are Cain et al. (2004, 2008), Toren et al. (1996), Abrons et al. (1988). Several other studies on occupational exposure to limestone, Portland cement and various sources of CaO and Ca(OH)2 have been summarized by the Scientific Committee on Occupational Exposure Limits (SCOEL) in 2008.

In Torén et al. (1996), 15 Finnish pulp-mill workers were compared with 15 matched unexposed referents from the transportation and office departments. The mean total lime dust level was 1.2 mg/m³ (range: 0.4-5.8 mg/m³) and the temperature was 42 °C. No effects on lung function parameters, nasal peak expiratory flow or in eosinophilic cationic protein, myeloperoxidase and hyaluronic acid in the nasal lavage fluid have been observed at 1.2 mg/m³ total dust (range: 0.4-5.8 mg/m³). In contrast, the nasal mucociliary clearance was significantly longer (mean and range: 13.4 min and 6.0-26 min) in the exposed group compared to the controls (10.0 min and 4-20 min), determined by the saccharin test. This effect is most probably a result of the difference in temperature (42 to 28 °C). Overall, the NOAEL for all effects, except the nasal mucociliary clearance, is 1.2 mg/m³ total dust.

Abrons et al. reported on a cross-sectional study in 16 Portland cement manufacturing plants in the US. Respiratory symptoms and lung function parameters were compared in 2736 cement workers and 755 controls, exposed to 0.57 (0.01-46) mg/m³ (respirable dust) and 2.9 (0.01-79) mg/m³ (total dust). There was no difference in lung function parameters.

Cain et al. (2004) exposed 12 lightly exercising volunteers (breathing through the nose) for 20 min to 1 to 5 mg/m³ CaO. Nasal resistance, nasal secretion, mucociliary transport time, and chemaesthetic magnitude (for example, irritation, pungency, piquancy, cooling and burning), were assessed. The mass median aerodynamic diameter was 6.53±0.76 µm. The CaO exposures caused a steady increase in irritation during the 20 min period and no steady state level was reached. In the nose, 1 and 2 mg/m³ gave rise to an equivalent effect at the end of the exposure, which corresponded to the irritation effect of about 15 % CO2. The 5 mg/m³ level had an effect equivalent to 20 % CO2. The values were significantly above the background. No significant effect occurred in nasal secretion and mucociliary clearance, determined by the saccharin test. The study interpreted the effects as “very few people used the term irritation to describe the nasal sensation evoked by 10 % CO2. Some would use that term at 15 % CO2 and the majority would use it at 20 % CO2” and also the authors conclude “that the psychophysical judgements produced results consistent with the

known effect that calcium oxide would evoke irritating chemesthesis at exposures in the range of 2 to 5 mg/m³”. It was concluded that the effects of CaO, which were not dose dependent in the range from 1 to 2 mg/m³, were of no adverse health significance. The effect had not reached the maximum within the 20 min of exposure although the effect was levelling off. Taking these two facts into account, an exposure limit of 1 mg/m³ is deemed to protect against adverse sensory irritation.

Cain et al. (2008) investigated the airway effects of 2.5 mg/m³ CaO in 6 male and 6 female volunteers, aged 18-35 years, who were exposed for 45 min. The mass mean aerodynamic diameter was 6.5 μm and the geometric standard deviation 2.6. The sensory effects were highest in the nose, lower in the throat and lowest in the eyes. The maximum effect was reached about 30 min after the initiation of the exposure, followed by adaptation.

The authors interpreted their results as “people would agree that feel in the nose becomes irritating at about 17-18 % carbon dioxide”. Thus, the 2.5 mg/m³ level can be considered at the LOAEL. Overall, considering the effect at the 2.5 mg/m³ level, the limited number of subjects in the study and sensory irritation increasing as a monotonic function, this suggests that an OEL of 1 mg/m³ can be derived from this study which is in agreement with the results from Cain et al. (2004).