Reaction mass of calcium carbonate and calcium dihydroxide and silicon dioxide

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

5 mg/m³

DNEL related information

DNEL derivation method:

other: Derived from a OEL already calculated by the ACGIH

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

15 mg/m³

DNEL related information

DNEL derivation method:

other: Derived from a OEL already calculated by the SCOEL

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

hazard unknown (no further information necessary)

Acute/short term exposure

Hazard assessment conclusion:

hazard unknown (no further information necessary)

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

low hazard (no threshold derived)

Acute/short term exposure

Hazard assessment conclusion:

low hazard (no threshold derived)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

medium hazard (no threshold derived)

Additional information - workers

Acute/short-term exposure – systemic effects

Dermal DN(M)EL

No DNEL was derived because the potential effects are local. Based on its nature (mixture of insoluble and soluble inorganic solid compounds), transfer of the substance across the skin is considered insignificant.

 

Inhalation DN(M)EL

A possible acute effect associated with inhalation of the substance is related to its potential to increase the pH (increase of [OH-]). Because the systemic pH is efficiently regulated, and because the other relevant ion Ca2+ is physiologically important and thus also well regulated in the body, no systemic effects are to be expected under realistic acute exposure conditions

.

Acute/short-term exposure - local effects

Dermal DN(M)EL

Because the substance is considered to be irritating to the skin and corrosive to the eyes, no DNEL was calculated. Risk/exposure reduction measures are proposed based in a qualitative approach.

 

Inhalation DN(M)EL

The substance is classified as irritant to skin and respiratory tract. Because the Ca(OH)2 is the main constituent of the substance responsible for this effect, the short-term value STEL (15 min) of 4 mg/m3 respirable dust as recommended by the SCOEL (2008, reference (1)) was identified as a valid starting point. Assuming that 5% of the inhalable dust is respirable (see below), and that Ca(OH)2 can represent up to 87% of the substance, this would result in a acceptable concentration limit of 20 x 4 x 1.33 = 107 mg/m3 respirable dust.

A generally accepted approach to define a STEL or acute exposure limit is to multiply the 8h TWA using a factor defined by the quality/variability of the 8h-data set. The ACGIH states that “excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a work day, and under no circumstances should they exceed 5 times the TLV-TWA, provided that the TLV-TWA is not exceeded” . In order to define an inhalation DNEL for acute/short term exposure which is better in line with current practices and exposure limits, and which provides an additional margin of safety, a value of 3 times the inhalation DNEL for long-term exposure is proposed, i.e. 3 x 5= 15 mg/m3 inhalable dust.

 

Long-term exposure - systemic effects

Dermal DN(M)EL

No DNEL was derived because the potential effects are local. Based on its nature (mixture of insoluble and soluble inorganic solid compounds), transfer of the substance across the skin is considered insignificant.

 

Inhalation DN(M)EL

Considering the solubility of the different constituents of the substance, the bio-available components of the substance are mainlyand Ca2+ ions. Because the systemic pH is efficiently regulated, and because the Ca2+ ion is physiologically important and thus also well regulated in the body, no systemic effects are to be expected under realistic chronic exposure conditions.

 

Long-term exposure - local effects

Dermal DN(M)EL

Because the substance is considered to be irritating to the skin and corrosive to the eyes, no DNEL was calculated. Risk/exposure reduction measures are proposed based in a qualitative approach.

 

Inhalation DN(M)EL

The SCOEL (2008) proposed an 8h-TWA OEL value of 1 mg/m3 respirable dust for Ca(OH)2 and CaO. The 8h-TLV value for silicon dioxide is 0.025 mg/m3 respirable dust according to ACGIH® (2010, reference (2)), the TLV-basis being pulmonary fibrosis and lung cancer. This latter value is lower than the OELs currently defined in European countries (starting from 0.05 mg/m3). The particle size distribution of the dried substance was considered as a worst-case situation, i.e.the substance with “medium dustiness”characteristics. The results of the particle size analysis revealed a bimodal distribution. In order to estimate the amount of inhalable and respirable dust, the data was treated as two separate lognormal distributions as was suggested in the EPA’s Basic Concepts in Environmental Sciences, Module 3  (referece (3), see Figure 1). The distribution of the lower size particles (28% of the total population, median size: 97 µm) was analyzed separately in order to determine the inhalable and respirable fractions (see Figure 2).

The fraction of particles below 10µm, i.e. the respirable fraction, represented 2.9% of the particles smaller than 100 µm. An additional correction was performed to address the size selective sampling efficiency (reference (4), see Figure 3), leading to an estimated proportion of respiratory particles of 4.3% of the inhalable fraction.

  

The following elements were used in the rationale to obtain a conservative DNEL long-term exposure-local effects for the reaction mass of calcium carbonate, calcium dihydroxide and silicon dioxide:

• The 8h-TLV value as defined by ACGIH® for silicon dioxide, i.e. 0.025 mg/m3 respirable dust was used as the starting point for the definition of the DNEL long-term exposure –local effects. The use of an 8h-TLV as the starting point is an important element of the conservative character of the DNEL-definition.
• The level of silicon dioxide in the substance was set to 10%,. The choice that the typical value instead of the maximum value was used is considered justified for a DNEL for long-term exposure.
• The analysis of the particle size data as provided above shows that the assumption that 5% of the inhalable fraction is respirable is justified and conservative.

 

Using the above-mentioned elements, the following DNEL long-term exposure-local effects is obtained:

0.025 mg/m3 (8h-TLV for respirable dust) x 10 (silicon dioxide fraction) x 20 (respirable fraction) = 5 mg/m3 of inhalable dust of the reaction mass of calcium carbonate, calcium dihydroxide and silicon dioxide.

When comparing the proposed DNEL with the 8h-TWA value for Ca(OH)2 of 1 mg/m3 respirable dust as proposed by SCOEL and when taking the same conservative fraction for the respirable fraction, i.e., 5% of the inhalable fraction, and the typical content of Ca(OH)2 in the substance (40%), the resulting value of 50 mg/m³ is well above the proposed DNEL, showing that it also adequately addresses the hazards of Ca(OH)2.

References  

(1) Recommendation from the Scientific Committee on Occupational Exposure Limits for Calcium oxide (CaO) and Calcium Hydroxide (Ca(OH)2), European Commission, DG Employment, social Affairs and Equal Opportunities, SCOEL/SUM/137, February 2008

(2) Threshold Limit Values & Biological Exposure Indices for Chemical Substances and Physical Agents, ACGIH®, Signature Publications, 2010

(3) Basic Concepts in Environmental Sciences, Module 3: Characteristics of Particles, Size Distribution

http://www.epa.gov/eogapti1/bces/module3/distribu/distribu.htm, U.S. Environmental Protection Agency.

(4) American Conference of Governmental Industrial Hygienists : Particle Size-Selective Sampling for Particulate Air Contaminants. JH Vincent, Ed. ACGIH®

General Population - Hazard via inhalation route

Systemic effects

Acute/short term exposure

DNEL related information

Local effects

Acute/short term exposure

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Acute/short term exposure

DNEL related information

General Population - Hazard via oral route

Systemic effects

Acute/short term exposure

DNEL related information

Additional information - General Population

The foreseeable use of the reaction mass of calcium carbonate, calcium dihydroxide and silicon dioxide is restricted to industrial and professional use. Therefore no DNELs for the general population were defined. Nevertheless, DNELs for the general population are not expected requiring to be very different from those for workers considering the nature and the mode of action of the substance and its possible applications.