Calcium carbonate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Bulk calcium carbonate and uncoated nano calcium carbonate are chemically identical. The only difference between them is the particle size, which may result in minor differences in physico-chemical properties. However, in biological systems and in the environment, both bulk and uncoated nano calcium carbonate are expected to have identical (eco)toxicological and environmental fate properties.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Uncoated nano calcium carbonate (Source): Refer to IUCLID section 1.2 for information on purity and impurities.
Bulk calcium carbonate (Target): Refer to IUCLID section 1.2 for information on purity and impurities.
The majority of new studies have been performed using uncoated nano calcium carbonate as the test material, hence it has been designated as the ‘Source’ in the read-across justification. However, for some endpoints data on bulk calcium carbonate are available and used to read-across to uncoated nano calcium carbonate so for these endpoints, marked with a * in the read-across justification document, bulk calcium carbonate is the ‘Source’.
3. ANALOGUE APPROACH JUSTIFICATION
Please refer to the justification attached in Section 13 of the dataset
4. DATA MATRIX
Please refer to the justification attached in Section 13 of the dataset

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.6800 (Modified Activated Sludge, Respiration Inhibition Test for Sparingly Soluble Chemicals)

Deviations:

no

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Description of key information

The toxicity of uncoated nano calcium carbonate to aquatic microorganisms has been investigated in a GLP study performed in accordance with OECD TG 209. The effect of uncoated nano calcium carbonate on the respiration of activated sewage sludge micro-organisms gave a 3 h EC50 of greater than 1000 mg/L.  The NOEC after 3 hours exposure was 1000 mg/L. The results of this study are read across to bulk calcium carbonate.

Additional information

No studies are available for bulk calcium carbonate. A study is available for uncoated nano calcium carbonate. This study, performed to OECD TG 209, assessed the toxicity of uncoated nano calcium carbonate to activated sewage sludge at nominal test concentrations of 10, 32, 100, 320 and 1000 mg/L (Youngs, 2010). No toxic effects were seen at any concentration of uncoated nano calcium carbonate tested. Hence, the 3 h EC50 was >1000 mg/L and the NOEC was 1000 mg/L. Uncoated nano calcium carbonate is therefore not toxic to aquatic microorganisms up to a concentration of 1000 mg/L. Evidence of undissolved test material was observed in some of the test vessels suggesting that the concentrations tested exceeded the maximum solubility of calcium carbonate in water.

The nano form of calcium carbonate was tested because this form was anticipated to represent the worst case as it is likely to be more soluble than the bulk form due to the smaller particle size and hence greater surface area. However, the results are directly applicable to the bulk form of calcium carbonate.