Reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide

Short-term toxicity to aquatic invertebrates

Description of key information

A reliable key study is available that assesses the short-term toxicity of the reaction mass of

calcium carbonate and calcium dihydroxide and calcium peroxide to aquatic invertebrates. The resulting 48h-EC50 is 6.8 mg/L.
From a supporting studies on hydrogen peroxide it can be concluded that the ecotoxicological effects observed for the reaction mass can be attributed to the adverse effects exerted by the hydrogen peroxide that is formed upon hydrolysis of the reaction mass.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

6.8 mg/L

Additional information

The short-term toxicity of the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide to aquatic invertebrates has been assessed in a recent GLP study according to OECD guideline 202 (Migchielsen, 2012).

In this key study, the daphnia were exposed to nominal concentrations of 1.0, 3.2, 10, 32 and 100 mg/L. The concentrations could not be verified by analyses based on calcium due to the high Ca background concentration of the test medium. Analyses based on hydrogen peroxide at the start of the test showed measured concentrations of 0.36, 1.1, 3.6, 11 and 22 mg/L. Nevertheless, the measured concentrations of hydrogen peroxide cannot be used for the derivation of the dose descriptors; this due to its instable nature. As a consequence, the nominal initial loading rates were used to calculate the NOEC and EC₅₀.

An 48h EC₅₀ of 6.8 mg/L and a NOEC of 3.2 mg/L was calculated.

 

Furthermore, supporting information is available on hydrogen peroxide (H₂O₂) and calcium dihydroxide (Ca(OH)₂), the primary hydrolytic degradation products of the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide.

 

For calcium dihydroxide, the short-term toxicity test with Daphnia magna (Egeler et al., 2007) was carried out according to the OECD 202 guideline taking into account GLP and thus resulting in a Klimish 1 score. The biological findings for Daphnia magna (immobility) were closely related to the initial pH of the test solutions, which ranged from 7.7 in the controls to 9.5, 9.7, 10.1, 10.7 and 11.1 at 14.8, 22.2, 33.3, 50 and 75 mg Ca(OH)₂/L, respectively. Therefore the initial pH is considered to be the main reason for the effects of calcium dihydroxide on Daphnia magna (Egeler et al., 2007). The 48h-EC₅₀ was found to be 49.1 mg/L under the conditions of this test.

 

The acute toxicity of hydrogen peroxide to invertebrates was tested in a 48h experiment with Daphnia pulex (Shurtleff, 1989). The test was performed in 1989 according to US EPA TSCA guidelines. The 48h-LC₅₀value determined from this study was 2.4 mg/L. As the 48h-LC₅₀ value for hydrogen peroxide is lower than the value found for calcium dihydroxide, the former was selected for the assessment of the reaction mass.

From this 48h-LC₅₀value a corresponding 48h-LC₅₀value can be calculated for the reaction mass, by taking into account the applicable chemical reaction (i.e. the amount of hydrogen peroxide formed is equimolar to the amount of calcium peroxide present in the reaction mass) and the composition of the reaction mass (i.e. the reaction mass contains ca. 75% calcium peroxide). Thus: 100 mg of the reaction mass contains 75 mg of calcium peroxide, which corresponds to 1.04 mmol of calcium peroxide. Therefore, 1.04 mmol (= 35.36 mg) of hydrogen peroxide is formed upon dissolution of 100 mg of calcium peroxide.

As a consequence, the 48h-LC₅₀ for the reaction mass, when calculated based on the 48h-LC₅₀ for hydrogen peroxide (2.4 mg/L) is:

           100 mg reaction mass                       yields             35.36 mg hydrogen peroxide

           6.79 mg reaction mass                      yields             2.4 mg hydrogen peroxide

           ==>      the 48h-LC₅₀ (reaction mass) = 6.8 mg/L

This calculated 48h-LC₅₀ value is the same as the value derived experimentally for the reaction mass, which demonstrates that the EC₅₀ value for the reaction mass can be predicted based on the toxicity of hydrogen peroxide.

 

It can thus be concluded that the ecotoxicological effects observed for the reaction mass can be attributed to the adverse effects exerted by the hydrogen peroxide that is formed upon hydrolysis of calcium peroxide.