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Toxicity to aquatic algae and cyanobacteria

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Description of key information

No experimental data are available that assess the toxicity of the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide to aquatic algae and cyanobacteria. Nevertheless, a relevant dose descriptor can be derived from the most reliable information that is available for hydrogen peroxide. For hydrogen peroxide the marine water 72h-EC50 is 1.38 mg/L and the 72h-NOEC is 0.63 mg/L.

These values can be recalculated based on the amount of H2O2 that can be formed from the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide and hence yields an EC50 of 3.9 mg/L and a NOEC of 1.78 mg/L for the reaction mass.


Key value for chemical safety assessment

EC50 for marine water algae:
3.9 mg/L
EC10 or NOEC for marine water algae:
1.78 mg/L

Additional information

No experimental data are available that assess the toxicity of the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide to aquatic algae. Nevertheless, for this endpoint reliable information is available for 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. Furthermore, a supporting study is available on the toxicity of calcium peroxide on cyanobacteria, in which a LOEC is determined based on the PSII efficiency. However, as PSII efficiency is an indirect parameter related to the photosynthesis process, this LOEC is not comparable to the dose descriptors determined in the OECD 201 studies.

 

For calcium dihydroxide, the algal growth inhibition test (Egeler, 2007) was carried out according to GLP and to the OECD 201 guideline. In a 72-h static experiment, the test species (Pseudokirchnerella subcapitata) was exposed to nominal concentrations of 0, 48, 80, 138, 235 and 400 mg calcium dihydroxide/L.

The inital pH of the test vessels was 5.8 for the control and 6.4, 6.8, 7.2, 8.1 and 11.4, respectively for the solutions containing increasing amounts of test material. A clear concentration-response relationship was observed and a 72h-EC50 of 184.57 mg/L and a 72h-NOEC of 48 mg/L were established.

The pH of the medium at concentrations resulting in a considerable growth inhibition, was below 8 and the biological findings are therefore not attributed to the initial pH of the test solutions. It was however observed that with increasing test item concentrations precipitates were formed over time to which algae adhered, leading to their flocculation. This can be explained since the test item is known to react with CO2 to calcium carbonate, which is poorly soluble in water leading to the formation of precipitates. The flocculation of algae is thus considered to be the predominant biologically relevant effect in this system test.

 

The key study assessing the toxicity of hydrogen peroxide to aquatic algae and cyanobacteria as identified in the REACH registration dossier for hydrogen peroxide is performed on a salt water species, namely Skeletonema costatum. In this study (Knight et al, 1997), the test organisms were exposed to nominal concentrations of 0, 0.625, 1.25, 2.5, 5 and 10 ppm of hydrogen peroxide for 72 hours. The 72h-EC50 and 72h-NOEC values were 1.38 mg/L and 0.63 mg/L, respectively.

 

From the 72h-EC50 value for hydrogen peroxide, a corresponding 72h-EC50 value 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.

Marine

As a consequence, the marine 72h-EC50 for the reaction mass can be calculated from the 72h-EC50 for hydrogen peroxide (1.38 mg/L):

           100 mg reaction mass                       yields             35.36 mg hydrogen peroxide

           3.90 mg reaction mass                      yields             1.38 mg hydrogen peroxide

           ==>      the MW 72h-EC50 (reaction mass) = 3.9 mg/L

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