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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, several relevant dose descriptors, both for the marine and fresh water environment, can be derived from reliable information that is available for hydrogen peroxide.
The fresh water 72h-EC50 for the reaction mass is 7.1 mg/L
The salt water 72h-EC50 for the reaction mass is 3.9 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
7.1 mg/L
EC50 for marine water algae:
3.9 mg/L
EC10 or NOEC for freshwater algae:
0.3 mg/L
EC10 or NOEC for marine water algae:
1.8 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 and cyanobacteria. Nevertheless, for this endpoint reliable informationis 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.

 

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.

 

Furthermore, a supporting study is available that examines the freshwater aquatic algae and cyanobacteria. It dates from 1991 and is performed according to the OECD 201 guideline (Walzer et al, 1991). In this static experiment, Chlorella vulgaris were exposed for 72 hours to nominal hydrogen peroxide concentrations of 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10 and 25 mg/L. The 72h-EC50 was found to be 2.5 mg/L and the 72h-NOEC value was 0.1 mg/L.

 

Both the marine and the freshwater dose descriptors can now be used as a starting point for the calculation of dose descriptors for the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide 

 

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

Fresh water

Analogously, the fresh water 72h-EC50 for the reaction mass can be calculated from the 72h-EC50 for hydrogen peroxide (2.5 mg/L):

           100 mg reaction mass                       yields             35.36 mg hydrogen peroxide

           7.07 mg reaction mass                      yields             2.5 mg hydrogen peroxide

           ==>      the FW 72h-EC50 (reaction mass) = 7.1 mg/L