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EC number: 908-749-3 | CAS number: -
Toxicity to aquatic algae and cyanobacteria
Administrative data
Link to relevant study record(s)
Description of key information
No experimental data are available that assess the toxicity of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium 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 magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide, and hence yields
a 72h-EC50 for the reaction mass of 6.17 mg/L and a 72h-NOEC of 2.81 mg/L.
Key value for chemical safety assessment
- EC50 for marine water algae:
- 6.17 mg/L
Additional information
No experimental data are available that assess the toxicity of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide to aquatic algae and cyanobacteria. Nevertheless, for this endpoint reliable information is available for hydrogen peroxide (H2O2) and magnesium hydroxide (Mg(OH)2), the primary hydrolytic degradation products of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide.
For magnesium hydroxide, the algal growth inhibition test (Migchielsen, 2010) was carried out according to GLP and to the OECD 201 guideline. In a 72-h static experiment, the test species (Pseudokircherella subcapitata) was exposed to nominal concentrations of 0, 0.10,1.0, 10 and 100 mg magnesium hydroxide /L. At 100 mg/L, the highest concentration tested, magnesium hydroxide was found to reduce the growth rate (-8.2%) and the yield (-31.7%) of the fresh water algae species. However, as a 50% effect level could not be reached, both the EC50 for growth rate reduction and the EC50 for yield inhibition are > 100 mg/L.
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 magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium 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 magnesium peroxide present in the reaction mass) and the composition of the reaction mass (i.e. the reaction mass contains ca. 37% magnesium peroxide).
Thus: 100 mg of the reaction mass contains 37 mg of magnesium peroxide, which corresponds to 0.66 mmol of magnesium peroxide. Therefore, 0.66 mmol (= 22.35 mg) of hydrogen peroxide is formed upon dissolution of 100 mg of the reaction mass.
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/L reaction mass yields 22.35 mg/L hydrogen peroxide
6.17 mg/L reaction mass yields 1.38 mg/L hydrogen peroxide
==> the 72h-EC50 (reaction mass) = 6.17 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/L reaction mass yields 22.35 mg/L hydrogen peroxide
11.2 mg/L reaction mass yields 2.5 mg/L hydrogen peroxide
==> the 72h-EC50 (reaction mass) = 11.2 mg/L
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