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Toxicity to microorganisms

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Description of key information

Klimisch 1 study (Egeler et al. (2007): activated sludge respiration inhibition test for Ca(OH)2 according to OECD 209; nominal EC50(3h) = 300.4 mg Ca(OH)2/L .
Rationale for read-across: in the environment, lime substances rapidly dissociate or react with water. These reactions, together with the equivalent amount of hydroxyl ions set free when considering 100mg of the lime compound (hypothetic example), are illustrated below:
Ca(OH)2 <-> Ca2+ + 2OH-
100 mg Ca(OH)2 or 1.35 mmol sets free 2.70 mmol OH-
CaO.MgO + 2H2O <-> Ca2+ + Mg2+ + 4OH-
100 mg CaO.MgO or 1.04 mmol sets free 4.15 mmol OH-
From these reactions it is clear that the effect of calcium magnesium oxide will be caused either by calcium ions, magnesium ions or hydroxyl ions. Since calcium and magnesium are abundantly present in the environment and since the effect concentrations are within the same order of magnitude of their natural concentrations, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions. Furthermore, the above mentioned calculations show that the base equivalents are within a factor 2 for calcium magnesium oxide and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of calcium magnesium oxide is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to calcium magnesium oxide is justified.

Key value for chemical safety assessment

EC50 for microorganisms:
300.4 mg/L

Additional information