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Ecotoxicological information

Short-term toxicity to fish

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Link to relevant study record(s)

Description of key information

Klimisch 1 study: 96h-LC50 = 50.6 mg/L for calcium dihydroxide and this for the freshwater fish rainbow trout (Egeler et al., 2007)
Klimisch 2 study: 96h-LC50 = 457 mg/L for calcium dihydroxide and this for the marine species Gasterosteus aculeatus (threespine stickleback) (Locke et al., 2009)
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

Fresh water fish

Fresh water fish
Effect concentration:
50.6 mg/L

Marine water fish

Marine water fish
Effect concentration:
457 mg/L

Additional information

The short-term toxicity study with the freshwater fish Oncorhynchus mykiss (rainbow trout) (Egeler et al., 2007) was executed according to OECD 203, resulting in a Klimisch 1 score. The biological findings (LC50 = 50.6 mg/L) were closely related to the initial pH of the test solutions. Therefore the initial high pH is considered to be the main reason for the effects of the test item on the fish.

The short-term toxicity study with the marine species Gasterosteus aculeatus Linnaeus (threespine stickleback) (Locke et al., 2009) was well described and a dose-response relationship was established (LC50 = 457 mg/L). However, the study was not carried out according to GLP, resulting in a Klimisch 2 score.