Dolomite (CaMg(CO3)2), calcined

Short-term toxicity to fish

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-
CaCO3.MgO + 2H2O <-> Ca2+ + Mg2+ + CO2 + 4OH-
100 mg CaCO3.MgO or 0.71 mmol sets free 2.86 mmol OH-
From these reactions it is clear that the effect of dolomite calcined 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 dolomite calcined and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of dolomite calcined is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to dolomite calcined 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 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.