Dolomite (CaMg(CO3)2), calcined

Short-term toxicity to aquatic invertebrates

Description of key information

Klimisch 1 study: nominal 48h-EC50 value for the immobility of Daphnia magna = 49.1 mg Ca(OH)2 /L (Egeler et al., 2007)
Klimish 2 study: 96h-LC50 for marine water crustacean Crangon septemspinosa Say = 158 mg Ca(OH)2 /L (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 invertebrates

Fresh water invertebrates

Effect concentration:

49.1 mg/L

Marine water invertebrates

Marine water invertebrates

Effect concentration:

158 mg/L

Additional information

The short-term toxicity test with Daphnia magna (k_Egeler et al., 2007) was carried out according to the OECD 202 guidance taking into account GLP and thus resulting in a Klimish 1 score. The biological findings for Daphnia magna (immobility) were closely related to the initial pH of the test solutions, which ranged from 7.7 in the controls to 9.5, 9.7, 10.1, 10.7 and 11.1 at 14.8, 22.2, 33.3, 50 and 75 mg Ca(OH)2 /L, respectively. Therefore the initial pH is considered to be the main reason for the effects of calcium dihydroxide on Daphnia magna (Egeler et al., 2007).

The short-term toxicity test with the marine species Crangon septemspinosa Say (Locke et al., 2009) was conducted by a standard methodology developed by the laboratory. Test conditions are well described, a dose-response relationship was established (96h-LC50 = 158 mg/L); no statistics were reported. This resulted in a Klimish 2 score.