Calcium carbonate

Endpoint summary

Description of key information

Bulk calcium carbonate is an inorganic substance and does not undergo hydrolysis or biodegradation. In the environment, calcium carbonate will dissociate into calcium and carbonate ions.

Additional information

Calcium carbonate is an inorganic substance and therefore does not undergo hydrolysis or biodegradation. In the environment, calcium carbonate will dissociate into calcium and carbonate ions. These ions are naturally ubiquitous in the environment; calcium will be assimilated by species present in the water, soil or sediment and is necessary to maintain a good chemical balance in the environment and carbonate will become part of the carbon cycle.

Furthermore, calcium and carbonate ions are essential to all living organisms (flora and fauna) and their intracellular and extra-cellular concentrations are actively regulated. Therefore, bioaccumulation is not expected.

Studies in soil and sediment can not be performed due to the absence of an analytical test method that could distinguish between contributions to the analysed solution calcium concentration originating from the test material and that originating from the required soil/ sediment/ solution matrix. Even if the method guidelines were amended/deviated from and pure water was used as the aqueous phase for the soil/ sediment/ solution systems, a significant contribution of dissolved calcium would be expected in all samples due to the presence of calcium carbonate and other calcium salts as a naturally occurring mineral fraction in soils and sediments. Therefore, it would not be possible to distinguish between contributions to the analysed solution calcium concentration originating from the test material and that originating from the soils or sediments themselves.

Calcium carbonate presents only limited solubility in water and solubility characteristics are known to be sensitive to both solution pH and also the presence/partial pressure of carbon dioxide (which dissolves to give carbonate or bicarbonate ions). Therefore, changes with respect to aqueous phase pH and dissolved carbon dioxide concentrations on exposure to soils and sediments may lead to shifts in the relative solubility of the test material and potential precipitation and sedimentation on centrifugation of the samples; a process which can not be separated analytically from any true adsorption onto the soil or sediment phases.

The accumulation and mobility of calcium carbonate in soils has been documented in soil chemistry as the process of “calcification”. Calcification is the general process by which naturally occurring calcium carbonate or the product of dissolved calcium ions and either bicarbonate or carbonate ions (from dissolved carbon dioxide, the dominant form of the dissolved product being dependant on the solution pH) accumulates in soils. Most commonly, calcium carbonate accumulates in subsurface horizons of soils in subhumid, semiarid, or arid regions. Calcium carbonate has a propensity to leach through soil if water is applied, i.e. it does have some mobility through soil, providing sufficient water is present. As it moves downwards into layers where the water content is low, the leaching will stop. On this basis, calcium carbonate does not have a high potential for adsorption to soil. Likewise, the potential for adsorption of calcium carbonate to sediment is also expected to be low.