Registration Dossier
Registration Dossier
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EC number: 215-138-9 | CAS number: 1305-78-8
Sediment toxicity
Administrative data
Link to relevant study record(s)
Description of key information
In accordance with column 2 of REACH Annex VII there is no need to consider testing, since CSA indicates no need to investigate further effects on sediment organisms.
Furthermore, the equilibrium partitioning method is not applicable to calcium oxide, since its effect is caused by the hydroxyl ions (pH effect). The fate and behaviour of these ions is determined by the pH buffer capacity of the sediment rather than a partitioning coefficient (Kd).
Because the sediment is expected to be more buffered than the water column, higher effect concentrations can be expected for sediment organisms.
Furthermore, the substance will be present in its dissociated form in the natural aquatic environment. The OH- ions will react with HCO3- to form water and carbonate ions which react with Ca2+ to form calcium carbonate. Calcium carbonate precipitates and deposits on the sediment. Calcium carbonate is a constituent of natural soils.
Key value for chemical safety assessment
Additional information
Calcium oxide first hydrolyses and then dissociates in the natural aquatic environment to forma Ca"+ and OH- ions. The OH- ions will react with HCO3- to form water and carbonate ions which react with Ca2+ to form calcium carbonate. Calcium carbonate precipitates and deposits on the sediment. Calcium carbonate and calcium and carbonate ions are ubiquitous in the environment and are found naturally in soil, water and sediment. Sediments naturally contain a high concentration of calcium and carbonate due to the physical and/or chemical weathering of calcium-rich rocks that takes place in the environment. The precipitation and deposition of calcium carbonate, usually as calcite, is a widely observed phenomenon in hard water lakes (Womble et al 1996). Calcium carbonate, usually derived primarily from autochthonous formation, has been reported to be a major component of the sediments of many hard water lakes. Calcium will be assimilated by species residing in the sediment and is necessary to maintain a good chemical balance in soils, water and sediment. The carbonate will become part of the carbon cycle and is then cycled throughout the biosphere.
Due to the natural occurrence of calcium carbonate in the environment, it is expected that calcium carbonate would not be toxic to sediment organisms and hence, long-term toxicity tests are scientifically unjustified.
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