Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

This endpoint is specifically needed for organic substances and less relevant for inorganic substances. When mixing calcium oxide with water, the substance will be completely dissociated into its ions as the water solubility is relatively high compared to the environmental background concentration of calcium and due to dilution effects. Depending on the properties of the test medium, calcium oxide will be strongly neutralised in the initial period after application, by formation of calcium carbonate.

Data from Allan DJ (1995) indicate that most natural waters contain various bicarbonate and carbonate compounds, originating from dissolution of sedimentary rocks. Streamwater usually contains bicarbonates and carbonates and carbonic acid readily dissolves CaCO3 rocks, forming Ca(HCO3)2. The resulting streamwater is a solution of CO2, H2CO3, HCO3- and CO3^2- ions forming an effective buffer system that resists change in pH. The relative proportions of CO2, H2CO3, HCO3-and CO3^2- are pH dependent. At a pH below 4.5, only CO2 and H2CO3 are present and almost no HCO3- or CO3^2- is found. At higher pH values dissociation of H2CO3 occurs, HCO3-and CO3^2- are present and CO2 and H2CO3 are no longer detectable. At intermediate pH values, HCO3- predominates. Above a pH of about 8.3, HCO3- also declines with formation of CO3^2-. The dissociation dynamics are influenced by both temperature and ionic concentrations. Therefore, the chemistry of carbonate in water is clearly understood.