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Environmental fate & pathways

Hydrolysis

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Description of key information

In general, (abiotic) degradation is an irrelevant process for inorganic substances that are assessed on an elemental basis.

Key value for chemical safety assessment

Additional information

The data requirements with regard to hydrolysis can be considered to be fulfilled. According to the guidance, this endpoint is specifically needed for organic substances and less relevant for inorganic substances.

There are no studies available for “Reaction product of thermal process between 1000°C and 2000°C of mainly aluminium oxide and calcium oxide based raw materials with at least CaO+Al2O3 >80% , in which aluminium oxide and calcium oxide in varying amounts are combined in various proportions into a multiphase crystalline matrix”. As this substance is an UVCB substance with aluminium oxide (AL2O3) and calcium oxide (CaO) as main constituents, justification based on both main components were taken into account.    

 

Aluminium compounds:

Aluminium is the most abundant metal in the lithosphere, and is characterized by a complex biogeochemical cycle (Driscoll and Postek 1996; Exley, 2003). Aluminium can participate in hydrolysis reactions, thereby forming a number of monomeric and polymeric Al-hydroxides and this process is highly dependent on pH. Under REACH (ECHA 2008, Chapter R.7B – Endpoint Specific Guidance), the term ‘Hydrolysis’ refers to the “Decomposition or degradation of a chemical by reaction with water”, and this is a function of pH (i. e., abiotic degradation). Aluminium persists in the environment irrespective of whatever chemical species form as a result of hydrolysis, although it may form insoluble aluminium hydroxides that precipitate out of solution. Characterization of aluminium in environmental media is typically based on total aluminium concentrations inclusive of all specific chemical forms or species. Since hydrolysis changes the chemical form but does not decompose aluminium and since characterization of total aluminium considers all chemical forms, the concept of degradation of aluminium by hydrolysis is not relevant in the consideration of its environmental fate.

Calcium compounds:

When mixing calcium oxide with water, a proportion dissolves and dissociates, forming calcium ions (Ca2+) and hydroxyl ions (OH-). The release of hydroxyl ions causes a net pH increase. The rest of the substance remains in suspension. It can be reasonably assumed that in the aquatic environment the substance will normally be completely dissociated into its ions as the water solubility is relatively high compared to the environmental background concentration of calcium (i. e. 0.2-600 mg/L; median 40.2 mg/L; according to FOREGS Geochemical Baseline Mapping Programme) and due to dilution effects. Furthermore, the 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. As such, depending on the properties of the test medium, calcium oxide will be strongly neutralised in the initial period after application.

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