Aluminium metaphosphate

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Aluminium metaphosphate (CAS 13776-88-0) is poorly water soluble. The substance will be hydrolytically transformed into orthophosphate and aluminium ions in aqueous and biological systems. Aluminium is a naturally abundant element, the third most common element of the earth's crust. It is naturally released to the environment from the weathering of rocks and volcanic activity. Generally aluminium introduced in surface waters due to man-made applications cannot be distinguished from natural aluminium released during weathering of aluminium-bearing minerals.

The phosphate anions are ubiquitous in natural waters and essential micronutrient for many organisms. In acidic aquatic systems, aluminium exists in natural waters as a number of species, including dissolved and particulate forms. This again depends on many factors, especially pH, alkalinity, temperature, dissolved organic carbon, dissolved inorganic carbon and anion concentration. Furthermore, hydrolysis of aluminium ions has two possible “directions” towards a neutral pH, i.e. base hydrolysis and acid hydrolysis. Both acid and base hydrolysis of aluminium rapidly results in precipitation of aluminium hydroxide, which can become adsorbed on suspended particles or immobilised in sediment. A direct release of aluminium metaphosphate to terrestrial environment is negligible. If emitted to soil, depending on the buffer capacity of the soil, the substance will be neutralised and decomposes to aluminium hydroxide or oxide (gibbsite), that are stable and can become immobilised in soil. Nevertheless, as a result of this dynamic chemistry, the amount of aluminium associated with suspended particles is dependent on the chemical conditions. Factors that are known to affect aluminium speciation, such as pH and DOC, are also known to affect adsorption and desorption from particle surfaces. The adsorption potential of polyphosphates increases with increasing length of phosphate units i.e. the adsorption potential of triphosphate is higher compared to orthophosphate. Whereas the mobility and solubility in soil increases when the number of phosphate units is decreased, for example by hydrolysis of triphosphate to orthophosphate (Busman 1984). 

The air compartment is considered not relevant for aluminium metaphosphate (CAS 13776-88-0). Since these aluminium phosphates are usually not emitted to air, the amount of aluminium present in air that is related to the aluminium being considered here would be negligible compared with the amount coming from natural erosion of soil (Environment Canada Health Canada, 2000).

Reference:

Busman, Lowell Marion, (1984)

"Behavior of polyphosphates in soils " . Retrospective Theses and Dissertations. Paper 8979.

Canada. (2000). Canadian Environmental Protection Act: Persistence and Bioaccumulation Regulations, P.C. 2000-348, 23 March, 2000, SOR/2000-107, Canada Gazette. Part II, vol. 134, no. 7, p. 607−612. Available from: http://canadagazette.gc.ca/partII/2000/20000329/pdf/g2-13407.pdf