Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Aluminum 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. Aluminum present in surface waters due to man-made applications cannot be distinguished from natural aluminum released during weathering of aluminum-bearing minerals. The emission of the registered substance reaction mass of aluminium hydroxide and aluminium nitrate and aluminum sulphate is very low and mainly applies to (waste) water. If released into the environment, the substance will hydrolyse to aluminium hydroxide and precipitates in aquatic system or deposits as aluminium oxide in sediment or soil. Aluminum salts are used as coagulants and flocculants to cause fine materials that are suspended, soluble or both to agglomerate, for subsequent removal via sedimentation and filtration. As part of this agglomeration or coagulation process, most of the aluminum associated with the added aluminum salt hydrolyses to aluminum hydroxide, which precipitates and becomes part of the floc structure. As such, it makes up a part of the sludge generated by the treatment process. Sludge purged from clarifiers or accumulated in sedimentation basins of water treatment plants will not be released directly to the aquatic environment

A small amount of the aluminum added may stay with the finished water in either colloidal particulate (Al(OH)3) or soluble form (e.g., AlOH2+, Al(OH)2+, Al(OH)3, Al(OH)4-), dictated by the conditions of the treatment process and in particular, the pH.

 

The air compartment is considered not relevant for reaction mass of aluminium hydroxide and aluminium nitrate and aluminium sulphate. Since these aluminum salts are usually not emitted to air, the amount of aluminum present in air that is related to the aluminum salts being considered here would be negligible compared with the amount coming from natural erosion of soil (Environment Canada Health Canada, 2000)

 

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.

 

As mentioned above, a direct release of reaction mass of aluminium hydroxide and aluminium nitarte and aluminium sulphate to terrestrial environment is negligible. If emitted to soil, depending on the buffer capacity of the soil, reaction mass of aluminate sulfate and aluminium nitrate will be neutralised and decomposes to aluminium hydroxide or oxide (gibbsite), which are stable and can become immobilised in soil. Nevertheless, the fate of aluminium in the terrestrial environment will also depend on local conditions.