Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

The registered substance is used as coagulants and flocculants to cause fine materials that are suspended, soluble or both to agglomerate, for subsequent removal via sedimentation and filtration and the releases of aluminum to the environment from the commercial applications are expected to be very small.

Aluminium is the most abundant metallic element and constitutes about 8% of the Earth’s crust. Aluminium salts like the registered substance are widely used in water treatment as coagulants to reduce organic matter, colour, turbidity and microorganism levels. Such use may lead to increased concentrations of aluminium in finished water. Where residual concentrations are high, undesirable colour and turbidity may ensue. Concentrations of aluminium at which such problems may occur are highly dependent on a number of water quality parameters and operational factors at the water treatment plant. Aluminium intake from foods, particularly those containing aluminium compounds used as food additives, represents the major route of aluminium exposure for the general public. The contribution of drinking-water to the total oral exposure to aluminium is usually less than 5% of the total intake ((WHO (2010), Aluminium in drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality. Geneva, World Health Organization (WHO/HSE/WSH/10.01/13)).

 

Aluminium is released to the environment mainly by natural processes. Several factors influence aluminium mobility and subsequent transport within the environment. These include chemical speciation, hydrological flow paths, soil–water interactions and the composition of the underlying geological materials. Acid environments caused by acid mine drainage or acid rain can cause an increase in the dissolved aluminium content of the surrounding waters (WHO, 1997; ATSDR, 2008).

 

Aluminium can occur in a number of different forms in water. It can form monomeric and polymeric hydroxy species, colloidal polymeric solutions and gels, and precipitates, all based on aquated positive ions or hydroxylated aluminates. In addition, it can form complexes with various organic compounds (e.g. humic or fulvic acids) and inorganic ligands (e.g. fluoride, chloride and sulfate), most but not all of which are soluble. The chemistry of aluminium in water is complex, and many chemical parameters, including pH, determine which aluminium species are present in aqueous solutions. In pure water, aluminium has a minimum solubility in the pH range 5.5–6.0; concentrations of total dissolved aluminium increase at higher and lower pH values (CCME, 1988; ISO, 1994).

 

The fate and behaviour of aluminum in the aquatic environment are very complex. Aluminum speciation, which refers to the partitioning of aluminum among different physical and chemical forms, and aluminum solubility are affected by a wide variety of environmental parameters, including pH, solution temperature, dissolved organic carbon (DOC) content, and the presence and concentrations of numerous ligands. Metals in solution may be present as dissolved complexes, as “free” or aquo ions, in association with particles, as colloids or as solids in the process of precipitating. While most aluminum is released in particulate form, a certain proportion occurs as the dissolved metal and it is this form that is considered easily absorbed and therefore bioavailable to aquatic organisms. The following section therefore discusses aluminum releases in general, with additional emphasis given to dissolved forms.

Hence, as the assessment is based on the element concentration (i. e., Al), physicochemical processes like decomposition and degradation by reaction with water are not relevant. This elemental-based assessment (pooling together of all speciation forms) can be considered as a worst-case assumption for the chemical assessment.

 

The endpoints "Phototransformation in water, soil or air" are not relevant for substances that are assessed using a read-across approach on an elemental basis, i. e., based on the exposure and effects of aluminium, expressed as elemental Al.

For inorganic substance like aluminium salts for which the chemical assessment is based on the elemental concentration (i. e., pooling all inorganic speciation forms together), biotic degradation is an irrelevant process, regardless of the environmental compartment that is under consideration: biotic processes may alter the speciation form of an element, but it will not eliminate the element from the aquatic compartment by degradation or transformation. This elemental-based assessment (pooling all speciation forms together) can be considered as a worst-case assumption for the chemical assessment.

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 also not relevant in the consideration of its environmental fate.