Aluminum zirconium chloride hydroxide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

no hazard identified

Marine water

Hazard assessment conclusion:

no hazard identified

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

no hazard identified

Sediment (marine water)

Hazard assessment conclusion:

no hazard identified

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Aluminum zirconium chloride hydroxide is an inorganic substance which will rapidly dissociate into aluminum, zirconium, chloride and hydroxide ions upon dissolution in the environment. The chemistry of the relevant metals aluminium and zirconium in aqueous solutions is complex. Depending on concentrations, pH and other ions being present, Al and Zr do not exist as simple metal cations, but instead form various species, most relevantly hydroxides and hydroxide-oxides.

Zirconium is one of the 20 most abundant elements in the earth's crust (at approximately 0.03%). Zirconium displays under most environmental conditions, a very low mobility, mainly due to the low solubility of the hydroxide Zr(OH)₄. This limits the concentration of dissolved Zr in most natural solutions (fresh water, seawater as well as soil and sediment porewater) to <0.05 μg/L. Depending on the pH of the environmental medium, different zirconium species exist in solution, including Zr⁴⁺, and various hydroxides. At pH 7, a Zr(OH)₂(CO₃)₂^2-complex may form, but the complex is unstable and Zr(OH)₄forms with decreasing pH. The hydro-bicarbonate (Zr(OH)₄-HCO₃-H₂O) complex may be the most significant Zr complex in natural water (http://www.gtk.fi/publ/foregsatlas, accessed on 12.03.2013).

Results of the solubility testing (OECD Series on Testing and Assessment No. 29) seem to confirm the lack of zirconium solubility at environmentally relevant levels. At a loading of 1 mg Aluminum Zirconium Chloride Hydroxide/L (corresponding to 0.19 µg Al and 0.10 mg Zr) of water or environmental OECD test medium at pH 6 and pH 8, respective dissolved zirconium concentrations were below the detection limit of ca. 0.3 µg/L at all time-points while dissolved Al levels ranging from 0.01 – 0.12 mg/L were measured.

Thus, regarding the environmental toxicity of Aluminum zirconium chloride hydroxide, it can be assumed that toxicity (if any) will not be driven by zirconium. Therefore, full read-across to other aluminum substances considering a typical aluminum content of ca. 19.4% is justified.

Several assessment reports on aluminum are available (ATSDR (2008), Environment Agency (2007), Environment Canada and Health Canada (2010), EURAS (2007), IPCS (1997), RIZA (2002), WHO (2010)). All of them describe that 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. It also enters the environment from anthropogenic sources such as drinking water and wastewater treatment.

 

It is found as a variety of forms, depending on pH, alkalinity, temperature, dissolved organic carbon, dissolved inorganic carbon and anion concentration. Hydroxides are the most common form occurring in water but the chemistry of aluminum becomes more complicated due to the presence of organic and inorganic ligands, which compete for complexation with the hydroxide ion ().

Due to this complicated chemistry all assessment reports also describe that aluminum is hard to assess.

 

Speciation and solubility of aluminum and therefore toxicity depends on pH. Inorganic monomeric forms of aluminum are of particular importance as these are the most toxicologically active species. At pH <5.5, the free ion (Al3+) becomes the prevalent form, along with the inorganic monomeric complexes [AlF, Al(OH)x and Al(SO4)]. The increased availability at this pH is reflected in higher toxicity. At pH 6.0–7.5, solubility declines due to the presence of insoluble Al(OH)3. At higher pH (pH >8.0), the more soluble Al(OH)4 - species predominate, which again increases availability.

 

The presence of natural organic matter can also markedly alter aluminum speciation. Indeed, the presence of moderate amount of organic matter results in complexation of aluminum, being the dominant form when the pH is between 4 and 7. Above pH 7, anionic aluminum hydroxides predominate over the organically complexed aluminum.

In addition, there is a marked tendency for dissolved aluminum-hydroxy and hydroxysilicate species to precipitate, resulting in the removal of some dissolved forms from the water column. This effect is particularly marked at pH values in the range from 6 to 8, the pH range found in most surface waters. The consequence of this is that the dissolved fraction of Al in water is often an insignificant proportion of the total quantity of metal, i.e. the Al(OH)₃precipitate will be the dominant species.

 

The most relevant way of describing toxicity is to express toxicity in terms of concentrations of dissolved aluminum as this is considered the bioavailable part. Many studies describe aluminum toxicity, but only a part of them expresses toxicity as dissolved aluminum concentrations. Therefore numerous studies cannot be compared and cannot be used in the hazard assessment.

 

There is at present no justifiable reason to differentiate between the different aluminum compounds, as no indication is given that aluminum toxicity in the environment would depend on the salt that was applied (as aqueous solution). Moreover, at the moment, there are insufficient data enabling an effect assessment for each aluminum compound. Finally, it is doubtful whether discrimination between aluminum compounds would have an ecological relevance, as the compound will change with time and under various environmental conditions. Hence, it can be concluded that aluminum compounds can be pooled with regard to toxicity.

Conclusion on classification

Aluminum zirconium chloride hydroxide is an inorganic substance which will rapidly dissociate into aluminum, zirconium, chloride and hydroxide ions upon dissolution in the environment. However, zirconium ions will not remain as such in solution and the toxicity (if any) will not be driven by zirconium. Therefore, full read-across to other aluminum substances considering a typical aluminum content of ca. 19.4% is applied. Available data indicate that aluminum salts are relatively non toxic in most waters with circumneutral pH and this was sufficient for the EU Classification and Labelling Committee (1999) to determine that there was no need for classification of aluminum chloride. Other aluminum compounds act similarly in water as aluminum chloride and are in many cases less soluble and non-hazardous.Studies reported in the literature have extensively used test solutions (soluble salts) with aluminum concentrations above that of its solubility limit. Due to physical effects of precipitated material most of these studies are meaningless for the investigation of intrinsic toxicity. Aluminum ions released to surface waters quickly form insoluble aluminum hydroxides in mixing zones. Formation of the complex hydroxide causes the aluminum to drop out of solution very rapidly in neutral and alkaline waters. The dissolved natural background concentrations of aluminum, in most cases, are at equilibrium therefore an addition of aluminum would lead to the precipitation of aluminum compounds from solution and not result in effects to aquatic life.

Therefore, aluminum zirconium chloride hydroxide is not considered an aquatic hazard and classification and labelling is not required according to Directive 67/548/EEC and Regulation (EC) 1272/2008.