Dodecaaluminium trimolybdenum dodecaoxide

Endpoint summary

Additional information

Aluminium molybdenum oxide is an inorganic salt of a weak Lewis base and acid. The water solubility test shows that the solubility of aluminium and molybdenum increases with the loading rate of the test item (50 – 700 mg/L) at 20.0 °C and pH 4.34 -4.78. Therefore salt hydrolysis may proceed, when the substance is transferred into the aquatic environment. Different aqueous aluminium and molybdate species will be formed depending on the pH and redox potential of the aquatic environment.

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 result in form of poorly soluble aluminium hydroxide. This hydrolysis reaction is very rapid and is completed within 1-7 seconds.

Aluminium hydroxide is amphoteric and soluble in both strong acids and bases. In acidic solution (pH < 4) aluminium hydroxide dissolves to form mostly Al³⁺ions (or more specific as Al(H₂O)₆^3-ions) and in alkaline solution (pH > 8) the aluminate ion Al(OH)₄^-is the totally dominating species. At pH 4.0, mono- and dimeric aluminium species [Al(OH)₂(H₂O)_2-3]⁺ and [Al₂O₂(OH)(H₂O)_0-5]⁺were detected as main products. With increasing pH, hydrolysis and polymerization increased. At pH 5.0, aluminium species mainly aggregated and assembled to median polymeric species (Al₆-Al₁₀species) and these further to large polymeric species (Al₁₁- Al₂₁). At pH 5.8 metastable median and large polymers decomposed into small aluminium species and disaggregated into dimeric species. With pH 6.4 the majority of aluminum formed to Al(OH)₃amorphous flocs. Based on the available data on water solubility of different molybdenum compounds and on the determination of dissolved speciation by UV spectroscopy, it could be seen that at low molybdate concentrations, dissolved molybdate exist in water predominantly as H2MoO4 or [HMoO4]- between pH 2 and 4.3. The [MoO4]2- species increases along with the increasing of pH. Above pH 4.5, [MoO4]2- is the only species in the water (Cruywagen and Heyns, 1987).

In general, (abiotic) degradation is an irrelevant process for inorganic substances therefore the environmental half-life of aluminium hydroxide is not required.

Biodegradation in water, sediment and soil is not an applicable endpoint for aluminium molybdenum oxide as the substance is inorganic.

No bioaccumulation data are available for aluminium molybdenum oxide, however various reliable data exist for aluminium and molybdenum (measured as environmental concentrations) and different analogue aluminium and molybdenum substances.

For aluminium, the available evidence shows the absence of aluminium biomagnification across trophic levels both in the aquatic and terrestrial food chains. The existing information suggests not only that aluminium does not biomagnify, but rather that it tends to exhibit biodilution at higher trophic levels in the food chain.

For molybdenum, all of the 27 BCF/BAF reported are below 100 with the exception of one BAF measured for a mollusc exposed to background Mo water concentrations (BAF of 164). The data demonstrates that molybdenum, like other essential elements, shows homeostatic control by organisms. Limited information on transfer of Mo through the food chain indicates that molybdenum does not biomagnify in aquatic food chains. For the terrestrial compartment, the data suggests that Mo is not significantly concentrated from soil to plants, or soil invertebrates with BCF/BAF of < 5, and that there is no further significant increase in concentration from diet to mammals or birds.

No adsorption/desorption data are available for aluminium molybdenum oxide, however various reliable data exist for aluminium and molybdenum (measured as environmental concentrations) and different analogue aluminium and molybdenum substances showing statistical or conservative partition coefficients for suspended matter, soil, STP, sediments in freshwater and in coastal waters.

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 amount of aluminium bound to particles as a result of surface complexation (i.e. adsorption) was shown to be pH dependent, but was typically less than 8% of the total aluminium at pH 6, and was further reduced to below 1% at pH values above 7. The corresponding Log Kd values for this distribution ranged between 3 and 5. 

For Mo, log Kd values for all types ranged from 2.94 to 3.45.