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Aluminium lanthanum trioxide appears to have a low potential for short-term toxicity to aquatic invertebrates and toxicity to freshwater algae.

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The solubility of Aluminium lanthanum trioxide (AlLaO3) in environmental media is expected to be low since dissolution in water resulted in La concentrations < 0.01 mg/L and Al concentrations < 0.03 mg/L after 34 days. The ecotoxicological moieties of concern are aluminium and lanthanum ions. Thus, in the assessment of aquatic toxicity to invertebrates (short-term) and algae, data available for different aluminium and lanthanum substances are read-across since aluminium and lanthanum ions are the common ecotoxicological moieties of concern.

The dissolution of aluminium lanthanum trioxide in water results in Al (3+) (=Al(H2O)6 (3+)) ions and La (3+) ions. The effects of the substance aluminium lanthanum trioxide are predicted to be equal to the effects of Al (3+) ions and La (3+) ions. Based on the low solubility of aluminium lanthanum trioxide (Al concentrations < 0.03 mg/L and La concentrations < 0.01 mg/L after 34 days in water at a loading of 100 mg/L) and EC50 values available for Al (3+) ions and La (3+) ions, Aluminum lanthanum trioxide appears to have a low potential for short-term toxicity to aquatic invertebrates and toxicity to freshwater algae as explained further below.

Aluminum

Aluminium has a low mobility under most environmental conditions, although below pH 5.5 its solubility increases. Because of its amphoteric nature, aluminium may also be mobilised in anionic form under strongly alkaline conditions at pH > 8. The speciation of aqueous Al is dependent on pH and the presence and nature of complexing ligands. In aqueous solutions, unhydrolyzed Al (3+) (aq) does not remain as free ion, but is surrounded by six molecules of water Al(H2O)6 (3+). As solution pH increases, protons are removed from the coordinated waters giving a series of hydrolysis products: Al(H2O)5(OH) (2+); Al(H2O)4(OH)2 (+); Al(H2O)3(OH)3; Al(H2O)2(OH)4 (-); Al(H2O)(OH)5 (2-). Thus, in the absence of significant concentrations of complexing ligands, the dominant form of dissolved Al below about pH 4.5 is Al(H2O)6 (3+). Above pH 4.5, the hydrolysed forms Al(H2O)5(OH) (2+) and Al(H2O)4(OH)2 (+) are predominant. At low pH, organic ligands, including humic and fulvic acids, and inorganic ligands, such as fluoride, readily complex with dissolved aluminium. As a result of organic complexation, particularly through chelation, a significant proportion of Al is usually in colloidal or particulate forms. Concentrations of dissolved Al are generally low in most natural waters (Salminen et al. 2015 and references therein). Endpoints are expressed as a function of total Al, rather than as dissolved or monomeric Al. For most test solutions with pH from 6 – 8, Al is largely insoluble, and dissolved and monomeric concentrations remain relatively constant even with large increases in total or nominal Al. Thus, dose-dependent responses observed by aquatic organisms can only be reliably quantified using total Al across the full pH range from 5.5 - 8.0. 

Algae:

The available reliable EC50 values from 11 algal growth inhibition studies, all performed with Pseudokirchneriella subcapitata, vary from 0.2 to > 4.9 mg Al/L (total). Most of the variation in results can be explained by differences in parameters of the test media, i.e. mostly differences in pH and DOC and to a lesser extent hardness.Under standard test (pH, DOC and hardness) conditions, however, aluminium appears to have a low potential for toxicity to freshwater algae.

Invertebrates:

The available reliable EC/LC50 values of five aquatic invertebrate species from twelve short-term toxicity studies vary from 0.071 to > 99.6 mg Al/L (total). Most of the variation in results can be explained by differences in pH, hardness and DOC of the test media. Under standard test (pH, DOC and hardness) conditions, however, aluminium appears to have a low potential for toxicity to freshwater invertebrates.

Lanthanum

Under typical environmental conditions, lanthanum (3+) ions and lanthanum oxides and hydroxides are only sparingly soluble. Further, dissolved lanthanum is mainly complexed to carbonates and dissolved organic matter (DOM). With pH increasing from 6 to 9, concentrations of La-DOM complexes and free La (3+) ions (if any) decrease and complexation and precipitation of lanthanum carbonate complexes increases. Thus, speciation and availability of lanthanum are strongly influenced by pH.

Algae:

In a growth inhibition testaccording to OECD TG 201, the toxicity of a soluble lanthanum salt (LaCl3) to Desmodesmus subspicatus was examined. The 72-h ErC50 and ErC10 of 16 mg/L La and 1.3 mg/L La (both based on measured) corresponding to 24.6 mg/L AlLaO3 and 2.0 mg/L AlLaO3, respectively, indicate that lanthanum has a low potential for toxicity to freshwater algae.

Invertebrates:

In an acute immobilisation test according to OECD TG 202, the toxicity of a poorly soluble lanthanum substance (La2O3) to Daphnia magna was examined. The 48-h EC50 of > 100 mg/L La2O3 mg/L (nominal 85.3 mg/L La) corresponding to > 326 .8 mg/L AlLaO3 indicate that lanthanum is not toxic to freshwater invertebrates. Supporting studies of Daphnia carinata (48-h EC50 of 1.2 mg/L La corresponding to 1.8 mg/L AlLaO3), Hyalelle azteca (7d-EC50 of 1.7 mg/L La corresponding to 2.6 mg/L AlLaO3), Tubifex tubifex (96-h EC50 29.4 mg/L La corresponding to 45.3 mg/L AlLaO3) and Cypris subglobosa (48-h EC50 of 41.5 mg/L La corresponding to 63.9 mg/L AlLaO3) further point to a low potential for toxicity to freshwater invertebrate species.

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