Dodecaaluminium trimolybdenum dodecaoxide

Toxicity to soil microorganisms

Additional information

No data on toxicity to soil microorganisms are available for aluminium molybdenum oxide. However, there are reliable data available for different analogue substances.

The environmental fate pathways and ecotoxicity effects assessments for aluminium metal and aluminium compounds as well as for molybdenum metal and molybdenum compounds is based on the observation that adverse effects to aquatic, soil- and sediment-dwelling organisms are a consequence of exposure to the bioavailable ion, released by the parent compound. The result of this assumption is that the ecotoxicological behaviour will be similar for all soluble aluminium and molybdenum substances used in the presented ecotoxicity tests. As aluminium molybdenum oxide has shown to be only slightly soluble in water (pH 4.5, 7d) and poorly soluble in ecotoxicity test media (pH 7.5-8.5, 96h), it can be assumed that under environmental conditions in aqueous media, the components of the substance will be present in a bioavailable form only in minor amounts (Mo) or hardly, if at all (Al). Within this dossier all available data from soluble and insoluble aluminium and molybdenum substances are taken into account and used for the derivation of ecotoxicological and environmental fate endpoints, based on the aluminium ion and molybdenum ion. All data were pooled and considered as a worst-case assumption for the environment. However, it should be noted that this represents an unrealistic worst-case scenario, as under environmental conditions the concentration of soluble Al³⁺and MoO₄^2-ions released from aluminium molybdenum oxide is negligible (Al) or low (Mo), respectively.

Aluminium

Aluminium, aluminium powders and aluminium oxide are non hazardous (not classified for the environment). Aluminum (Al) is the most commonly occurring metallic element, comprising eight percent of the earth's crust (Press and Siever, 1974) and is therefore found in great abundance in both the terrestrial and sediment environments. Concentrations of 3-8% (30,000-80,000 ppm) are not uncommon. The relative contributions of anthropogenic aluminium to the existing natural pools of aluminium in soils and sediments is very small and therefore not relevant either in terms of added amounts or in terms of toxicity. Based on these exposure considerations additional sediment and/or soil testing is not warranted. More information about exposure based waiving for aluminium in soil and sediments can be found in attached document (White paper on exposure based waiving for Fe and Al in soils and sediments final 15-03-2010. pdf).

Molybdenum

A total of 10 topsoils with contrasting properties that may affect the toxicity of Mo in soil were collected and on each of these soils a series of 3 microbial assays (nitrification, glucose induced respiration and mineralisation of plant residues) were performed after spiking with sodium molybdate. The microbial toxicity assays resulted in 18 individual high quality EC10 selected for the assessment. The EC10 values ranged from 10 to 3840 mg added Mo/kg dry weight soil. Additionally, 3 soils were aged outdoors after spiking with sodium molybdate. After 6 and 11 months, subsamples were collected and the same ecotoxicity tests as above were conducted on these soils. In general, this showed that long-term equilibration of Mo in soils decreases its toxicity to micro-organisms. The results of the toxicity in aged soils are used to determine a Leaching/Ageing factor to correct for the effect of spiking on the toxicity of Mo in soil organisms.

For the microbial assays a total of 18 individual high quality EC10 values (for 3 different microbial assays) are selected. These values range from 10 mg added Mo/kg dw (for the glucose induced respiration assay in soil 3) to 3840 mg added Mo/kg dw (for the substrate induced nitrification assay in soil 10). All data are based on added nominal Mo concentrations in soil. A dose confirmation showed an average recovery of 103% for the spiked soils for the nitrification assay and 98% for both the glucose induced respiration and plant residue mineralisation assays.

The substrate induced nitrification, glucose induced respiration and plant residue mineralisation assays yielded reliable, bounded NOEC values for 8, 6 and 4 soils out of 10, respectively. In all the other soils, no toxic effect was observed at the highest dose tested (10000 mg added Mo/kg dw).

For the 3 aged soils (soil 4,5 and 6), the comparison of Mo in freshly spiked and 11 -month aged soils show that long-term equilibration of Mo in soil generally decreases its toxicity to micro-organisms. No toxicity was observed in 2 of the 3 aged soils at the highest concentrations left in these soils. In one soil (soil 6), toxicity was still observed in the 11 -month aged soil for the glucose induced respiration and plant residue mineralisation assays.

The results of the toxicity in aged soils is used to determine a leaching/ageing factor to correct for the effect of spiking on the toxicity of Mo in soil organisms.

Author, year	Endpoint	Value [mg Mo/kg soil dw]
Smolders and Buekers, 2009	28 d EC10	35 - > 10000
Smolders and Buekers, 2009	24 h EC10	10 - > 10000
Smolders and Buekers, 2009	28 d EC10	164 - > 10000