Dodecaaluminium trimolybdenum dodecaoxide

Long-term toxicity to fish

Description of key information

EC10 (78d) = 43.2 mg Mo/L for Oncorhynchus mykiss (OECD 210) (read-across from sodium molybdate dihydrate)
EC10 (60d) = 0.078 mg Al/L for Salvelinus fontinalis (read-across from aluminium sulphate)

Additional information

No data on long-term toxicity to fish 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

Long Term Fish Toxicity Literature Review: Four long-term reliable chronic toxicity studies to two species of fish (Pimephales promelas and Salveninus fontinalis) were identified as acceptable from the published literature. NOECs and EC10s ranged from 0.088 to 2.3 mg Al/L and 0.078 to 5.19 mg Al/L, respectively. 

The following information is taken into account for long-term fish toxicity for the derivation of PNEC:

The Al BLM developed using gill accumulation data from S. salar was applied to the chronic Pimephales promelas data (Oregon State University Aquatic Toxicology Laboratory 2010; Figure 7.1.1.1.2.-1). Application of the model to new data requires development of a critical accumulation value appropriate for the exposure duration and toxicity endpoint. In addition, calibration of the model to these data benefited from two other changes in parameter values. First, since the chronic endpoints for this species and in these test conditions were at much higher aluminium concentrations and saturation of NOM binding sites included in the model was beginning to occur, resulting in a somewhat reduced predicted effect of NOM compared with the observed effect. The binding site density for NOM was increased by two fold to provide adequate binding sites at these high Al concentrations. In addition, although the effect of hardness on observed aluminium toxicity was consistent in acute and chronic exposures, the predicted effect of hardness could be improved by a small change in the binding strength of Ca (i.e. the log K for binding at the biotic ligand was increased from 4.2 to 4.8. 

After application of the Al BLM, the variability in the response curve between effects of aluminium on the biotic ligand was reduced compared with response curve based on total aluminium (Figure 7.1.1.1.2.-2). Values for critical accumulation were estimated

directly from the predicted response curve on the biotic ligand to establish the CA10, or the critical accumulation level that results in a chronic effect of 10% (in this case a reduction in growth). 

Figure 7.1.1.1.2.-3 provides an evaluation of the ability of the long-term fish BLM to predict EC10 values. In this case, most of the EC10 values are predicted within 2-fold of the reported EC10 values, and all of the predicted EC10 values are within 4-fold of the reported values. 

Molybdenum

Freshwater:

Two studies have been identified that report chronic effect levels for the rainbow trout Oncorhynchus mykiss and produced high-quality effects data (Davies et al., 2005; Parametrix, 2008). The first study reported NOEC values for survival as effect parameter, whereas the second study presented NOEC- and EC₁₀-values for survival and biomass growth. Comparable effect levels (NOECs) were found for survival in both studies. Biomass growth, however, was found to be a more sensitive effect parameter than survival. EC₁₀-values were available based on a single test and on the combined effect-concentration relationship of two tests. Arguments can be put forward why a specific test result should be preferred over the other value. On one hand, combining two tests implies mixing the outcome of test results that were obtained with to different batches of organisms. The normalised effect-concentration relationship, however, shows a clear decrease from 0% effect to >95% effect. Consequently, the confidence interval that is associated with the combined data set is also narrower than the confidence interval around the EC₁₀of the second test, as only small but significant effects (10-22%) were observed at the two highest effect levels. From a conservative point of view, it was decided to use the EC₁₀-value of 43.2 mg Mo/L for assessment purposes.

For the fathead minnow Pimephales promelas two reliable studies were identified: Canton et al. (2006) and Parametrix (2007). High quality data values were available for three endpoints, with (biomass) growth being more sensitive than survival in both studies. As EC₁₀-values are preferred over NOEC-values for risk assessment purposes, the geometric mean of 60.2 mg Mo/L (EC₁₀-values of 39.9 and 90.9 mg Mo/L) was selected as chronic no-effect value for P. promelas. 

A 20-week test with Oncorhynchus kisutch obtained a NOEC of > 19.5 mg Mo/L (m), based on mortality, deformations and hatching percentage (Ennevor, 1993), and a 12-month study conducted with Oncorhynchus mykiss led to a NOEC of > 17 mg Mo/L (m), based on mortality, growth, hematocrits and development of eggs (McConnell, 1977).

 

Marine Water:

One reliable study has been identified for the marine environment, conducted with the sheepshead minnow Cyprinodon variegatus (Parametrix, 2009). Dry weight was the most sensitive endpoint (other endpoints: embryo/larval survival, biomass). For this endpoint a reliable 28d-EC₁₀of 84.1 mg Mo/L has been reported, and this value is used for assessment purposes.

Conclusion

The effect values derived from analogue aluminium compounds are considerably lower than those derived from analogue molybdenum substances. However, these values were not considered for the assessment as it can be assumed that under environmental conditions in aqueous media, aluminium will predominantly be present as insoluble species (Al(OH)₃) and hence, will be present in a bioavailable form only in minor amounts, if at all. Therefore, it was concluded to put forward the most sensitive and reliable results derived from analogue molybdenum compounds for assessment purposes. Still, it should be noted that his represents an unrealistic worst-case scenario as under environmental conditions in aqueous media, the components of the sparingly soluble substance will be present in a bioavailable form only in minor amounts, and hence, the concentration of soluble MoO₄^2-ions released is very low.