Registration Dossier

Administrative data

Key value for chemical safety assessment

Additional information

The following recently conducted guideline-conform, highly reliable state-of-the-art genotoxicity tests with a soluble molybdenum substance (sodium molybdate) are available:

- an AMES bacterial reverse mutation assay (Beevers, 2009),

- an in vitro micronucleus assay in human lymphocytes (Taylor, 2009), and

- an in vitro gene mutation assay (tk) in mouse lymphoma cells (Lloyd, 2009).

All three tests produced unequivocally negative results, and thus provide strong evidence for an absence of concern for genotoxic effects of molybdenum substances. Since the substance tested represents a highly soluble molybdate, and all molybdenum substances regardless of their solubility, speciation and valence have been shown to transform rapidly to molybdate anions upon dissolution in aqueous media, these results can be read across to all other molybdenum substances without restriction. Because of their ubiquitous physiological presence in biota and/or their essential role in human physiology, the sodium/ammonium/calcium/iron moieties in some of the molybdenum substances are not considered to be of concern for genotoxicity.

In conclusion, no classification of any molybdenum substance for genotoxicity is required.

Apart from these high quality, reliable GLP test results, a large number of published studies exist of varying quality and extent of documentation, which is why these were subjected to a detailed quality and reliability screening, the outcome of which can be summarised as follows:

(i) unequivocally negative results were obtained in guideline-conform, valid bacterial reverse mutation assays for high purity (moderately soluble) molybdenum trioxide (studies by Jones, 2004 and Zeiger et al., 1992). Negative results were also obtained in the same test system with (highly soluble) sodium and ammonium molybdates, which however from a perspective of formal regulatory compliance are considered incomplete because of the selected tester strains (studies by Armitage, 1997 and Kubo et al. 2002).

(ii) all in vitro clastogenicity test considered as assignable and reliable with or without restrictions are negative.

(iii) in view of the unequivocally negative results in all three in-vitro key studies, the conduct of any further in vivo testing would not be required. Already available in vivo studies were subjected to a thorough evaluation and were found to be seriously flawed and of poor quality, and were thus assigned reliability grades of either 3 or 4. In this context it is explicitly noted that set of studies published by Titenko-Holland (1998) have already previously been criticised and disregarded by the Classification and Labelling Committee of the ECB as deficient during discussions on molybdenum trioxide in 2004.


Short description of key information:
Three recently conducted guideline-conform, highly reliable state-of-the-art genotoxicity tests produced unequivocally negative results, and thus provide strong evidence for an absence of concern for genotoxic effects of molybdenum substances, which is supported by reliable supplementary data.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the review of key experimental studies as well as supportive information on genetic toxicity, no classification of molybdenum substances is required.