Registration Dossier

Administrative data

Description of key information

The available studies cover the range of soluble and poorly soluble molybdenum substances and also different chemical forms (metal, oxides, salts). All tested molybdenum substances show a very low order of toxicity. To avoid unnecessary testing, read-across is applied to ammonium octamolybdate, which is also considered to be non-toxic following acute exposure via the oral, dermal or inhalation route. It is considered to be very unlikely that the ammonium moiety adds any reasons for concern regarding acute toxicity, based on the ubiquitous physiological presence in biota and/or their essential role in human physiology. Thus:
Estimated LD50oral > 2000 mg/kg bw (based on read-across)
Estimated LD50dermal > 2000 mg/kg bw (based on read-across)
Estimated LC50inhalation, 4h > 5 g/m³ (based on read-across)

Key value for chemical safety assessment

Additional information

Experimental investigations in laboratory animals on acute toxicity after oral, dermal or inhalation exposure are available for a number of soluble an poorly soluble molybdenum substances, including Mo (metal), MoO3, MoO2, sodium molybdate, ammonium dimolybdate and roasted molybdenite concentrate. All available acute oral LD50(covering the entire range of solubilities and valencies) are in excess of 2,000 mg/kg. Given that it has been shown for all molybdenum substance groups that the only species formed upon contact with aqueous media is the molybdate anion, read-across among all molybdenum substances is considered justified without restriction. In consequence, no classification is required for acute oral toxicity.

 

Regarding acute dermal toxicity, the LD50of soluble and moderately soluble molybdenum substances was determined to be larger than the limit test dose of 2000 mg/kg in all tests. Together with the poor rate of dermal absorption of soluble molybdate species (ca. 0.2%), it is considered justified to read-across to poorly soluble molybdenum species also, resulting in no need for classification for acute dermal toxicity.

 

In acute inhalation toxicity studies, there was a complete absence of mortalities in all studies covering the entire range of soluble, moderately soluble and poorly soluble molybdenum substances. Correspondingly, the LC50(4h) for all tested substances was either above the maximum attainable test concentration or the limit test concentration. As a consequence, no classification for acute inhalation toxicity is required for any of the tested molybdenum substances.

Justification for classification or non-classification

Based on the classification criteria laid down in Regulation (EC) No 1272/2008, ammonium octamolybdate does not require classification for acute toxicity. This conclusion is based on standard experimental investigations in laboratory animals with this substance and/or read-across to a number of other molybdenum compounds