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Read-across approach

In the assessment of the environmental fate and pathways of 2-ethylhexanoic acid, molybdenum salt (CAS: 34041-09-3), a read-across approach from data for the metal and organic ions is followed. This read-across strategy is based upon the assumption that upon release to the environment and dissolution in aqueous media, 2-ethylhexanoic acid, molybdenum salt will completely dissociate and only be present in their dissociated form, i.e. as molybdate and the 2-ethyl hexanoate anion.

Upon dissolution in water, it is indeed predicted that metal carboxylates dissociate completely into the metal and the organic anion at environmentally relevant conditions. No information is available on the stability constants of 2-ethylhexanoic acid, molybdenum salt, but predictions of stability of another molybdenum carboxylate (Mo isovalerate) in a standard ISO 6341 medium (2 mM CaCl2, 0.5 mM MgSO4, 0.77 mM NaHCO3 and 0.077 mM KCl, pH 6 and 8) clearly show that monodentate ligands such as carboxylic acids have no potential for complexing molybdenum ions in solution (<1% of total metal concentration complexed at 0.001 mM Mo) and that molybdenum will be present as the molybdate anion (Visual minteq. Version 3.0, update of 18 October 2012. http://www2.lwr.kth.se/English/OurSoftware/vminteq/index.html).

Upon dissolution and dissociation of 2-ethylhexanoic acid, molybdenum salt into molybdate and the 2-ethyl hexanoate anion, both constituent ions will each show its proper (bio) degradation, bioaccumulation and partitioning behaviour in the environment, as reported for the corresponding metal ion and carboxylic acid (molybdate and 2-ethyl hexanoic acid). For molybdenum, read-across is made from the dossier on the soluble disodium molybdate salt, since molybdate is the dominant molybdenum species under environmental relevant conditions. The environmental fate and behaviour for the metal and organic moieties is predicted to be clearly different from each other, resulting in a different relative distribution over the environmental compartments (water, air, sediment and soil).