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Environmental fate & pathways

Bioaccumulation: terrestrial

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Description of key information

Data that were retrieved, suggest that molybdenum, although not homeostatically controlled in terrestrial plants and invertebrates, is not largely concentrated from soil into plants, or soil to invertebrates, with BCF/BAF ranging from 0.2 to 4 (dry weight basis) in plants and 0.4 to 3.4 (dry weight basis) for earthworms, so well below 100, and that there is no significant concentration increase from diet to mammals or birds. This suggests that biomagnification, if any, is not significant in the terrestrial foodchain.

More detailed information can be found in the section "Additional information" and in the Background Document 'Environmental fate properties of molybdenum", which is attached in the technical dossier in IUCLID Section 13.

Key value for chemical safety assessment

Additional information

Mo concentration ranges in environmental matrices have been compiled. The data includes concentrations of Mo in the environmental compartments, excluding geogenic enriched areas, and at moderate levels below Mo concentrations causing a toxic effect.

These data show that Mo is not significantly concentrated from soil to plants, or soil invertebrates with bioconcentration factors (BCF) or bioaccumulation factors (BAF) of < 5. Plant Mo concentrations do rise linearly with increasing soil Mo up to 20 mg Mo/kg in the soil and up to 10 mg/kg in the grass (no complete homeostatic control in this Mo-range), but instead a slow accumulation. The linear line with a significant intercept illustrates that the plant/soil BCF value (the concentration ratio) reduces about a factor 3 between 1 and 10 mg Mo/kg soil. The concentrations of Mo in the earthworms near background are all low with a range in BAF of 0.35-3.4 and an average value of 1.5). There is also no further significant increase in concentration from diet to mammals or birds, even including organs such as kidney or liver (diet tissue concentration ratios <10 and even <1 for muscle tissue). This suggests that biomagnification of Mo, if any, is not significant in the terrestrial compartment.

Eisler (1989) made a more exhaustive compilation of environmental concentrations of Mo. That review concluded equally that Mo concentrations in plants, mosses and wildlife tissues (liver and kidney included) are well below 10 mg/kg dry weight, excluding legumes (e. g. clover) that contain up to 28 mg/kg dry weight. Legumes –N2 fixing plants- require higher levels of Mo as the latter element is required for the proper functioning of the enzymes nitrate reductase and the terrestrial foodchain.