Cobalt molybdate

Bioaccumulation: terrestrial

Description of key information

BCF/BAF (Co): 0.007 to 0.81 (wet weight basis) in plants
BCF/BAF (Mo): 0.2 to 4 (dry weight basis) in plants, and 0.4 to 3.4 (dry weight basis) for earthworms

Additional information

No data for terrestrial bioaccumulation are available for cobalt molybdenum oxide. However, there are reliable data available for different structurally analogue substances and for cobalt and molybdenum measured as element in field investigations, respectively.

The environmental fate pathways and ecotoxicity effects assessments for cobalt metal and cobalt compounds as well as for the 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 cobalt ion and molybdenum ion, released by the parent compound. The result of this assumption is that the ecotoxicology will be similar for all soluble cobalt and molybdenum substances used in the ecotoxicity tests. Therefore, data from soluble cobalt and molybdenum substances are used for the derivation of ecotoxicological and environmental fate endpoints, based on the cobalt ion and molybdenum ion, respectively.With respect to these considerations, data collected on elemental cobalt (e.g. environmental concentrations for Co2+) and elemental molybdenum (e.g. environmental concentrations for Mo2 +) can also be taken into account.

Cobalt

In terrestrial environments, four acceptable biota-to-soil accumulation factors (BSAF-soil) values were identified for two species, Xerocomus badius (bay bolete), and Morus alba (white mulberry). Measurements for X. badius ranged from 0.007 to 0.81, with an average value of 0.15 in the cap, and 0.11 in the stalk (unitless, based on wet-weight). For M. alba, maximum BSAF-soil values of 0.28 and 0.08 were found. One soil study considered the cobalt concentration in a soil solution, thus providing bioaccumulation factors for three different plant species. These values ranged from 0.100 to 0.146, wet-weight. All values obtained from soil studies were reported using dry-weight measurements and then converted to wet-weight values. It is observed that the average BSAF-soil and BAF values of these acceptable studies are all less than one (Environment Canada, 2011).

References:

Environment Canada. Health Canada (2011). Screening Assessment for the Challenge. Cobalt, cobalt chloride, cobalt sulfate.

Molybdenum

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.

This data suggests that Mo is not significantly concentrated from soil to plants, or soil invertebrates with bioconcentration factors (BCF) or bioaccumulation factors (BAF) of < 5, and that there is 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 and foodchain.

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 nitrogenase.