Cobalt molybdate

Endpoint summary

Additional information

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.

No adsorption/desorption data are available for cobalt molybdenum oxide, however various reliable data exist for cobalt and molybdenum (measured as environmental concentrations) and different analogue cobalt and molybdenum substances showing statistical or conservative partition coefficients for suspended matter, soil, STP, sediments in freshwater and in coastal waters. For Co, log Kd values for all types ranged from 0.41 to 5.83. For Mo, log Kd values for all types ranged from 2.94 to 3.45.

Cobalt

Information taken from WHO CICAD (2006):

Volatility

Cobalt and inorganic cobalt compounds are nonvolatile. Therefore, they are released into the atmosphere in particulate form. Atmospheric transport depends on particle size and density and meteorological conditions. Coarse particles with diameters >2 μm may deposit within 10 km from the point of emission, while smaller particles may travel longer distances. The mass median diameter of atmospheric cobalt was found to be 2.6 μm in one study. Data on the transformations of cobalt in the atmosphere are limited (WHO CICAD, 2006).

Adsorption

Ultimately, the final repository for cobalt is soil and sediment. Released into water, cobalt may sorb to particles and settle into sediment or sorb directly to sediment. Complexation of cobalt to dissolved organic substances can reduce sediment sorption.

Environmental distribution

Interparticle migration of cobalt can affect the transport of metal ions in sediments. In addition, cobalt can be transported in dissolved form or as suspended sediment by rivers and by sea and ocean currents. Concentration profiles of cobalt in deep water suggest that dissolved amounts decrease with increasing depth and that dissolved cobalt is precipitated in the adsorbed state with oxides of iron and manganese and with crystalline sediments such as aluminosilicate and goethite. Humic substances/humic acids are naturally present in aquatic environments and bind strongly to cobalt. Over time, these complexes may transform into stronger complexes where cobalt is less readily disassociated. The distribution coefficient of cobalt in water varies due to pH, redox conditions, ionic strength, and dissolved organic matter concentrations (WHO CICAD, 2006).

References:

World Health Organization (2006). Concise International Chemical Assessment Document 69. COBALT AND INORGANIC COBALT COMPOUNDS.

Molybdenum

The amount of (high quality) data for the sediment compartment that are represented by the FOREGS-datase is large.Therefore, the typical Kd-sediment of 1,778 L/kg that was derived with the FOREGS-data is considered as a reliable value for this compartment .

For the particulate suspended matter compartment, it was decided that the average of all relevant values could be put forward as the typical Kd for suspended particulate material. The derived value of 2,793 L/kg (log Kd of 3.45) is about a factor of 1.6 higher than the Kd that was found for the sediment compartment. This finding is in line with the observations for other metals where the Kd,SPM was also somewhat higher compared to the Kd for sediment.

For the terrestrial compartment, it was decided to put forward the typical value of 871 L/kg (Log Kd: 2.94) as reported by Crommentuyn et al. (1997).

References:

Crommentuijn, T., Polder, M.D. and van de Plassche, E.J. (1997). Maximum Permissible Concentrations and Negligible Concentrations for metals, taking background concentrations into account. National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands. Report N° 601501 001.