Cobalt molybdate

Toxicity to terrestrial arthropods

Description of key information

NOEC (28d, mortality) = 371 mg cobalt molybdenum oxide/kg soil dw (Folsomia candida) (read-across from cobalt chloride hexahydrate)

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for soil dwelling arthropods:

371 mg/kg soil dw

Additional information

No data on toxicity to terrestrial arthropods are available for cobalt molybdenum oxide. However, there are reliable data available for different structurally analogue substances.

The environmental fate pathways and ecotoxicity effects assessments for cobalt metal and cobalt compounds as well as for 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 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 in the derivation of ecotoxicological and environmental fate endpoints, based on the cobalt ion and molybdenum ion, respectively.

Cobalt

Data on soil-dwelling invertebrates resulting in high quality EC50/NOEC values (expressed as Co) are summarized in the WHO CICAD (2006).

The only study on an arthopod species, the springtail Folsomia candida, was conducted with cobalt chloride hexahydrate according to ISO-Guideline 11267 on two different soils (artifical soil according to OECD 207 and standardised field soil LUFA 2.2) by Lock et al. (2004). The more sensitive 28-day NOEC of 100 mg Co/kg soil dw (371 mg/kg soil dw, recalculated value for cobalt molybdate) was measured on standardised field soil (pH CaCl2 5.49) while on artificial soil with a pH(CaCl2) of 7.14, the 28-day NOEC was found to be 1000 mg Co/kg soil dw (3714 mg/kg soil dw, recalculated value for cobalt molybdenum oxide). Cation exchange capacity and pH are indicated as main factors influencing cobalt bioavailability.

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

Molybdenum

For the arthropod invertebrate toxicity assay, Folsomia candida was used as a test species. Only 3 soils resulted in reliable, bounded NOEC values. In all 8 other soils, no toxic effect was observed at the largest dose tested (unbounded NOEC values between >2628 and 3395 mg added Mo/kg dw. The reliable NOEC/EC10 values taken forward ranged from 37.9 to 1865 mg added Mo/kg dw. All data are based on added measured Mo concentrations in soil.

Not much could be concluded regarding the results of the 3 aged soils given that already in the spiked soils, no effects were observed. In one of the 3 aged soils, an effect was noted, although at a concentration greater than the unbounded NOEC in the spiked soil.

Conclusion
As the effect values derived from analogue cobalt compounds are considerably lower than those derived from analogue molybdenum substances, it can be reasoned that the cobalt ion will account for the effects in ecotoxicological testing. Hence, it was concluded to put forward the most sensitive and reliable results derived from analogue cobalt compounds for assessment purposes, and recalculate them for CoMoO4.