Cobalt molybdate

Toxicity to aquatic plants other than algae

Description of key information

EC50 (4d) = 0.52 mg cobalt molybdenum oxide/L (Spirodela polyrhiza) for growth rate (read-across from cobalt chloride)

Key value for chemical safety assessment

EC50 for freshwater plants:

0.52 mg/L

Additional information

No data on the toxicity to aquatic plants other than algae are available for the test substance 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 chronic single-species toxicity tests resulting in high quality EC50 values (expressed as Co) for aquatic plants are summarised in the WHO CICAD, 2006 (see attached table).

Results are available for Spirodela polyrhiza (Gaur et al., 1994) and Azolla pinnata (WHO CICAD, 2006)with EC50 (4d) values of 0.14 and 0.24 mg Co/L, respectively, equivalent to recalculated values of 0.52 and 0.89 mg cobalt molybdenum oxide/L, respectively.
In the key study, the effects of cobalt chloride on greater duckweed (Spirodela polyrhiza) were investigated in a static 4-d test at nominal concentrations of 0.85, 1.7, 8.5, 17.0 and 85.0 µM Co (Gaur et al., 1994). As a result, an EC50 of 0.14 mg Co/L was obtained for growth, equivalent to 0.52 mg cobalt molybdenum oxide/L.
Further results for aquatic plants are available and comprised in the attached table.

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

Molybdenum

Freshwater:

The toxicity of molybdenum to freshwater aquatic plants was tested by De Schamphelaere et al. (2008) on Lemna minor, resulting in a 7d-ErC10 of 241.5 mg Mo/L.

Marine:

The toxicity to of molybdenum to marine aquatic plants was investigated on the red macroalgae Ceramium tenuicorne by Le Page et al. (2010). As a result, a 7d-ErC10 of 274 mg Mo/L was obtained.

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.