Cobalt molybdate

Sediment toxicity

Description of key information

LC50 (48h) = 211 mg cobalt molybdenum oxide/L (Chironomus tentans) (read-across from cobalt chloride hexahydrate)

Additional information

No data on sediment toxicity 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 single-species toxicity tests resulting in high quality L(E)C50 values (expressed as Co) for sediment-dwelling species (n=5) are summarised in the WHO CICAD, 2006 (see attached table).

Data on five species were available for the assessment. In the key study, Chironomus tentans was tested according to APHA guidelines (Standard methods for the examination of water and waste water, 1981) in a static 48-hour test, with cobalt chloride hexahydrate as test substance (Khangarot and Ray, 1989). As a result, a LC50 value of 57 mg Co/L was obtained, equivalent to 211 mg cobalt molybdenum oxide/L. For further species (Branchiura sowerbyi, Tubifex tubifex and Lumbriculus variegatus) 96 -hour LC50 values ranged from >45 to 239 mg Co/L, resulting in recalculated values of 167 to 888 mg cobalt molybdenum oxide/L. The results represent worst-case conditions since the solution will naturally contain more cobalt than would be available in a sediment matrix. The most sensitive value, however not conducted on a standard species, was derived from tests with the mayfly Ephemerella subvaria, resulting in a 96-hour LC50 of 18 mg/L (WHO CICAD, 2006).

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

Molybdenum

One study is available on a short-term toxicity test with Chironomus tentans according to ASTM and US EPA guidelines (GEI, 2009). The test was conducted with sodium molybdate dihydrate and resulted in a 48 -hour LC50 of 7533 mg Mo/L.

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.