Aluminum cobalt oxide

Short-term toxicity to aquatic invertebrates

Description of key information

EC50 (48 h) = 1.49 mg Co/L (Daphnia magna) (read-across from cobalt chloride hexahydrate)

Additional information

No data on the short-term toxicity to aquatic invertebrates are available for the test substance cobalt aluminium 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 aluminium metal and aluminium 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 ecotoxicological behaviour will be similar for all soluble cobalt and aluminium substances used in the ecotoxicity tests.

As cobalt aluminium oxide has shown to be highly insoluble with regard to the results of the transformation/dissolution test protocol (pH 6, 28 d), it can be assumed that under environmental conditions in aqueous media, the components of the substance will be present in a bioavailable form only in minor amounts, if at all. Within this dossier all available data from cobalt and aluminium substances are pooled and used for the derivation of ecotoxicological and environmental fate endpoints, based on the cobalt ion and aluminium ion. For cobalt, only data from soluble substances were available and for aluminium, both soluble and insoluble substance data were available. All data were pooled and considered as a worst-case assumption for the environment. However, it should be noted that this represents an unrealistic worst-case scenario, as under environmental conditions the concentration of soluble Co2+ and Al3+ ions released is negligible.

Cobalt
Data on acute single-species toxicity tests resulting in high quality L(E)C50 values (expressed as Co) for freshwater invertebrates (n=11) are summarised in the WHO CICAD, 2006 (see attached table).

Acute data for Daphnia magna were extracted and used in the effects assessment. The LC50(48 h) values ranged from 1.1 mg Co/L, tested as cobalt chloride hexahydrate to 6 mg Co/L, tested as cobalt sulfate. The key study (Khangarot and Ray, 1989) showed an acute toxicity resulting in an EC50(48 h) of 1.49 mg Co/L.

Studies on other invertebrate species such as rotifers, different copepod species and crayfish showed a range of EC50 values from 3.4 to 27.8 mg Co/L, tested as cobalt chloride hexahydrate (WHO CICAD, 2006). These data are comprised in the attached table.

 

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

Aluminium

Twelve short-term toxicity studies to six aquatic invertebrate species were identified for informational purposes. The available 48-h EC/LC50 values varied from 0.071 to > 99.6 mg Al/L.The acute NOECs (48 h) varied from > 0.005 to > 0.135 mg Al/L. Most of the variation in results can be explained by differences in hardness and DOC in the test media.

Conclusion
As the effect values derived from analogue cobalt compounds are considerably lower than those derived from analogue aluminium substances, it can be reasoned that the cobalt ion will mainly account for ecotoxicological effects of the substance. Hence, it was concluded to put forward the most sensitive and reliable results derived from analogue cobalt compounds for assessment purposes. Still, it should be noted that this represents an unrealistic worst-case scenario as under environmental conditions in aqueous media, the components of the highly insoluble substance will be present in a bioavailable form only in minor amounts, if at all, and hence, the concentration of soluble Co2+ and Al3+ ions released is negligible.