Aluminum cobalt oxide

Toxicity to aquatic plants other than algae

Description of key information

EC50 (4d) = 0.14 mg Co/L (Spirodela polyrhiza) for growth rate (read-across from cobalt chloride)

Additional information

No data on the toxicity to aquatic plants 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 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 (4 d) values of 0.14 and 0.24 mg Co/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.
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.

Aluminium

One study on the toxicity of aluminium chloride to duckweed Lemna minor is available which was conducted according to ASTM (Proposed New Standard Practice for Conducting Static Toxicity Tests with Duckweed) and resulted in a 96h-NOEC of > 45.7 mg/L (measured).

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.