Aluminum cobalt oxide

Toxicity to microorganisms

Description of key information

IC50 (9 h) = 50 mg Co/L (Tetrahymena pyriformis) for growth inhibition (read-across from cobalt chloride)

Additional information

No data on the toxicity to microorganisms 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 single-species toxicity tests resulting in high quality L(I)C50 values (expressed as Co) for microorganisms are summarised in the WHO CICAD, 2006 (see attached table).

In the key study, the effects of cobalt chloride on the protozoan Tetrahymena pyiformis in a 9 hour flask test were investigated (Sauvant et al., 1995). The IC50 (9 h) for growth inhibition was 50 mg Co/L.

Another study on the ciliate Spirostomum ambiguum showed a LC50 (24 h) value of 11.8 mg Co/L using cobalt nitrate as salt. (WHO CICAD, 2006).

 

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

Aluminium

One activated sludge respiration inhibition test is available with a soluble aluminium salt, aluminium chloride (study not reported in detail). This test was performed with aluminum chloride (CAS 7446-70-0) according to a standard guideline. Domestic activated sludge was used, and the test was static. No effects were seen up to the highest test concentration of 1000 mg/L test material. The test substance contained 20 g Al/100 g and the test concentrations can be converted to mg/L Al. 1000 mg/L test material is equal to 200 mg/L Al, thus an EC10 (180 min) > 200 mg Al/L can be stated.

Aluminium is amongst the most common elements in the earth’s crust and can be found in great abundance in both the terrestrial and sediment environments. The relative contributions of anthropogenic aluminium to the existing natural pools of aluminium in soils and sediments is therefore not relevant either in terms of added amounts or in terms of toxicity. Based on these exposure considerations additional sediment and/or soil testing is not warranted. More information about exposure based waiving for aluminium in soil and sediments can be found in attached document (White paper on exposure based waiving for Fe and Al in soils and sediments final 15-03-2010. pdf).

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.