Aluminum cobalt oxide

Toxicity to terrestrial arthropods

Description of key information

NOEC (28 d, mortality) = 100 mg Co/kg soil dw (Folsomia candida) (read-across from cobalt chloride hexahydrate)

Additional information

No data on the toxicity to terrestrial arthropods 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 soil-dwelling invertebrates resulting in high quality EC50/NOEC values (expressed as Co) are summarized in the WHO CICAD (2006).

The only study on an arthopod species, the springtail Folsomia candida, was conducted with cobalt chloride hexahydrate according to ISO-Guideline 11267 on two different soils (artifical soil according to OECD 207 and standardised field soil LUFA 2.2) by Lock et al. (2004). The more sensitive 28-day NOEC of 100 mg Co/kg soil dw was measured on standardised field soil (pH CaCl2 5.49) while on artificial soil with a pH(CaCl2) of 7.14, the 28-day NOEC was found to be 1000 mg Co/kg soil dw. Cation exchange capacity and pH are indicated as main factors influencing cobalt bioavailability.

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

Aluminium

Aluminium, aluminium powders and aluminium oxide are non hazardous (not classified for the environment). Aluminum (Al) is the most commonly occurring metallic element, comprising eight percent of the earth's crust (Press and Siever, 1974) and is therefore found in great abundance in both the terrestrial and sediment environments. Concentrations of 3-8% (30,000-80,000 ppm) are not uncommon. The relative contributions of anthropogenic aluminium to the existing natural pools of aluminium in soils and sediments is very small and 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 waiving for secondary poisoning for Fe and Al compounds final report 25-01-2010. doc).

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.