Aluminum cobalt oxide

Toxicity to soil macroorganisms except arthropods

Description of key information

NOEC (24 weeks) >= 92 mg Co/kg soil dw  (Eisenia fetida) for growth (read-across from cobalt chloride hexahydrate)

Additional information

No data on the toxicity to soil macroorganisms 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 macroorganism (non-arthopod) toxicity tests resulting in high quality EC50 values (expressed as Co) for Eisenia fetida and a nematode species (n=4) are summarised in the WHO CICAD (2006).

No EC50 values are available for any of the three studies on Eisenia fetida. The results range from a NOEC (growth, 8 weeks) of 30 mg Co/kg soil dry weight, tested as unspecified cobalt salt (with significant differences to the control from 300 mg/kg soil dw) to 77% mortality at 4720 mg Co/kg soil dry weight, tested as cobalt chloride (hydration not specified) after 10 weeks exposure (WHO CICAD, 2006).

The key study for effects on growth reports a NOEC of >=92 mg Co/kg soil dry weight after 24 weeks exposure to cobalt chloride hexahydrate (Neuhauser et al., 1984).

Another study on the nematode species Caenorhabditis elegans reports 24 hour LC40 values for total cobalt of 1274 mg/L and for the free ion at 1210 mg/L (Hartenstein et al., 1981; WHO CICAD, 2006).

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 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.