Aluminum cobalt oxide

Toxicity to terrestrial plants

Description of key information

EC10 (21d) = 1 mg Co/kg soil dw (Brassica napa) for shoot biomass (read-across from cobalt chloride)
EC50 (21d) = 7 mg Co/kg soil dw (Brassica napa) for shoot biomass (read-across from cobalt chloride)

Additional information

No data on the toxicity to terrestrial 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 terrestrial plants toxicity tests resulting in high quality EC10 and EC50 values (expressed as Co) for terrestrial plants (n=3) are summarised in the WHO CICAD (2006). The key study however, is not included in this document.

This study conducted according to ISO 11269-2 (ISO 1995) investigated the toxicity of cobalt chloride to three plants in 10 different soils, with the overall lowest EC10 (21 d) value for Brassica napa of 1 mg Co/kg soil d.w. (Li et al., 2009). The range of EC10 values in the study varied from 1 mg Co/kg soil d.w. for Brassica napa and Lycopersicon esculentum to 617 mg Co/kg soil d.w. for Hordeum vulgare. The corresponding lowest EC50 was reported as 7 mg Co/kg soil d.w. Generally, a higher sensitivity to cobalt was observed in soils of lower pH. Brassica napa was the most sensitive species, followed by Lycopersicon esculentum and least sensitive was Hordeum vulgare.

Two other studies report EC20 values based on growth of Medicago sativa, Hordeum vulgare and Raphanus sativus which ranged from 0.6 to 45.2 mg Co/kg soil d.w., with citrus fruits showing no effect concentrations < 100 mg Co/kg soil d.w. (WHO CICAD, 2006).

There is little evidence of cobalt toxicity to plants due to elevated concentrations in soil. Cobalt tolerance, along with tolerance to other metals, has been found in plant populations growing on soils high in particular metals. Exclusion of the metal has been demonstrated in the cobalt tolerance of some species, whereas others growing on cobalt-rich copper clearings are hyperaccumulators of cobalt (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.