Aluminum cobalt oxide

Sediment toxicity

Description of key information

LC50 (48 h) = 57 mg Co/L (Chironomus tentans) (read-across from cobalt chloride hexahydrate)

Additional information

No data on sediment toxicity 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(E)C50 values (expressed as Co) for sediment-dwelling species (n=5) are summarised in the WHO CICAD, 2006 (see attached table).

Data on five species were available for the assessment. In the key study, Chironomus tentans was tested according to APHA guidelines (Standard methods for the examination of water and waste water, 1981) in a static 48-hour test, with cobalt chloride hexahydrate as test substance (Khangarot and Ray, 1989). As a result, a LC50 value of 57 mg Co/L was obtained. For further species (Branchiura sowerbyi, Tubifex tubifex and Lumbriculus variegatus) 96 -hour LC50 values ranged from > 45 to 239 mg Co/L. The results represent worst-case conditions since the solution will naturally contain more cobalt than would be available in a sediment matrix. The most sensitive value, however not conducted on a standard species, was derived from tests with the mayfly Ephemerella subvaria, resulting in a 96-hour LC50 of 16 mg Co/L (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 informationabout 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.