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Ecotoxicological information

Long-term toxicity to aquatic invertebrates

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Description of key information

NOEC (28 d) = 0.03 mg Co/L for Daphnia magna (reproduction) (read-across from cobalt sulfate)

Key value for chemical safety assessment

Additional information

No data on the long-term toxicity to aquatic invertebrates 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 chronic single-species toxicity tests resulting in high quality NOEC/L(E)C10 values (expressed as Co) for freshwater invertebrates (n=4) are summarised in the WHO CICAD, 2006 (see attached table).

Chronic data for two different species were extracted and used in the effects assessment. The 21-day LC50 values (mortality) for Daphnia magna range from 21 μg Co/L, tested as cobalt chloride hexahydrate (Biesinger & Christensen, 1972) to 30 μg Co/L, tested as cobalt sulfate (WHO CICAD, 2006).

More sensitive values were available as NOEC values (reproduction) for Daphnia magna (21 d and 28 d) and Ceriodaphnia dubia (7 d), and ranged from < 3 to 13 for C. dubia (unknown cobalt compound) and 30 to 50 µg Co/L for D. magna (unknown cobalt compound), respectively. The lowest NOEC(28 d) of 3 µg Co/L was obtained in a study conducted with cobalt sulfate on D. magna (Kimball, 1978, cited in WHO CICAD, 2006). Out of these results, the NOEC value of 30 µg Co/L originating from a recent high quality study with varying levels of calcium carbonate (Nagpal, 2004, cited in WHO CICAD, 2006) was considered as most reliable and relevant effect value on a standard test organism and hence, was selected as Environmental Reference Value (ERV) for classification purposes.

In the reported key study conducted according to methods comparable to guidelines, the effects of cobalt chloride hexahydrate on Daphnia magna were investigated and resulted in an EC50 (28 d) of 12 µg Co/L for reproduction and a respective LC50 (28 d) of 21 µg/ Co/L (Biesinger & Christensen, 1972).

Further results for other aquatic invertebrates are available and comprised in the attached table.

 

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

Aluminium

Literature Review: Six long-term chronic toxicity studies to two species of aquatic invertebrates (Ceriodaphnia dubia and Daphnia magna) were identified as acceptable studies. ECr10s were calculated using raw data provided from each study using the statistical program Toxicity Relationship Analysis Program (TRAP) version 1.10 from the US EPA National Health an Environmental Effects Research Laboratory (NHEERL). All other endpoints were as reported in each study. NOECs and EC10s ranged from 0.076 to 4.9 mg Al/L and 0.021 to 0.997 mg Al/L, respectively. Water quality data for these studies suggest a direct relationship between toxicity and pH, hardness, and DOC. For studies that experimentally manipulated water quality (e.g., CIMM 2009 and 2010a ), toxicity decreased with increasing pH, hardness, and DOC.

Recent studies conducted by the Chilean Mining and Metallurgy Research Center (CIMM) tested aluminium toxicity to C. dubia and D. magna (one data point) across a range of pH, DOC, and hardness values. These results demonstrated that increasing DOC concentration has a protective effect on aluminium LC50s for invertebrates. Increasing water hardness also had a protective effect. Aluminium toxicity was reduced at high pH, but a larger reduction was observed when changing pH from 6 to 7 than from 7 to 8. 

The acute fish BLM developed for S. salar was applied to the chronic invertebrate data (CIMM 2009, CIMM 2010; Figure 7.1.1.2.2.-1) by developing a critical accumulation value appropriate for this organism. In addition, the chronic invertebrate data suggested that overall fit would be improved with a small increase in the Ca binding parameter (i.e. the log K for Ca binding at the biotic ligand was increased from 4.2 to 4.8), which is the same adjusted value used in the chronic fish model. After application of the modified Al BLM, the variability in the response curve data substantially decreased (Figure 7.1.1.2.2.-2). These data were subsequently used to establish the CA10 (i.e. the critical accumulation level that results in a 10% reduction in reproduction), and likewise, the CA50. The CA10 and CA50 values can then be used to predict EC10 values and EC50 values in various water types.  

Figures 7.1.1.2.2.-3 and 7.1.1.2.2.-4 provide an evaluation of the ability of the chronic invertebrate Al BLM to predict EC50 and EC10 values. All of the EC50 values are predicted within 2-fold of the reported EC50 values. Most of the EC10 values are predicted within 2-fold of the reported EC10 values, and all of the predicted EC10 values are within 4-fold of the reported values. These results indicate that the chronic Al BLM performs reasonably well for predicting sublethal effects of Al on invertebrates. It should be noted that in both the fish and the invertebrate tests, saturation index calculations suggested that the majority of the toxicity values exceed Al(OH)3solubility. However, bioavailability factors (i. e. pH, DOC, and hardness) still are consistent with the trends predicted by the Al BLM.

Two additional LC50 values that are not included in this comparison were reported for pH 7 and pH 8 in filtered test media (i. e., filtered before organisms were exposed). The filtered test media were approximately 5-fold less toxic, meaning that their LC50s were approximately 5-fold higher than the results from exposure to unfiltered media. Therefore, toxicity was largely a function of exposure to aluminium hydroxides, which are removed by filtration through these types of filters.

 

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.