Aluminum cobalt oxide

Toxicity to aquatic algae and cyanobacteria

Description of key information

LC50 (96 h) = 0.56 mg Co/L (Chlorella vulgaris) (read-across from cobalt chloride)
LC50 (5 d) = 0.3 mg Co/L (Ditylum brightwellii) (read-across from cobalt chloride)
NOEC (21 d) = 0.6 mg Co/L (Chlorella vulgaris) (read-across from cobalt nitrate)
Literary studies investigating the effects of aluminum in the aquatic environment have extensively used test solutions with aluminum concentrations above that of its solubility limit. Results of these studies therefore  have limited value for the investigation of intrinsic toxicity.

Additional information

No data on the toxicity to aquatic algae 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 NOEC/L(E)C10 values (expressed as Co) for aquatic algae and cyanobacteria (n=8) are summarised in the WHO CICAD, 2006 (see attached table).

Acute and chronic data for different algae species in fresh- and saltwater were extracted and used in the effects assessment. The EC50 values for freshwater algae range from 0.56 mg Co/L for Chlorella vulgaris (Rachlin and Grosso, 1993) to 10.8 mg Co/L for Spirulina platensis (WHO CICAD, 2006). Two EC50 values were available for marine species with a similar range of 0.3 mg Co/L for Ditylum brightwellii (5 d) and 10.2 mg Co/L for Nitzschia closterium for 96 h (WHO CICAD, 2006). The 21-day NOEC and LOEC values for freshwater algae ranged from 0.6 to 1.6 mg Co/L (WHO CICAD, 2006).

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

In the key study, the effects of cobalt chloride on Chlorella vulgaris were investigated in a 96 h test according to methods comparable to guidelines (Rachlin and Grosso, 1993). As a result, an EC50 of 0.56 mg Co/L was obtained.

 

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

Aluminium

The algae data from the 2009 and 2010 CIMM datasets demonstrate that elevated pH and elevated DOC are protective against aluminium toxicity, whereas hardness appeared to have a minimal effect.  The evidence of both pH and DOC effects are consistent with the Al BLM. Multiple linear regression models (MLRM) based on nominal DOC, and pH were developed to predict nominal EC10 and EC50 values for the algae dataset. The EC50 and EC10 MLRMs performed reasonably well for the dataset. The EC50 MLRM produced an adjusted R²of 0.747, and the EC10 MLRM produce an adjusted R²of 0.987 (see Figures 7.1.1.3-2, and 7.1.1.3-3, respectively).

Literature Review: Six chronic toxicity studies to a freshwater microalga (Pseudokirchneriella subcapitata) were identified in the literature as Klimisch 1 or 2 studies. Additional algal studies with Pseudokirchnerella subcapitata were performed at CIMM to evaluate acute and chronic toxicity to algae and for evaluation of water chemistry effects for modelling purposes. All endpoints from CIMM (2009; 2010a) were reported on the basis of nominal Al concentrations because total Al was not measured in these studies. However, CIMM (2010b) compared nominal to measured total Al concentrations in an identical set of algal test solutions prepared to match all water quality conditions and nominal Al exposure concentrations as used in the previous studies (2009; 2010a). In these new test solutions, average total Al concentrations were within 10% of nominal Al concentrations. A linear regression between total and nominal Al concentrations demonstrated a strong relationship with an r²value of 0.99 (Figure 7.1.1.3 -1). Therefore, nominal Al concentrations can be considered a reliable estimator of total Al concentrations in these studies. EC_r10s 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. EC_r10s and EC_r50s ranged from 0.051 to 3.15 mg Al/L and 0.024 to 4.93 mg Al/L, respectively. Water quality data for these studies suggest a direct relationship between toxicity and pH, hardness, and DOC. Studies that experimentally manipulated water quality werre reported by CIMM 2009 and 2010a. One toxicity study to a higher plant (Lemna minor) was included (Table 8). No toxicity was observed in this study, so both NOEC and EC10 values were > 45.7 mg Al/L.

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.