Aluminum cobalt oxide

Endpoint summary

Additional information

No data on bioaccumulation 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

Information taken from Environment Canada (2011):

Cobalt is essential in small amounts for nitrogen fixation by bacteria, blue-green algae, and symbiotic systems such as those in the root of leguminous plants. It is also an essential micro-nutrient element for animals and is required for the formation of vitamin B12 and for its participation in enzymatic processes (Environment Canada, 2011).

Bioaccumulation of metals - like that of organic substances - is of potential concern because of the possibility of chronic toxicity to the organisms accumulating these substances in their tissues and the possibility of toxicity to predators eating these organisms. Bioaccumulation potential is typically quantified by determining either a bioaccumulation factor (BAF), or a bioconcentration factor (BCF). However, these ratios are currently the object of criticism when applied to metals because they are considered of little usefulness in predicting metal hazards. For example, some metals may naturally be highly accumulated from the surrounding medium because of their nutritional essentiality. Furthermore, both essential and non-essential metals may be regulated within relatively narrow margins by the homeostatic and detoxification mechanisms that many organisms possess. It follows that when ambient concentrations of metals are low, BCFs and BAFs are often elevated. Conversely, when ambient metal concentrations are high, BCFs and BAFs tend to decrease. Thus, inverse relationships may be observed between BCF and BAF values and metal exposure concentrations, and this complicates the interpretation of BCF/BAF values. Natural background concentrations in organisms may contribute to these negative trends. In addition, inverse relationships can occur for non-essential elements as well because there are a finite number of binding sites for these metals within an organism that could become saturated at higher concentrations (Environment Canada, 2011).

 

There are several lines of evidence to suggest that the bioaccumulation potential of cobalt in natural ecosystems is relatively low. First of all, low BAFs have been reported in eight laboratory (steady state) studies and four field studies; five BSAF-sediment values have been found to be well below 1; and, four (out of four) average BSAF-soil values have been reported to be well below 1. In addition, results from six field investigations plus two laboratory studies indicate the absence of biomagnification of cobalt in natural food webs. Finally, cobalt is an essential micro-nutrient, the uptake of which is expected to be regulated to some extent by many organisms (Environment Canada, 2011).

References:

Environment Canada. Health Canada (2011). Screening Assessment for the Challenge. Cobalt, cobalt chloride, cobalt sulfate

Aluminium

In general, metals do not biomagnify unless they are present as, or having the potential to be, in an organic form (e.g. methylmercury). Organometals tend to be lipid soluble, are not metabolized, and are efficiently assimilated upon dietborne exposure.The available evidence shows the absence of aluminium biomagnification acrosstrophic levels both in the aquatic and terrestrial food chains. The existing information suggests not only that aluminium does not biomagnify, but rather that it tends to exhibit biodilution at higher trophic levels in the food chain. More detailed information can be found in the attached document (White paper on waiving for secondary poisoning for Al & Fe compounds final report 02-02-2010. pdf). BCFs for Aluminium can be found to range from quite low (~100) to quite high values (11,000), see attached pdf: White paper for waiving secondary poisoning for iron and Aluminium. This variance can in large part be explained by the difference in exposure conditions for the various studies. The inverse relationship between water and BCF/BAF values limits the ability to describe hazard as a result of the size of the BCF, i.e., the most pristine ecosystems have the highest BCFs. A better approach is to directly assess the concentrations of Al at various trophic levels in the ecosystem. 

Herrmann and Frick (1995) studied the accumulation of aluminium at low pH conditions in benthic invertebrates with time and representing different functional feeding groups (predators and detritus feeders). Invertebrates of different taxa and feeding type were collected in springtime, when acidity and A1 levels mostly increase from seven streams in southern Sweden. Four of the streams typically had pH values of 4 - 4.5 and contained 0.40 - 0.70 mg inorganic A1/L. The other three streams showed pH values around 6 and A1 concentrations of 0.05 mg inorganic A1/l. For most taxa that could be compared, the animals from the most acidic streams (pH 4) contained more A1 than those from the less acid streams (pH 6). At both pH levels there was a clear tendency that predators contained significantly less amounts of aluminium than shredders. The latter results do not support the hypothesis that aluminium can be accumulated along a food chain in an acidic environment.