Cobalt(2+) hydrogen citrate

Endpoint summary

Additional information

No data for bioaccumulation are available for cobalt hydrogen citrate. However, there are reliable data available for different analogue test substances and for cobalt measured as element in field investigations, respectively.

The environmental fate pathways and ecotoxicity effects assessments for cobalt metal and cobalt compounds is based on the observation that adverse effects to aquatic, soil- and sediment-dwelling organisms are a consequence of exposure to the bioavailable cobalt ion, released by the parent compound. The result of this assumption is that the ecotoxicology will be similar for all soluble cobalt substances used in the ecotoxicity tests. Therefore, data from soluble cobalt substances are used for the derivation of ecotoxicological and environmental fate endpoints, based on the cobalt ion. With respect to these considerations, data collected on elemental cobalt (e.g. environmental concentrations for Co2+) can also be taken into account.

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