Testing of rare earth element ore leachate for toxicity in aquatic organisms - Project leader, Melissa Desforges, MMS, NRCan
In aquatic toxicity testing of metals, the behaviour of the divalent metal cation - the species of metal largely considered to be the most toxic - is well understood, particularly with respect to binding with natural organic compounds. These natural organic compounds are very important in determining toxicity to aquatic life because they bind to metal cations and render then unavailable or non-toxic. The toxicity and behaviour of REE in natural environments has not been studied to any great extent, and given the trivalent charge of many REE, it is largely unknown how toxic they are to aquatic species, and how they interact with natural organic compounds.
In the CanMIN laboratories, the acute toxicity of many REE to Daphnia pulex (a species of aquatic invertebrate commonly used in aquatic toxicity research) has been assessed and therefore CanMIN has a good understanding of REE toxicity and how the species in question behaves in test systems. CanMIN will advance the understanding of the behaviour of REE in the environment by using a northern species (Daphnia middendoffiana) to provide novel information of potential risks and environmental issues in Canada’s north. Given that the effect of pH and natural organic matter (NOM) complexation of REE is largely unknown, CanMIN will manipulate the leachate by adding NOM, altering water hardness or pH to investigate what impact water chemistry has on observed toxicity.
With interest in REE mining being developed in Canada and elsewhere, this data will help identify potential risks and environmental issues associated with REE mining.