How Rare Earth Metals Compete in Contaminated Waters

Global demand for rare earth elements (REE) is accelerating—driven by everything from wind turbines to smartphones. Understanding how these metals behave in the environment is becoming urgent. Recent research using the freshwater green algae Chlamydomonas reinhardtii reveals that several common REEs, including lanthanum, cerium, and yttrium, enter aquatic organisms through a single shared uptake mechanism. This discovery reshapes current thinking on toxicity and risk modeling for environments impacted by REE extraction and waste.

The study found that these rare earth metals don’t act on their own. Instead, they use the same entry point to get into algae cells, essentially competing with each other. They were taken up by the algae at almost identical rates, showing they behave in similar ways. The strength of their attachment to the cells was also nearly the same, meaning their effects in the environment are closely linked and shouldn’t be assessed separately.

For environmental consultants and regulators, the key takeaway is that additive models of toxicity may overstate the risks when multiple REEs are present together. In real-world mining scenarios, the competitive behavior of these metals may lead to lower-than-expected toxicity, highlighting the need for more nuanced risk assessment models.

Water Hardness Can Diminish REE Toxicity

Another critical finding from the study is the role of natural water chemistry in moderating REE bioavailability. Ions like calcium and magnesium—commonly found in freshwater systems—can outcompete REEs for the same biological uptake sites, especially when present at millimolar concentrations.

In lab tests, even small amounts of calcium in the water were enough to block rare earth metals from being absorbed by algae—especially when metal levels were low. Real-world water samples near the Nechalacho mine in Canada showed similar conditions, with calcium levels high enough to offer this kind of protection.

Here’s why it works: calcium and magnesium don’t stick as strongly to the algae as rare earth metals do, but they’re usually found in much higher amounts. That lets them crowd out the metals and reduce their impact. For mine operators or water treatment facilities, this means keeping natural minerals like calcium in the water could be a simple, affordable way to lower the risk of metal pollution.

The broader implication is that conventional environmental models may need to account not only for metal concentration but also for the competitive dynamics of mixed contaminants. Biotic ligand models (BLMs), which incorporate both metal interactions and water chemistry, offer a promising alternative. These models could enable more accurate and cost-efficient assessments of REE impact—particularly in complex environments with multiple metal sources.