Investigating the environmental impact of rare-earth metals

In 5 seconds An UdeM research team has found that metals like lanthanum, cerium and yttrium used in high-tech products compete with each other in aquatic organisms, mitigating their biological effects.

In an increasingly connected world, rare-earth metals with odd names such as lanthanum, cerium and yttrium have become strategic assets. They are used in everything from mobile phones to wind turbines to electric vehicles. Currently, they are at the centre of a trade war between the U.S. and China.

However, scientists are concerned about these metals for reasons unrelated to international political tensions. What do we really know about the environmental impact of their extraction?

Kevin Wilkinson, a professor in Université de Montréal’s Department of Chemistry, along with his students Laurianne Pagé and Marie-Hélène Brunet, is trying to find out. Their research on the complex interactions between rare-earth metals and aquatic organisms has uncovered mechanisms that could change the way we assess the environmental risks.

Their results are published in the journal Environmental Pollution.

Geopolitics enter the laboratory

Kevin Wilkinson

“(U.S. President Donald) Trump wants lanthanum, cerium and yttrium, but China controls nearly 80 per cent of global production and recently halted exports to the United States, prompting North America to reexamine the viability of its own sources, many of which are in Canada,” said Wilkinson.

The Nechalacho mine near Yellowknife in the Northwest Territories is currently one of the most advanced extraction projects. Other deposits of the valuable metals have been found in Quebec.

In collaboration with Environment and Climate Change Canada, the UdeM researchers focused on lanthanum, cerium and yttrium and their interactions with Chlamydomonas reinhardtii, a microscopic alga often used to investigate the mechanisms by which metals are absorbed by living organisms.

“We’ve been using this alga in our lab for more than 20 years,” Wilkinson explained. “It's one of the first algae whose genome has been fully sequenced, which enables us to understand its molecular mechanisms when exposed to metals.”

Competition good for the environment

The laboratory tests produced counter-intuitive results: the presence of several rare-earth elements does not increase their bioaccumulation in contact with Chlamydomonas reinhardtii. On the contrary, they compete for cellular uptake, reducing the absorption of each.

“We don’t expect toxicity to add up to the sum of the metals,” Wilkinson explained. “Mixing these metals has a beneficial effect rather than an additive one. The worst outcome would have been for two contaminants to have the sum of their effects on the organism, but this is not the case here.”

Hard water: a natural shield

As strategic metal mining intensifies in Canada, the project led by Kevin Wilkinson and his team is part of a coordinated effort by several Canadian teams.

The research team also discovered that the ions naturally present in water that determine its “hardness,” such as calcium and magnesium, provide protection against the absorption of the metals.

Experiments have shown that even moderate concentrations of calcium can significantly reduce the uptake of these metals by an organism. In natural environments near mines, where the ratio of calcium to rare metals can be as high as 10,000 or 100,000 to 1, this protective effect is crucial.

“In Quebec, our freshwater contains little calcium and magnesium, so there is less of a protective effect,” said Wilkinson. “We did see this effect in the past, when the province was more affected by acid rain than the United States was.”

Regions with soft water, such as Quebec and Scandinavia, are therefore at greater risk of pollution from rare-earth metal extraction than areas with harder water.

Other elements released

To extract rare-earth metals, the rocks containing the elements are crushed. This increases the contact surface area, making it possible to recover the desired metals, but also releases all the other elements present in the rock.

The waste produced by this process therefore contains a variety of contaminants and could increase their concentration in nature as the exploitation of rare-earth metals intensifies in Canada. Wilkinson’s project is part of a coordinated national effort to investigate the impacts, involving several research teams.

While his team studies uptake mechanisms, UdeM biology professor Marc Amyot is studying how the contaminants move up the food chain, and in Ontario researchers are examining the toxicity of rare earths.

“In the lab, we control everything,” said Wilkinson. “In the field, it’s more difficult but more realistic, with lower concentrations. Basic research and field studies complement each other and together will give us a better understanding of the environmental issues involved in exploiting these strategic metals.

"Currently, our team is observing contamination by these metals following the recycling of electronic products. There’s no miracle solution. The energy transition requires these metals for green technologies, so we need to understand their environmental impact to avoid solving one ecological problem by creating another.”

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