Munching on uranium

Rizlan Bernier-Latmani is studying how the natural appetites of bacteria can help prevent groundwater contamination.

Until about one year ago, the nuclear power industry had the wind in its sails, thanks to increasing global energy consumption and public support for carbon neutral power generation. Then came Fukushima. Almost overnight, the future of nuclear energy became less certain – Switzerland and Germany, for example, have decided to abandon it altogether. Nonetheless, the demand for uranium is not expected to decrease; the United States recently approved funding for two new nuclear reactors. Additionally, numerous nuclear power plants are planned in Asia and Eastern Europe.

Uranium is a naturally occurring radioactive element that can be found in low concentrations throughout the earth’s crust, primarily as uraninite ore. This uraninite ore is mined and processed, yielding oxidized uranium, which is water soluble – and extremely toxic. If it is released into the environment, it can easily reach the groundwater, contaminating drinking water and ultimately rivers. What strategies could be applied near uranium former mining and milling sites to keep the contaminant from reaching the groundwater?

“You can’t degrade a metal or a radionuclide per se, but what you can do is transform it into something that isn’t very soluble,” explains Professor Rizlan Bernier-Latmani, head of EN AC’s Environmental Microbiology Laboratory. And nature already appears to have found a way to accomplish this. It turns out that various bacteria process uranium while carrying out their metabolism. In so doing, they transform the soluble uranium into tiny insoluble uraninite nanoparticles. So how do we get the bacteria close enough to the uranium to process it? That’s the easy part: they’re already there!

Just like our bodies, the earth’s subsurface is teeming with bacteria. These microbial communities spend much of their time underground in a dormant state. With the right kind of “food,” bacteria could be forced into an active state, where, through their own metabolism, they would immobilize the uranium by transforming it into insoluble uraninite, keeping it far away from groundwater and people. Problem solved – or at least so it seemed.

“We started studying these uraninite nano-particles, in particular their stability to oxidation, which is what you want to avoid, but then we realized that uraninite was not the only product that was being formed,” explains Bernier-Latmani. In fact, the majority of the uranium was taking an alternate route through the bacterial metabolism. Instead of being efficiently immobilized underground in the form of tiny insoluble nano-particles, the uranium somehow wound up dangling off hair-like strands that stick out of the bacteria like tentacles. The bad news is that this compound is much more reactive than uraninite, increasing its chances of entering the water cycle.

What exactly is this new compound and where is it coming from? “We don’t know exactly what causes its formation, because theoretically, according to thermodynamics, uraninite should form,” says Bernier-Latmani. Changes in small parameters, such as the exact composition of the microbial population, the soil, or the groundwater, might be playing an important role in the process. To capture these elusive details, Bernier-Latmani’s team has taken the research out of the lab to a former uranium milling site. There they can capture all of the natural variability that occurs in the “real world,” but is easily lost in lab experiments.

Understanding how the bacteria metabolize uranium requires expertise in chemistry, microbiology and environmental engineering, a combination matched perfectly by Bernier-Latmani and her team. And this understanding could help them solve the problem of directing the bacterias’ behavior. “Ideally,” says Bernier-Latmani, “we would find a way to control which product is formed to make sure insoluble uraninite nano-particles are formed immediately.”