Tuesday, March 21, 2023
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Healing the Planet with Hemp

We Talk to Experts in the Cannabis Field


Cannabis is an amazing plant that can do much more for the world than just get some folks high. Researchers are finding that hemp can actually absorb harmful elements from damaged soil. We spoke with Hanah Rheay, a graduate research assistant at the Department of Chemical and Materials Engineering at New Mexico State University, about her research in the area.

The Paper.: Can you explain phytoremediation?

Rheay: Phytoremediation is basically using plants to remove toxins or contaminants from the soil. The plants have a bunch of different mechanisms for doing this. They can just take it up through their roots and move it to the plant. They can volatilize it from their leaves, even. Sometimes they change the form of the contaminant to make it more stable in the soil.

Why is it necessary to do that?

We are running out of soil—or out of clean soil, or more usable land, since we use so much for agriculture already and so much for mining and different degradation processes. For New Mexico it’s particularly important. We were working on a project for uranium phytoremediation. And in New Mexico—and really the whole western United States—there’s over 500 abandoned uranium mines. There’s particularly a lot on Navajo Nation. Uranium has a really, really, really long half-life—over 4 billion years.

All of the stuff that we mined out of the soil, we just dumped on top, and all of that area is just unusable. If we want to be able to combat some of these climate change issues or plant more trees, we have to be able to reclaim this space.

Can you talk about your research into hemp’s phytoremediation abilities?

Hemp has been really well known—historically and anecdotally—as being able to take toxins out of the soil. It’s been shown to take lots of heavy metals like lead and copper and remove it. One of the most well-known stories is that they even planted hemp at Chernobyl after that whole incident to work on phytoremediation there.

The project that we were working on was particularly focused on oilseed plants. Because one of the biggest issues with phytomediation is that if the plants take up these contaminants, then you can’t really use the plant for anything; and it’s really hard to make any money off of these types of endeavors.

So my thought was that if we look at oilseed plants, maybe we can make some sort of biofuel or industrial product that can be used on site for these operations, so at least something gets made out of the plant. Hemp is an oilseed plant and was one of the plants that we tried in this project.

Our hypothesis was that the contaminant—uranium in this case—would not go into the oil but would go into the other parts of the plant, and we could still salvage that oil with little contamination and then use that further.

And we did have success on that front. There is a fraction of the contaminant that went into the seed. But when we pressed the seed, almost all of it remained in the seed meal, not the oil. Out of the plants that we tested, hemp was one of the best, if not the best, phytoremediator—meaning that it took up the most amount of contaminants from the soil over the same period of time as another plant. We tested it against sunflower and canola and other plants like that.

What about the other parts of the plant? Are those still usable?

Probably not. There was a fair amount of contamination in the flower and the stalks. And that was something that we expected. So for that, what we do is we end up just burning it all and concentrating it into a little pile of ash. It’s easier to dispose of a little bit of ash rather than a bunch of soil.

Do the plants become irradiated enough that they’re dangerous to handle?

Not that much. I mean, we do have some pretty heavy safety restrictions, being at universities, but they weren’t super dangerous to handle. We still took all the safety precautions, especially with the uranium. Uranium is really only dangerous or toxic if you ingested or inhale it. And that’s one of the reasons you want to remediate the soil, especially here, because all the dust is blowing around and you inhale that dust, and that’s actually how uranium becomes toxic to you. That’s because uranium is an alpha emitter, and alpha particles don’t penetrate clothes. But once they’re in your body, they’re very unsafe.

I imagine that there are areas of New Mexico that could specifically benefit from phytoremediation.

Yes. The Four Corners region is where we were doing this work. We actually got the soil from one of these abandoned mine sites. The EPA started a Superfund to clean up these abandoned uranium mines, and they identified around 50 "priority" mines. Most of these are in the northwest corner of New Mexico—the Four Corners region—around Grants and Gallup and Shiprock.

Is the soil fully usable again after phytoremediation?

Well, that’s one thing that’s undetermined. The EPA has certain guidelines, and the goal is to clean up the top 15 centimeters of the soil, and I think that’s mostly just to mitigate the risks. The thing is that these would be very long-term, ongoing projects—like on the order of centuries. The soil is being used for some sort of production, but rather than production that you can capitalize on, you’re just focusing on the remediation. That’s why a lot of this doesn’t ever get done. No one really makes any money off of it.


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