Researcher Danielle Stevenson digs up California buckwheat grown at a brownfield site in Los Angeles.

Researcher Danielle Stevenson digs up California buckwheat grown at a brownfield site in Los Angeles. Patrick T. Fallon / AFP via Getty Images


Turning Brownfields to Blooming Meadows, With the Help of Fungi

Toxicologist Danielle Stevenson cleans up carbon-based pollutants and heavy metals from contaminated sites using fungi and plants. She’s also training environmental justice and tribal communities in using these methods so they can remediate toxic sites on their own.

The United States is dotted with up to a million brownfields — industrial and commercial properties polluted with hazardous substances. These sites are disproportionally concentrated near low-income communities and communities of color, according to the Environmental Protection Agency, and researchers predict that heavy rains and flooding due to climate change are likely to both spread and increase exposure to these contaminants.

For more than 15 years, Danielle Stevenson, who holds a PhD in environmental toxicology from the University of California, Riverside, has been pioneering a nature-based technique for restoring contaminated land, using fungi and native plants to break down toxins like petroleum, plastics, and pesticides into less toxic chemicals.

The usual way of dealing with tainted soil is to dig it up and cart it off to distant landfills. But that method is expensive and simply moves the problem somewhere else, Stevenson says in an interview with Yale Environment 360, “typically to another state with less restrictive dumping laws.”

In a recent pilot project funded by the city of Los Angeles, Stevenson, 37, working with a team of UC Riverside students and other volunteers, significantly reduced petrochemical pollutants and heavy metals at an abandoned railyard and other industrial sites in Los Angeles. While her research is still in its early stages, Stevenson says she believes her bioremediation methods can be scaled up to clean polluted landscapes worldwide.

California buckwheat that has absorbed lead at a contaminated site in Los Angeles.

California buckwheat that has absorbed lead at a contaminated site in Los Angeles. Patrick T. Fallon / AFP via Getty Images

Yale Environment 360: I understand that you grew up on the shores of Lake Erie in a highly polluted area.

Danielle Stevenson: The Cuyahoga River, near Lake Erie, used to catch on fire from oil spills. There’s a huge amount of industrial agricultural runoff that leads to toxic algae blooms. The second-largest floating plastic island of the Great Lakes is in Lake Erie.

But I was surprised to see abandoned oil refineries and factories with trees, plants, and mushrooms growing. I mean, they’ve found fungi growing in Chernobyl in a melted down nuclear reactor. I’ve been on sites that look so desolate and bleak, where the air smells like diesel. It looks like nothing could possibly live there. But when we sample the soil, we always find life, and we especially find fungi that are really resilient and have found a way to live in those conditions and get some sort of food from the pollution.

e360: So you became interested in fungi, eventually founding your own mycoremediation company, D.I.Y. Fungi. What are fungi?

Stevenson: They are their own kingdom of life. They are not bacteria, not a type of plant or animal. Some fungi form mushrooms [as their fruiting bodies], like the ones we like to eat. Other fungi do not form mushrooms but create these beautiful dynamic networks throughout forests and grasslands that connect to the roots of plants. Fungi are largely overlooked, but it is a really important kingdom without which we wouldn’t have soil or the carbon cycle or so many other really important functions in our ecosystems.

“In three months we saw a more than 50 percent reduction in all pollutants. By 12 months, they were pretty much not detectable.”

e360: How do fungi help restore contaminated soil?

Stevenson: Decomposer fungi can degrade petrochemicals the same way they would break down a dead tree. And in doing so, they reduce the toxicity of these petrochemicals and create soil that no longer has these contaminants or has much reduced concentrations of it. They can also eat plastic and other things made out of oil, like agrochemicals.

e360: They’re not picky eaters.

Stevenson: They would probably rather eat cellulose, which is what plants are made of. But if there isn’t any cellulose, and instead there’s diesel or something that’s essentially made out of carbon, they will find a way to eat it, applying their enzymes the same way they would if it was cellulose.

e360: You worked at industrial sites in Los Angeles that were highly contaminated with heavy metals: How did the fungus help there?

Stevenson: Unfortunately, most metals don’t break down because they’re not carbon-based. In nature, it’s actually plants that pull metals out of soil. And so there are fungi, they’re called arbuscular mycorrhizal fungi, that can help plants do that better. And so on Taylor Yard [the Los Angeles railyard] and other sites, I’ve worked with a combination of decomposer fungi, arbuscular mycorrhizal fungi, and plants that we previously found to be able to pull metals like lead and arsenic out of the soil into their aboveground parts. These plants can then be removed from the site without having to remove all of that contaminated soil.

Mushrooms growing at a brownfield site in Los Angeles.

Mushrooms growing at a brownfield site in Los Angeles. Danielle Stevenson

e360: How did the sites look different after the work that you did on them?

Stevenson: They became basically beautiful meadows of native plants that were flowering, and now there are bees and birds and all sorts of life coming through. We had a very high success rate. In three months we saw a more than 50 percent reduction in all [petrochemical] pollutants. And then by the 12-month period, they were pretty much not detectable.

e360: On these sites, you grew native plants that took up a fair amount of the lead and other metals that had contaminated the soil. But then the plants themselves become toxic, right? Do you just leave them there on site?

Stevenson: No, you harvest them. You take a huge amount of biomass that contains these metals and either reduce it to a small amount of ash, through incineration, or sludge that contains concentrated metals, which can then be disposed of as hazardous waste or even reused. In some cases, you could extract the precious metals and use them in batteries and electronics.

e360: The usual way of dealing with toxic soil— called “dig and dump”— is to excavate it and move it elsewhere. Why is that not the best option?

Stevenson: It’s expensive. It costs millions of millions of dollars per site. And because of that, contaminated sites sit all over the country for decades not being cleaned up. Furthermore, it doesn’t solve the problem, it just moves it somewhere else, typically to another state with less restrictive dumping laws. It spreads a ton of toxic dust along its route, and [all that trucking] leads to emissions contributing to climate change.

“People who live in a place impacted by pollution need to have a say in how their neighborhood is being cleaned up.”

e360: You don’t just work with polluted soil. You were invited into a bicycle shop to help them deal with their waste lubricant. How did that go?

Stevenson: They showed me a massive pile of garbage bags filled with lubricant-soaked rags that all get sent to the landfill. Bike lubricants are made of petrochemicals, [including] one of the forever chemicals, Teflon, the same stuff that’s in pans. So it’s super toxic and sticks around forever.

I inoculated mushroom spawn into these lubricant-soaked rags. The rags themselves were often made out of some type of plant fiber or plastic-type fiber, like polyester. So I knew that all of those were things that the fungi could eat as well, and I basically layered them in with cardboard from the bike shop. Later, I added worms that would continue the process of breakdown by taking what was essentially a mycelium block that had grown on the rags and then turning that into soil.

e360: So this pilot project was a two-step process: You begin with the mycelium, which start the digestion, and the worms complete it. Is this something that other bike shops could start doing themselves?

Stevenson: I’m actually working with this really awesome bike shop in L.A. now. I just need some funding to actually test that system. I have a whole design that’s had many iterations and is greatly improved. It would be so cool.

Stevenson at a Los Angeles cleanup site.

Stevenson at a Los Angeles cleanup site. Patrick T. Fallon / AFP via Getty Images

e360: You’ve said that using fungi and plants to treat contamination is so much cheaper than other ways of dealing with the problem. So why aren’t we doing more of it? Is it that we just don’t know enough yet?

Stevenson: There have been scaling issues, which is why I’ve been working with academia, as well as with industry, regulatory agencies, and governments on scaling. There’s a lot of regulatory barriers and even funding barriers to testing some of these so-called newer methods.

e360: I understand that you also run training programs with Native people so that they can start doing this restoration work themselves [on tribal lands], without calling in outsiders, and you work with youth programs and environmental justice communities to empower them to clean up their own communities.

Stevenson: There have been a number of sacred sites that I have worked on at the invitation of several tribes that wanted to explore bioremediation. What I have been told is that a lot of times [these communities] haven’t felt listened to. And then I come in with the science that basically backs up the knowledge that the people already have — affirming the power of nature to restore itself. I’m saying the same thing they are, except I’m using the scientific language that regulatory agencies and other groups are more likely to listen to.

People who live in a place impacted by pollution need to have a say in how their neighborhood is being cleaned up. We need to empower them with the tools to do this. That’s why along with doing these studies and pilot projects, I’ve been running workforce development programs. Potentially, they could bring economic opportunities and benefits to the community in addition to cleaning up the contaminated site.

This interview was edited for length and clarity.