- In January of 2025, Southern California experienced one of the most devastating catastrophic wildfires in its history.

(fire roars) (sirens wailing) But what's actually perhaps more devastating is the toxic mess that it leaves behind.

All that toxic stuff that was in the house or the car gets deposited right into the soil, where it stays.

The problem is that because we don't have a good way of dealing with this polluted soil other than just digging it up and moving it somewhere else, these sites often sit for decades, not being cleaned up.

My proposal is that we work with nature-based methods like mycoremediation to clean up soil in place.

(light electro-synth music) (gentle contemplative music) My name is Danielle Stevenson, and I'm an environmental scientist that focuses on bioremediation, so cleaning up pollution with plants, fungi, and microbes.

This is the plot I did my mycoremediation study in.

So you can actually see a lot of native plants that we had planted.

Honestly, we had to replant more than four times because it was so toxic here that nothing could grow, but it's worth noting: you see plants, you don't really see the fungi, and that's because the fungi we work with for remediation do all that work underground.

So they are growing through the contaminated soil, breaking down organic contaminants, and connecting to the roots of these plants and helping them survive in the toxic soil and helping the plants take up more metals.

There've been fires here for millennia, but this one had the greatest spread of impact and loss and devastation.

So when a home or building, or car burns down, it releases all the toxic stuff into the soil.

So, for example, we build our homes out of stuff like drywall with asbestos in it, in some cases.

We have homes that were painted with lead-based paint, but in addition, when certain things get burnt, they actually can create even more toxic contaminants like dioxins and furans.

These are only really produced through fire.

Contaminants can blow into our homes as dust.

They can get into our food crops that we eat.

They can get into our drinking water, that we then would consume.

And without cleaning up all the toxic stuff left behind in the soil and water, and air after, especially an urban fire, it can just lead to so many health impacts for both the firefighters and any type of first responders, but also for people that are trying to return home and live on these sites again and in the area.

(train scraping) (light thoughtful music) (birds chirping) (gentle contemplative music) (car door slams) So this is my friend's myco art studio, and we're actually gonna head downstairs into the basement, where I have a bit of a lab going on.

(lively folk music) This is a mushroom.

All this stuff down here, this big white block, is something called mycelium, and mycelium is just the living, breathing fungus.

So when we're working with fungi for remediation, we're actually working with the living part, the mycelium.

So, the basic process of cultivating fungi to be able to use them in the field, is you collect your sample from the field, we then inoculate.

So we transfer that fungal culture onto the Petri dish and let it grow, and just keep scaling up till it's fully grown and ready to go out into the field.

So to get to a stage like this is actually maybe like three months of work.

So in the US, there's thought to be over a million contaminated sites across the country, but these are only sites that are known to the Environmental Protection Agency and regulated by them.

(tense thoughtful music) So what qualifies as a contaminated site is just a site where there's elevated concentrations of at least one type of contaminant.

So it could be lead.

Often, it's a bunch of different types of contaminants like petrochemicals and lead, and arsenic.

The most highly contaminated sites, they're called Superfund sites.

A study found that living within a few miles of a super-contaminated site is actually taking years off of our lives because contaminated dust and water from those sites ends up getting into our homes.

We end up getting exposed to it in some way.

So it's a real widespread issue across the entire country.

So remediation is working to clean up pollution in the environment.

Typically, that's done through digging up the pollution and dumping it somewhere else, and that's the most conventional means.

So in California, contaminated soil from dig-and-dump remediation is actually the largest waste stream produced here and exported.

(gentle contemplative music) You can imagine all of these trucks hauling so much soil across state lines to Utah, Arizona, or Nevada, where it is dumped on hazardous waste landfills, on tribal reserves.

And if you look at a map of just the regulated contaminated sites in the country, you'll quickly probably see that there isn't gonna be space to just dig up all the contaminated land in the country and dump it somewhere else in this country.

(laughs) And it's not really even addressing the soil; it's not cleaning it in any way.

It's just literally moving it to another location, where you end up then having to find clean soil to fill in these giant holes left behind.

Today, we are getting some different types of fungi growing so that we can apply them in the field at the post-fire site in Altadena.

So I use this type of fungus when soils or sites have metals like lead or arsenic in them.

And that's because for those sites, we typically need to work with plants to pull those metals out of the ground and clean the site.

But plants on their own can sometimes struggle to grow in a site that's super toxic.

And these fungi that are called arbuscular mycorrhizal fungi, you know, it's a big mouthful, but they are plant symbionts.

So they connect to almost all plants on Earth in every ecosystem and trade with plants to help them grow.

So the plant and the fungus benefit from the relationship, and they give each other what they need.

What I've seen in my own research is that they help plants survive in remediation sites where they wouldn't survive otherwise.

So to cultivate these fungi, you have to collect their spores, and then you basically grow plants in pots.

It's the same kind of process where you start with a small amount of spores from these AMF, and you end up with as many pots as you grow.

So it's a similar process of expansion, just that you need plants involved for them to grow.

(light folk music) (soft thoughtful music) We're in Altadena, California, and we're standing on a site that had the entire home burned down.

So we did some soil sampling to figure out what contaminants were in the soil and start growing the fungi and gathering the materials to come back and do our remediation intervention.

And then we figure out which specific, you know, plants and fungi will be most effective for that site and its conditions and contaminants.

Then we will add those plants and fungi, so plant them, inoculate, and keep coming back to track how they're growing and keep testing.

And we do that until we get the contaminants below the health-based guidelines.

So the plan today for this site is to make and install the myco-wattles around the perimeter.

A typical wattle is just full of straw.

This is a really common method to prevent erosion and runoff of, like, toxic ash after fire.

And then what we're doing with myco-wattles is just adding fungi into the mix that have been already demonstrated to be able to deal with post-fire ash contamination.

Still the same goal of preventing any erosion, but also trying to break down some of the contaminants within that ash and hold onto and kind of filter any metals that might be passing through as well.

(Lively folk music) Ta-da!

Finished myco-wattle.

(laughs) (birds chirping) I grew up on the shores of Lake Erie.

Some of the tributaries to Lake Erie used to catch on fire from oil because there's so much tanker traffic through the lake.

So it is an incredibly polluted area that I also love so much, right?

I grew up as this, like, kid who loved to be playing outside, swimming in the lake, sailing on the lake, and also going on big walks.

When I was a teenager, on my walks and explorations, I would often see mushrooms popping up around, like, an old oil refinery.

I would see all kinds of plants coming back up, pushing up through the pavement, and growing.

And it really made me start to think that, you know, nature knows how to heal itself, and that if, you know, we leave it, you know, kind of let it be, that life can take over again and regenerate.

I do remember being quite young and asking, 'cause, you know, I'd hear, like, "Oh, so-and-so just got cancer, did you hear?"

You know?

And I was like, "Hey, doesn't it seem like there's a lot of this here?

Like, why does everyone have cancer?"

And it made me wonder if there wasn't something there.

I totally get, in this human way, that it's difficult to look at some of this stuff, the pollution and the pain and suffering that it causes of the land and people.

But I think we need to look at it so that we can deal with it.

(gentle contemplative music) So we're heading over to the sloped part of the site to put in this myco-wattle.

Putting it on the slope because these are designed to filter runoff and remediate it.

So slopes are where water will flow anytime it rains.

So that's why we're putting it over there.

Because this site is so toxic, our first priority is to contain the toxins by putting these myco-wattles around the perimeter of the site wherever there's any slope.

(shovel thudding) (Danielle grunts) So this soil is very compacted, (shovel crunching) so much that it's hard to get the shovel in.

It was hard to take samples.

(laughs) And the reason that matters is because, you know, it's gonna make it hard for plants to grow.

Plant roots will have a hard time reaching down through compacted soil, but the plants that we work with specifically have roots that can, you know, basically, like, puncture through compacted soil like this.

It's another major reason we wanna get these myco-wattles buried in the ground, because they'll start to heal the soil, and in doing that, they'll loosen it up and make it easier for plants to grow, too.

(light folk music) We're at a remediated site near Downtown LA, used to be a brownfield, and now it is remediated and clean.

These are California sunflowers that didn't grow (laughs) when the site was toxic, but now have bloomed now that it's clean.

So it's just such a sign of, like, the type of beauty that can happen once a site is cleaned up.

So this was an old auto shop, and it had lead and arsenic, and cadmium contaminants as well as petrochemicals.

And so we actually saw really good results.

In three months, we had pretty much 50% of all the petrochemicals were gone.

That's because of the decomposer fungi we put in.

And then after the year period, the petrochemicals were almost undetectable, and the metals were reduced below safe limits.

(gentle contemplative music) Coming back to this site and seeing all these beautiful flowers growing represents just what's possible for other contaminated sites around the country and definitely in California.

It's really emotional for me and really rewarding to get to come back over time and see how this space was transformed again, from a site that no one could use to something like this.

Just this beautiful space of possibility and community.

(waves lapping) (soft thoughtful music) I get so much hope and meaning and reward out of doing this work and then getting to witness healing happen.

It's really beautiful to me to see all that's possible in such a short time when we work with nature rather than against.

So, yeah, it's really something special when you see a flower bloom from a site (laughing) that was, like, just so bleak before.

And that is really rewarding for me and keeps me going.

(bright thoughtful music)