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Toxic waste, by definition, is harmful to living things, but there are actually a bunch of plants, animals, fungi, and microbes that can help us clean it up!

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[♪ INTRO].

Humans have done a lot to pollute the world we live in, contaminating soils and water with everything from oil to radioactive waste. Luckily, some parts of nature have evolved to survive this pollution, and might even be able to help us clean up these contaminants.

Using living organisms to get rid of toxic waste is called bioremediation. It’s safe and cost-efficient, and we’re discovering new ways to do it all the time. Bacteria are often the go-to bioremediators, but certain plants and animals can pitch in too.

Here are 7 organisms with the potential to make our world a cleaner place. Fungi are so useful for bioremediation that there’s a special word just for them: mycoremediation. Fungi grow quickly and are great decomposers, using networks of threadlike structures called mycelia to burrow into organic material like decomposing trees and inorganic material like rocks.

Mycelia are actually the main body of a fungus; mushrooms are just a temporary reproductive structure. As they dig through the soil, mycelia ooze a variety of chemicals known as extracellular metabolites. These are enzymes and other compounds that break down molecules, including potentially toxic ones, into pieces that fungus can digest and absorb.

Researchers who study fungi have found over 120 different enzymes being produced by different species. And in the 1990s, a mycologist named Paul Stamets helped develop a strain of oyster mushroom with enzymes called peroxidases, which can break down hydrocarbon molecules in oil-contaminated soil. This is a big deal because oil contaminants can take a really long time to decompose, and have all sorts of toxic effects on the ecosystem in the meantime.

Oyster mushrooms and other fungi have been deployed as an experiment to clean up the aftermath of oil extraction in the Amazon rainforest, and in an oil-contaminated creek in New York City. That’s something to think about the next time you’re picking mushrooms off your pizza! It turns out that cheerful sunflower plants can be great at sucking up radioactive contaminants.

After a nuclear disaster, radioactive isotopes typically stick around in soil and water, continuing to emit harmful ionizing radiation for decades. But some of these radioactive molecules are physically and chemically similar to some nutrients that plants need, like potassium and calcium. So as some plants grow, their roots can absorb the radioactive isotopes right alongside these nutrients.

Sunflowers work especially well for this, because they can grow pretty fast and can thrive in a lot of different climates. What’s more, they accumulate these isotopes in their shoots and stems, making it fairly easy to dispose of contaminated plant matter. After the meltdown at Chernobyl in 1986, a company working on the cleanup built rafts of sunflowers with roots dangling into contaminated ponds.

The sunflower plants sucked up cesium-137 and strontium-90. And removing those contaminants with this method cost only two to six dollars for every thousand gallons of water, which is pretty cheap! The method was less effective for soil, because some radioactive isotopes can nestle tightly into tiny cavities in clay, where they’re harder to extract.

But sunflowers work well enough that they’ve also been used to try and clean up groundwater at a uranium-processing plant in Ohio, contaminated springs at the Oak Ridge National Laboratory in Tennessee, and even around Fukushima. Bivalves are mollusks with two-piece hinged shells. This is the group that includes clams, oysters, and mussels.

They’re constantly filtering the water around them, because they’re after tiny, free-floating organisms like plankton. But in the process, they also suck up chemicals like weed killers, pharmaceuticals, and flame retardants, as well as removing gunky sediment and algae that can mess up ecosystems. This can be rough on the bivalves’ immune system, but in many cases they survive.

This has led to a lot of interest in restoring natural oyster populations in places like Chesapeake Bay. And some scientists are even experimenting with bivalves in other places in need of clean-up. For a 2014 study, researchers looked at two bivalves: a mussel species from California and an invasive variety of Asian clam.

They put these species into tanks and flowed wastewater spiked with 7 chemical contaminants through them. After 72 hours, the bivalves had sucked up and processed 80 percent of one contaminant, triclocarban, and smaller amounts of the others. Triclocarban is an antibacterial chemical that’s often used in hand soaps.

If it’s in the water supply, it’ll kill some bacteria. But any microbes in the water that happen to mutate and survive will reproduce and be more resistant to triclocarban, or possibly other antibacterial compounds they come across. Which isn’t good for us if they cause disease.

Plus, triclocarban can also have effects on hormones in living things. The same group of scientists then tested their bivalves in a polluted lake in San Francisco known to have high concentrations of E. coli bacteria. And some strains of E. coli can make people sick.

They fed water from the lake through tanks of bivalves and took some samples of the water going in and the water coming out. And turns out the mussels efficiently filtered the bacteria out of the lake water, digesting it with no apparent bad effects. Lead-contaminated water has been in the news a lot in recent years, partially because of the ongoing crisis in Flint, Michigan.

Lead builds up in our teeth and bones, spreading to other parts of our body from there and interfering with the brain, liver, and kidneys. Which… becomes a big problem. We’ve been developing filtration devices that remove lead from water, but a recent study shows that a species of moss may be able to help.

Japanese researchers found a possible lead decontamination option in bonfire moss, known to grow well in sites contaminated with heavy metals, which are just metallic elements that tend to be pretty dense and toxic. The scientists exposed the moss to solutions with varying concentrations of 15 different metals. About a day later, analysis with a mass-spectrometer showed that the cells of the moss samples that were exposed to lead had absorbed enough to make it around 74% of their dry weight.

Most of that lead was in the cell walls of the moss, and the scientists couldn’t determine the exact mechanism. But a different analysis showed that these cell walls contained an unusually large amount of a compound called polygalacturonic acid. So they think it might be involved in binding lead atoms somehow.

Applying this to real-world cleanup is still in the future, but the researchers definitely think it has promise. Especially because the lead uptake worked across different conditions. Who knows, maybe someday lush carpets of moss will be a part of our water treatment systems.

There’s a humble-looking plant species with white flowers called alpine pennycress. It’s a member of the cabbage family, and it has an unexpected superpower. When it grows in soil contaminated with heavy metals, it concentrates a bunch of them in its leaves.

Like, more than 100 times the heavy metal concentrations that a typical plant can handle. That’s why it’s considered a hyperaccumulator. There are actually hundreds of hyperaccumulator species in the world, but alpine pennycress is pretty unique.

It’s one of only three species known to take in cadmium, and the only one that can do both cadmium and zinc. Like with lead, chronic exposure to these heavy metals can have a variety of health impacts on humans. Cadmium can cause severe liver and kidney problems, and too much zinc can cause vomiting, fatigue, or mess with your immune system.

Part of the secret behind this plant’s ability lies in specialized transport proteins, although other molecular pieces are probably involved. In most plants, transport proteins regulate the accumulation of heavy metals in cells, letting the plant take in low levels but rejecting them once the concentration reaches a certain point. But alpine pennycress seems to lack this kind of regulation; it just keeps sucking up more heavy metals with seemingly no adverse effects.

Unfortunately, pennycress plants are too small to have a big remediation impact on their own, but researchers have been looking into how to harness the molecular mechanisms at work. In 2011, for example, Chinese researchers managed to express the gene for a key alpine pennycress enzyme in tobacco, which significantly increased its ability to accumulate cadmium. Now, that tobacco plant with an alpine pennycress gene wasn’t the first tobacco plant engineered for bioremediation.

In 1999, researchers in the UK inserted a gene from a bacteria species into tobacco. The gene coded for a protein called PETN reductase, which is capable of digesting two nitrogen-based compounds. One’s called pentaerythritol tetranitrate, or PETN, and the other is glycerol trinitrate, or GTN.

Both of these chemicals are powerful explosives, and sometimes military and industrial activity leaves trace amounts of them behind in soil. Which is not good. When the scientists tested out their creation, they found that the plain tobacco plants they used as controls could barely grow at all in soils containing even just a little bit of GTN.

The engineered plants, on the other hand, not only sprouted and grew at a normal rate, they also absorbed and broke down the explosive compounds. Since then, scientists have turned their attention to another nitrogen-based explosive that you’ve probably heard of: 2,4,6-trinitrotoluene, or TNT. For a 2007 study, tobacco plants engineered with both the PETN reductase gene and a second bacterial gene for breaking down nitrogen compounds were grown in soil spiked with TNT.

Not only did the plants lower the concentration of TNT in the polluted soil, but in doing so, they also seemed to help out nearby microbes. Both the biomass and metabolic activity of bacteria growing around the roots of tobacco plants increased. And since microbes are essential for soil health, that’s good news too.

Wax moth caterpillars are probably most familiar to two kinds of people: anglers and beekeepers. They’re bred and sold as premium fishing bait. And in the wild, they eat beeswax and are a major beekeeping pest.

But a scientist and amateur beekeeper discovered by accident that they’ll also chow down on something else: plastic. She removed some wax moth caterpillars from one of her hives and put them into a plastic bag. And later, she was surprised to find that they’d eaten their way out.

Then she did a follow-up study in a lab, which was published in 2017. And experiments showed that in just half a day, a hundred worms could eat almost a tenth of a gram of polyethylene. Scientists also smashed up caterpillars and spread the goo on plastic surfaces.

And that goo ate holes in polyethylene, too. This test confirmed that an enzyme in the caterpillar was truly breaking down the plastic, they weren’t just chewing it up into smaller bits. This is a big deal because polyethylene is used in a lot of packaging.

Some estimates say about 40% of the plastic products today are made of this stuff, and it doesn’t easily break down on its own. We don’t know yet exactly what enzymes are involved in the caterpillars’ plastic-eating prowess, but presumably it’s the same ones they use for digesting wax. So, the next step will be identifying those enzymes and figuring out how to put them to work breaking down plastic waste.

Some have raised concerns that breeding lots of these wax-eating caterpillars could put bees at further risk, but maybe their plastic-destroying genes could be stuck into bacteria or something else. So if science looks hard enough, there’s probably a plant, animal, mushroom, or microbe out there that can help us deal with pretty much any kind of toxic waste. Adaptations can be pretty incredible.

Thanks for watching this episode of SciShow! If you want to learn more about pollution and how it’s being cleaned up, check out our video about some of the most toxic areas in the United States, called superfund sites. [♪ OUTRO].