In 1980, a federal law identified the most hazardous sites around the United States, those that contained toxic contaminants in urgent need of cleanup. These “Superfund sites,” named for the initial funding allotted to the cleanups, are chiefly old industrial sites contaminated with pollutants from substances such as metals, oils, hydrocarbons, and explosives, and which are dangerous to human health. On top of the 1,327 Superfund sites, there are more than 400,000 Brownfields sites across the country that are not under federal purview but are also perilously contaminated.

The cleanup process for this contaminated land is energy-inefficient and expensive—it often relies on hauling the toxic soil away or mechanically pumping it out of the ground to treat it. Now, a pilot program is testing out a greener and cheaper solution by planting trees to soak up the contaminants, and inoculating those trees with probiotics that make them resilient against the toxins. It’s a twist on an old technology known as phytoremediation, and with the promise that the new innovation will keep the trees healthy, an environmental nonprofit and a startup are collaborating to plant these contaminant-cleaning trees in municipalities nationwide, and get more cities on board with embracing the largely natural solution to a man-made problem.

The U.S. has a “legacy of contamination,” says Kyle Kornack, manager of social innovation and enterprise at the Arbor Day Foundation, a nonprofit that has planted 400 million trees since the 1970s in order to tackle “pervasive global issues” like poverty and climate change. Areas across the country are contaminated for a variety of reasons; most are former industrial facilities, gas stations, military bases, and dry cleaners. The contaminants, which have been found to cause cancer, birth defects, and cognitive problems, are released into the air and can be inhaled, but the majority are leaked into groundwater—the source of drinking water for 51% of the general U.S. population and 99% of the country’s rural population.

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