In 2017, Gavin Stonehouse, a graduate student in plant biology at Colorado State University, started cultivating hemp plants in a special soil mixture dosed with varying levels of selenium. A mineral that occurs naturally in most of the western United States, selenium is also a nasty environmental pollutant when produced in excess by industrial and agricultural activities.

Stonehouse wanted to find out if hemp could handle the selenium. If the plants thrived, it would be an important first step towards proving claims that industrial hemp naturally cleans soils contaminated with a multitude of toxic substances – a process known as "bioremediation" or "phytoremediation." The next step will be to discover just how much of the selenium the plants extract, and where the mineral ends up – in the plants' roots, stems, seeds or flowers.

Stonehouse and his advisor, CSU professor Elizabeth Pilon-Smits, plan to publish their results this summer. But the early indications are promising. The hemp was "super tolerant" of the selenium, says Stonehouse. Not a single plant died, and only a few, exposed to the highest doses, showed signs of stress.

The implications of the experiment go beyond just the potential for healthier soil. As humans have known for thousands of years, hemp is a plant that boasts abundant industrial, nutritive and medicinal properties. You can eat its seeds, treat pain and inflammation with its oils and make clothing, rope and paper from its fibers. And now, in the 21st century, we're discovering that it can perform like a kind of a toxic-substance vacuum cleaner too?

"If you can clean up the environment and still get a commercial product," says Stonehouse, "you are killing two birds with one stone."

The term "phytoremediation," was coined by the scientist Ilya Raskin, a member of a team that tested hemp's ability to accumulate heavy metals from soil in contaminated fields near Chernobyl in the 1990s. According to another team member, Vyacheslav Dushenkov, the experiment was a success. "For the specific contaminants that we tested, hemp demonstrated very good phytoremediation properties," says Dushenkov,

In 2001, a team of German researchers confirmed the Chernobyl results by showing that hemp was able to extract lead, cadmium and nickel from a plot of land contaminated with sewage sludge. In 2011, hundreds of farmers in Puglia, Italy, started testing the theory, planting hemp in a long-term effort to clean up fields disastrously polluted by a massive steel plant. (Conclusive data on how well the Italian bioremediation project is working doesn't appear to be available yet, but the farmers have been cleared to sell harvested hemp fiber for industrial use.)

Pilon-Smits, the CSU professor, has been studying phytoremediation for more than a decade. She had long been aware of the international research suggesting hemp was a prime candidate for environmental cleanup. But until very recently, her hands were tied. For nearly a century, commercial cultivation of hemp was forbidden in the United States, fallout from the widespread panic over marijuana that swept the Western world in the 1930s. (Hemp and marijuana are strains of the same species, cannabis sativa; the primary difference is that marijuana gets you high, and hemp does not.)

Even after Colorado legalized recreational marijuana in 2012 and passed a bill encouraging research into hemp's phytoremediative qualities in 2014. That same year, Congress added a provision to the farm bill that legalized the cultivation of hemp for research purposes, but Pilon-Smits still found it difficult to get academic funding for research. (Although numerous states have passed legislation encouraging industrial hemp cultivation and normalizing marijuana laws, both substances are still federally restricted. Even in forward-looking Colorado, suggests Pilon-Smits, a university that gave the go-ahead to research on hemp might run the risk of losing federal funding.)

But in the last couple of years, the political climate has changed drastically. In April, ultra-conservative Republican Mitch McConnell, the Senate Majority Leader, introduced the Hemp Farming Act of 2018 which would specifically remove hemp from the Controlled Substances Act. McConnell is currently maneuvering to get his stand-alone hemp bill incorporated into the 2018 Farm Bill.

In 2017, when Colorado Cultivars, a company that operates several industrial hemp farms, approached Pilon-Smits to ask if she was interested in analyzing hemp's potential for cleaning up soil, she jumped at the chance. She quickly brought on Stonehouse for the hands-on work, and started, as far as she knows, one of the first comprehensive research efforts in the United States aimed at establishing hemp's qualifications as an environmental savior.

If that sounds like a hippie dream, that's because it is. For decades activists fighting for the normalization of marijuana laws have touted the manifold beneficial uses of hemp as a kind of stalking horse for pot legalization. The somewhat fuzzy logic seemed to be that if laws against hemp were loosened, the case for marijuana's legalization would be strengthened. But in a sequence of events unimaginable a decade ago, the opposite happened: pressure to ease restrictions on marijuana ended up paving the way for hemp's redemption. The groundswell that emerged from the spread of medical marijuana led directly to what Doug Fine, author of 2014's Hemp Bound: Dispatches from the Front Lines of the Next Agricultural Revolution, calls the "hemp renaissance."

For Fine, hemp is nothing less than a savoir of humanity, a miracle plant that will revivify depleted soils, mitigate the threat of climate change, and re-establish harmonic balance between humans and the environment.

"It is the most important plant for the future of humanity,"

Says Fine, speaking to Rolling Stone from Hawaii, where he is working as a hemp-seed oil researcher for the University of Hawaii. For Fine, the vision of a hemp lifecycle in which the plant is used to remediate soil and then converted into environmentally friendly products is an example of "regenerative values" that are currently leaking out of the crunchy hippie communities and spreading "into the basics of our economy and society."

And at first glance, there are any number of reasons, according to Pilon-Smits and Stonehouse, why hemp has superstar phytoremediative potential. Hemp is a hardy plant that grows like, well, a weed, just about anywhere. It produces a relative abundance of bushy biomass in a short period of time, which means it is highly effective at extracting nutrients from the soil and converting them into potentially useful products. Its relatively deep and extensive root structure, unusual for an annual plant, allows it to probe widely through contaminated soil. It is also naturally resistant to insect predators, thus obviating the need for pesticides.

The full environmental picture, however, is not quite so balmy. As with most commercial crops, industrial cultivation of hemp depletes the soil of key fertilizing compounds such as nitrogen, phosphorous and potassium. Producing all that biomass requires significant inputs of water and runs the same risks of soil erosion as other industrial plants. A hemp-based economy, in other words, doesn't automatically usher in a green future.

There is also still a great deal to learn about what can be done with hemp plants that have been deployed to clean up especially dangerous contaminants. There is unlikely to be a market, any time soon, for edible hemp seeds or CBD oil from plants that have been used to extract cadmium or lead from Superfund sites. And at present, we simply don't yet have enough data to understand exactly how hemp stores the contaminants it extracts and what that might mean for possible health implications.

Still, it's possible to visualize some sweet spots where everything comes together. One of the reasons why Pilon-Smits and Stonehouse are excited about their selenium research is that even though excess selenium is an environmental pollutant, it is also, in small doses, a necessary nutrient for human life. Over a billion people in the world are selenium deficient, says Pilot-Smits. If industrial hemp removed selenium from the earth and concentrated it in edible hemp seeds, it would be possible to simultaneously clean up the environment and improve human nutrition.

"If hemp grows well," says Pilon-Smits, "the phytoremediation will pay for itself. There are many degraded or marginal soils that are taken out of production and polluted soils awaiting cleanup because there are not enough funds available to pay for it. Hemp can really be a solution."