Northern Michigan University researchers are exploring the feasibility of using hemp to remediate soil contaminated with PFAS, a group of manufactured chemicals that make a wide range of industry and consumer products non-stick, greaseproof and flame retardant. NMU Chemistry Professor Lesley Putman said the hope is that hemp will not only draw up PFAS from the ground, but ultimately be able to degrade them, unlike the typical and more costly remediation methods using granular activated charcoal or reverse osmosis.
Though the chemicals have been used since the 1940s, there is escalating concern because many break down slowly and can accumulate in people, animals and the environment over time, according to the EPA. Putman said PFAS tend to be lumped together into one group, even though not all are toxic and the molecules vary in size. She and three students in her lab first experimented with a small type that is not considered toxic, perfluorobutanoic acid (PFBA).
“We grew industrial hemp hydroponically and added PFBA to the water in which the plants were growing,” Putman said. “The hemp took it up into the leaves, stems and flowers, and it didn't affect the growth of the plant. We got the same result in a greenhouse, planting the seedlings in soil and applying water containing PFBA. Then we did the same experiments with the two main toxic chemicals: PFOS and PFOA. Because those are larger molecules that don't move as easily and aren't as water-soluble as small ones, they didn't go up into the leaves as readily and were sequestered in the roots. But nevertheless, if hemp can hold them up, that's a good starting point.”
Putman did not have to search far to find practical applications for the research. Wastewater from the sewage treatment plant at the former KI Sawyer Air Force Base had tested positive for PFOS, the same substance she said was reported at a base in Maine, where a group grew hemp to remediate contamination attributed to longtime use of firefighting foam. Putman attended a day-long information session at Sawyer, and also picked up two buckets of sludge from there to bring back to her lab.
“We mixed the sludge with soil and grew hemp in it,” she said. “We found PFOS as the primary contaminant in the hemp roots. Meanwhile, the Marquette Solid Waste Facility got a consent order from the state that indicated unacceptable levels of PFOS and PFOA in the leachate and requested a plan for fixing it within five years. They're aware we are working on this research, but it's too early to say whether hemp would be a viable option for Marquette. Granulated activated charcoal could filter out the chemicals and keep them out of the water stream. But then what do you do with the activated charcoal afterward? Putting it back in the landfill wouldn't make sense.”
Even if hemp proves equally or more effective than activated charcoal in preventing PFAS from permeating the water table, “You're still left with plants that contain toxins,” Putman said. NMU contracts with a company that safely removes and stores all toxic waste generated by her research, but a large-scale contaminated site solution is dependent on finding a way to degrade PFAS once they're taken up by the hemp plants.
Recognizing that enzymes produced by mushrooms can effectively break down different pollutants in soil—a process called mycoremediation—Putman is in conversations with Myconaut, a Marquette business co-founded by NMU alumnus Joe Lane that explores the varied potential of fungi. “Maybe we could inoculate some of the hemp roots with a fungus and see if that helps to degrade the PFAS,” she said.
Putman is also aware of a researcher in Belgium working with hemp to counter PFOS contamination from a 3M plant in Antwerp. She said there have been isolated studies using hemp for toxic PFOS; most previous research using hemp has explored its uptake of metals. Her next plan is to do field trials, growing hemp in above-ground planters, watering the hemp with a leachate containing PFOS and measuring how much is sequestered by the roots.
“I feel extremely fortunate that, as an undergrad, I get to do this kind of research with practical implications that could improve on what's being done now,” said NMU student Asbel Wells. “Not every student gets an opportunity to work with something this relevant. I'm really excited and passionate about it, and hope I can make a difference.”
“I've really enjoyed using hemp in a way that extends beyond its fibrous use and medicinal values,” said student Dominic Dotson. “This would be a way to further increase the potential uses of this plant, and we could get hands-on experience locally where we might contribute as well, aside from just working in the lab.”
“I like the idea of working with PFAS, especially at this time because it's a compound that people are really starting to pay more attention to in the environment,” added student Kevin Schick. “It's cool to be on the forefront of this type of research and see how we can get it out of the environment.”
The MSU Extension farm in Chatham put Putman in touch with a supplier of hemp seeds known to grow in this area. There are hundreds of varieties, but by definition, all have less than 0.3% THC. If hemp becomes more established for phytoremediation, other researchers will breed it to find a variety that optimizes that function, Putman said, much like a Wisconsin group is doing through phytoremediation studies with poplar in that state and the Upper Peninsula.
It was a chance encounter on a week-long trip aboard the 1,000-foot Great Lakes freighter Paul Tregurtha that connected Putman with area officials who could advance her work. During a conversation about her research with fellow passenger Margaret Brumm, an adjunct assistant professor in NMU's College of Business and a former member of the City of Marquette's wastewater treatment committee, Putman shared her interest in finding practical applications for testing hemp's capabilities. Brumm connected her with an individual at Sawyer who provided the PFAS contaminated sludge samples. For further work planned, Brumm has purchased soil cubes and above-ground planters that are ideal for ensuring contaminants aren't released during the field studies.
Hemp's many uses include health products, foods, fabric and rope. Putman and her students are exploring its potential value as a phytoremediation option. Their research is particularly relevant, given mounting concerns that PFAS contamination is ubiquitous in the environment and can pose health risks with significant exposure over time.