NMU researches hemp for PFAS remediation

Northern Michigan University (NMU) 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.

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