Keith Hunter was looking forward to buying his mother’s 100-acre hay farm in Unity, so she could retire comfortably and he could run it with his sons and daughter. But bad news squelched his plans in early 2022.
A customer reported that the hay purchased from Hunter Farm had tested positive for forever chemicals. Hunter and his mother, Sue Hunter, immediately collected dozens of soil and water samples that showed the farm was highly contaminated by the chemicals, including in the groundwater used for irrigation and the drinking water.
Known as per- and polyfluoroalkyl substances, or PFAS, forever chemicals do not easily break down. They make plants uneatable and milk undrinkable, and they are linked to some cancers in humans. Hunter Farm could no longer sell its hay, and Keith Hunter’s dairy herd on his own farm nearby was contaminated from eating the Hunter Farm grass. But he and his mother weren’t ready to give up.
“We want to farm the land,” Keith Hunter said. “We want to find a solution.”
Two key developments may hasten a fix for his farm and potentially dozens of others in Maine contaminated with PFAS. In October, a second Maine factory began commercial production of biochar, a wood waste product that holds promise for absorbing and sequestering PFAS in soil, before it gets into crops. And the state’s $60 million PFAS Fund, established in 2022, is offering grants to study PFAS uptake in plants and how to minimize it. Both could potentially revitalize tainted farms in Maine, most of which are still operating but not at their previous capacity.
Three research projects are underway at Hunter Farm. One by the University of Maine and a second by a company called Northern Tilth are focused on discovering to what degree biochar is capturing PFAS by mixing it into the soil. Early results are expected at the beginning of next year. The third project, also by University of Maine researchers, is examining which plants take up more or less PFAS naturally. For example, tomatoes take up little, and lettuce and other leafy greens and animal feed grasses take up the most.
Results of the first two research projects are likely to vary by how much biochar was mixed into soil for a particular experiment, what type of soil was present, the amount of PFAS present in the soil — as it can vary across farmland — and what types of crops were tested.
The scientists hope to answer questions about which plants might be substituted in PFAS-tainted areas in the future, how much PFAS biochar can capture, how long biochar holds onto PFAS, how much biochar is needed to help clean a field, how often it must be applied, and whether it keeps enough PFAS from getting into crops so that they are safe for humans and animals to eat.
Biochar, a very porous, charcoal-like substance, is made from organic biomass such as low-value forest and agricultural waste heated at high temperatures. It does not destroy PFAS but instead encapsulates it for a long time. Scientists do not know exactly how long, but they believe biochar can stay in the soil for decades and can also help reduce carbon dioxide emissions.
Maine as a leader in PFAS research
Maine is ahead of other states in conducting research on PFAS and biochar, largely because of its big forestry industry, said Ling Li, assistant professor of sustainable bioenergy systems at the University of Maine’s School of Forest Resources.
Li and her colleagues began conducting tests last year on Hunter Farm to study the effect of biochar on PFAS uptake in crops. One of the reasons the research interests her is because biochar provides another market for Maine’s forestry products.
Local biochar was hard to come by when she began her experiments. She had to get it from out of state. For the next round of experiments she plans to source it from Standard Biocarbon, which started commercial production of biochar in October at its Enfield factory.
“That’s a major force of why I want to do the biochar studies, for Maine’s abundant biomass to find a home, to get new products, materials and applications,” Li said.
UMaine has received $500,000 from American Farmland Trust, Maine Farmland Trust and the Maine Organic Farmers and Gardeners Association to support PFAS projects for up to two years. So far it has conducted tests in an open field and in a greenhouse, where weather and growing conditions could be better controlled. It is looking for four types of PFAS chemicals in the greenhouse studies and more than 10 types in the open fields.
The researchers added biochar in different concentrations to soil to see the effect in reducing the uptake of several different types of PFAS by plants. Those include two of the most well-studied PFAS, perfluorooctanoic acid or PFOA, and perfluorooctane sulfonic acid or PFOS. The UMaine experiment is measuring uptake in tomatoes, which are known to not take up many PFAS chemicals, and lettuce, which does, to see the effect of biochar in the soil on those plants.
Li said one challenge is that even when the data are analyzed, there are no published federal safe standards for the amount of PFAS in food as there are in water. The U.S. Environmental Protection Agency in April lowered the safe water standard for PFAS to 4 parts per trillion, down from 20 parts per trillion, starting in 2027.
“We need relevant regulations or guidelines on the limits of PFAS levels in food to guide the PFAS remediation research on crops,” she said.
First-year study results are due out early next year. Li is optimistic about how biochar will perform, and is applying to Maine’s PFAS Fund for money to start another round of experiments.
“Adding biochar can reduce the PFAS uptake by crops to different degrees,” she said. “The level of decrease will vary from species of PFAS, soil and the plants.”
She expects biochar to work better in the soil than compost and ash because it has a large surface area and is porous, so it can absorb more PFAS than other amendment materials.
Comparing soil additives
Another research group on Hunter Farm is testing various amounts of biochar and high-carbon ash in the soil. The ash is a byproduct of burning coal that is less expensive than biochar, but it may not be as absorbent. Those tests are being run by Northern Tilth, a Belfast-based company that conducts tests and measures PFAS levels for customers.
The experiments are focused on animal feed grass, which takes up one compound, PFOS, more than most other crops, said Andrew Carpenter, a soil scientist and owner of Northern Tilth. The tests also are larger scale with more biochar and high-carbon ash added to the soil than the University of Maine experiments.
“One of the biggest pathways of concern with contaminated fields is the transfer of PFOS from soil to grass to cow to either milk or beef,” Carpenter said. “The absorbants do not destroy or transform PFOS. They muckle onto it, essentially.”
One big question remaining about biochar is that scientists do not know how long it will hold onto PFAS.
“It’s a relatively long life, but we’re not sure how long,” Carpenter said. “Even if it is effective for 10 years or decades, it would be really helpful. But if it only works for a couple years, it would be very expensive to keep redoing.”
Northern Tilth is collaborating with Purdue University, which is based in Indiana. The trial on Hunter Farm is for two-and-a-half years, with the first year completed. Like Li at UMaine, he is applying to the Maine PFAS Fund to expand his experiments to a couple of other farms to study how long the PFAS absorption will last.
“In theory, pound for pound, biochar should be more effective than high-carbon ash,” he said. “But biochar is more expensive. High-carbon ash is like a poor-man’s biochar.”
Despite early promise, developing the agriculture cleanup market for biochar isn’t a slam dunk, Carpenter said.
“It hasn’t been used that widely, and it is a relatively expensive material,” he said.
‘A slow detoxification process’
Another recent study found that PFOS levels in livestock feed grass could vary dramatically from field to field on a farm. Researchers at the Maine Center for Disease Control and Prevention found that grass absorbed more PFOS if other types of PFAS, known as precursors, were present at high levels in the soil.
The researchers studied soil over three years on several farms throughout Maine that had different histories of spreading contaminated biosolids on the fields. They found that PFAS contamination could vary greatly in different fields on the same farm, a finding that could help farm managers better plan their crops. The study was published in the Oct. 8 issue of the Journal of Agricultural and Food Chemistry.
Tom Simones, assistant state toxicologist at the Maine CDC, said the findings are an important contribution to helping farmers manage affected farms.
“These new data fill a major gap and will improve our ability to more confidently predict the movement of PFOS from contaminated soil into forage crops fed to livestock and the resulting levels of PFOS in foods such as dairy milk or beef,” he said in a prepared statement when the research results were announced.
Farmer Keith Hunter has already figured out he must do a balancing act when feeding the 16 cows on his own dairy, Little Darling’s Dairy in Unity. He said PFOS, which can end up in a cow’s milk, works its way out of the animal’s body in about a year. Carefully monitoring feed for levels of PFAS continues to be an important part of keeping the cows clean. He and his mother consulted old maps and found the farm crops had been farmed in strips, so they had each strip tested individually.
“We’re pulling feed off from the lowest ones we have,” Keith Hunter said of the PFAS test results in soil. “It was basically a slow detoxification process for the cows that took over a year before we could sell milk again.”
Maine farmers can sell milk at the PFOS level of 210 parts per trillion set by the state. Since contamination levels vary on the various strips of fields at Hunter Farm, Keith Hunter has to check which strips the bales grew on carefully to ensure his cows don’t get too much PFOS cumulatively, across the bales.
“I have to line my bales up and say, ‘These came off this field, and these came off that one, so I can feed two of these bales and one of these, so it all evens out,’” he said.
His mother, Sue, combined optimism and skepticism as she talked about the possible benefits of biochar to help keep PFAS out of feed. She still remembers clearly when the state offered free fertilizer several decades ago. Because farmers struggle, when somebody offers free fertilizer, they’re going to take it, she said. Now, Hunter Farm and dozens of others across the state are contaminated with that free fertilizer, which turned out to be sludge containing PFAS.
“We took them at faith value, and, you know, now we have this,” she said.
But this time around, the Hunters are taking precautions. They are testing anything that goes onto their fields, which are certified organic.
“Our goal is to remediate the fields or find crops we can grow that do not pull up the PFAS,” Sue Hunter said. “There’s a lot of education that needs to go on to make people understand that it wasn’t the farmers that caused the problem.”
Lori Valigra is an investigative environment reporter for the BDN’s Maine Focus team. She may be reached at [email protected]. Support for this reporting is provided by the Unity Foundation, a fund at the Maine Community Foundation, and donations by BDN readers.
