By Ruth Thornton
A common practice by farmers to fertilize their fields may be spreading forever chemicals into new areas and into the food supply.
Biosolids are nutrient-rich organic materials derived from the treatment of sewage sludge from wastewater treatment plants that are applied as fertilizer.
They can be a cost-effective way for local governments to dispose of sewage sludge and for farmers who pay little or nothing to use it as fertilizer.
“Solids handling is a cost for municipalities,” said Christian Smith, the PFAS in Biosolids contact for the Department of Environment, Great Lakes and Energy, commonly referred to as EGLE.
“Whether that’s through land application, landfill or incineration, those are all typically done at a cost to the treatment plant,” he said.
Biosolids tend to be more cost-effective methods than other disposal methods for wastewater treatment discharge, said Sarah Campbell, the statewide coordinator for EGLE’s biosolids program.
To ensure that treated sewage sludge is safe to apply to fields, treatment plants remove pollutants including heavy metals such as arsenic, lead and mercury, she said.
But contamination by so-called “forever chemicals,” also known as PFAS, short for per- and polyfluoroalkyl substances, is a new kind of contamination that treatment plants aren’t well equipped to treat, according to Smith.
PFAS chemicals have been manufactured since the 1940s and are used in many consumer products, including food wrappings, clothing, carpeting and firefighting foam. Other important sources are industries such as metal plating facilities.
Most of these chemicals are not well studied. Some are associated with significant health problems, including cancer, thyroid disease, liver damage, decreased immune system response to vaccines and others, according to the Department of Health and Human Services.
Because of the potential for contamination, biosolids come with many restrictions on their use to ensure the safety of the food supply, Campbell said.
For example, crops grown on fields treated with biosolids are usually used only for animal feed or ethanol, she said. There are strict requirements for how and when they are applied, at what concentrations and what crops may be grown on them.
“While we allow food to be grown for humans, typically a lot of sources won’t buy it if it is known to be grown in biosolids,” Campbell said.
In fiscal year 2024, about a third of sewage sludge was applied to Michigan farms as biosolids. About a quarter was exported out-of-state, including to Wisconsin and Ontario.
Less than half was either landfilled or incinerated.
“Incineration actually is one of the more expensive ways,” Campbell said. “We’ve only got three incinerator stacks in Michigan, they’re all in Detroit. Because of air quality concerns, it’s not a very efficient process.”
Campbell said biosolids are often supplied free to farmers, though some municipalities may charge transportation costs.
The Environmental Protection Agency released a draft risk assessment in January to evaluate the risk for two of the most prevalent PFAS chemicals in sewage sludge. The public comment period is open through March 17, Smith said.
Smith said EPA’s leadership is important for states.
“Until this risk assessment came out, there was really no federal guidance,” he said. “And there is still technically no guidance on PFAS in sewage sludge.”
Abigail Hendershott is the executive director of the Michigan PFAS Action Response Team, which consists of state agencies, including EGLE, the Department of Transportation, Department of Agriculture and Rural Development.
Michigan is unique among states in establishing an interagency organization to target PFAS pollution, she said.
“Basically, in the country, we don’t have any other agency that I know of that has established this kind of a collaborative, interagency organization to specifically tackle PFAS,” Hendershott said.
“When we talk about the PFAS cycle, you’re not just talking about one pathway,” she said.
“You’re talking about the fact that PFAS can be released in a variety of ways,” she said.
“It can end up in our wastewater treatment plants, can end up in our landfills, in our air, in our rivers and groundwater,” she said.
Despite the lack of guidance from EPA on how to handle PFAS in sewage sludge, Michigan implemented an interim strategy to address biosolids in agriculture, Hendershott said.
Jared Driscoll is the water reclamation director for Midland. Biosolids produced by the city’s wastewater treatment plant were within the guidelines for safe application on farm fields, according to EGLE.
“I think most of our biosolids are land applied agriculturally,” he said.
“We pay a third-party contractor to collect, haul and inject the biosolids into the field, and the farmers do not pay us for the biosolids,” he said.
A 2022 analysis from the Agriculture and Rural Development Department estimated that application of biosolids saved farms in the state more than $10 million in fertilizer costs each year.
It also reduced municipalities’ sewage treatment waste disposal costs by nearly $8 million each year.
About 35,000 acres, less than 1 percent of Michigan’s farmed acreage, were treated with biosolids in 2022, according to the Agriculture and Rural Development Department.
While one farm in Livingston County was shut down because of PFAS contamination in biosolids, testing by EGLE hasn’t found other farms with PFAS levels above allowed amounts.
Tess Van Gorder, a conservation and regulatory specialist with the Michigan Farm Bureau, said the organization would like to see strong support for research on PFAS.
“So that when things happen, there is a safety net,” she said. “Farmers are unknowingly accepting these biosolids that have PFAS. This isn’t something that comes from the farm – it comes from off the farm.”
“We want biosolids to be safe,” she said. “We want good research on PFAS to make sure we understand the ways it moves through the system, and also funding for farmers in case they are impacted.”
But questions remain about the safety of biosolids.
A recent study in Nature’s Scientific Reports examined PFAS chemicals in 10 farms in Pennsylvania. It found that most fields treated with biosolids had higher concentrations of PFAS than fields without biosolids additions.
Still, the study’s lead author, Diana Oviedo Vargas with the Stroud Water Research Center in Pennsylvania, cautions against banning biosolids altogether.
She instead emphasized the need to monitor the applied biosolids for PFAS.
“Screening of the biosolids before they go out in the field is so important,” she said. “Banning across the board without really knowing that they were all problematic has a lot of implications too.”
“That’s not necessarily the most sustainable thing to do because now you have to deal with all of the biosolids,” she said. “Where are they going to go?”