Are Biosolids a ‘Forever Chemical’ Risk?

Friday, July 24, 2026

U of G researchers are investigating PFAS concentrations in land-applied biosolids

By Emily McKinlay

’Forever chemicals’ — officially called per- and polyfluoroalkyl substances (PFAS) — are a common component in many household products, but their chemical makeup and resistance to decomposition have led to increasing concentrations of PFAS in the environment. In some regions, biosolids have been under scrutiny for their potential relationship to PFAS concentrations in soils.

Dr. Ryan Prosser, associate professor in the School of Environmental Sciences at the University of Guelph, wants to know if applying biosolids on crop land increases the concentrations of PFAS in the harvested crop.

“PFAS are a broad group of chemicals that contain a lot of strong fluorine-carbon bonds. They have a lot of applications and are used in a lot of products because of their unique properties,” says Prosser.

PFAS are used as surfactants, lubricants, and repellents and are found in many products, including cosmetics, food packaging, textiles, and cleaning products.

“PFAS can be a concern because they are persistent and don’t break down readily in the environment,” says Prosser.

“We have found them in blood and in tissues now. They are not readily excreted by the body and don’t tend to break down. There is also a potential for PFAS to be taken up by livestock. The biggest concern is that they don’t break down like a lot of other chemicals we would use in agriculture or society in general.”

The persistence of PFAS in the environment is cause for concern for agriculture and food production in Ontario. While biosolids have provided a valuable and sustainable source of nutrients and organic matter for farmers, their origin in human waste makes them a potential source of PFAS.

Biosolids & PFAS

Biosolids are a by-product of municipal wastewater treatment. They have become a common nutrient and organic matter source for farmers across Ontario.

“A large proportion of biosolids in Ontario is land applied. They go back onto agricultural land and provide important crop nutrients such as micronutrients, nitrogen, phosphorus, and organic matter,” says Prosser.

“It’s a win-win solution. It is often free for farmers if it’s part of a program with the municipalities, and it benefits the municipality in managing wastewater and sewage. It’s a sustainable approach. Traditionally, nutrients tend to move from rural to urban areas, and this is one way to close the loop without adding synthetic nutrients.”

Prosser notes that the programs have been so successful that there are often more producers on the list to receive biosolids than there is availability. Despite the success, there is a contamination concern with biosolids.

“Because biosolids are coming from wastewater treatment facilities, there is concern they could be contaminated with pharmaceuticals, cosmetic products, microplastics, and PFAS.

“PFAS recently have received a lot of attention in relation to biosolids, and people are wondering if we are increasing concentrations in soil and crops because of biosolid application.”

An incident in Maine sparked interest in investigating PFAS concentrations in biosolids.

“This interest really kicked off a few years ago when the state of Maine banned the application of biosolids because of PFAS,” says Prosser.

“There were some biosolids with a high level of PFAS that were applied on farms and then contaminated soil and livestock. It was a worst-case scenario that set off a chain reaction. A number of other states started to evaluate the use of biosolids.”

This motivated Prosser to investigate Ontario’s practice of land-applying biosolids.

The study

Prosser’s study is a collaborative effort between the University of Guelph, the University of Toronto, OMAFA, and various municipalities and industry members throughout Ontario.

The three-year study is investigating PFAS concentrations at multiple stages in biosolid application. The first stage is to sample the biosolids themselves for PFAS, followed by comparing the concentrations in fields under the same management that have and have not received biosolids.

“We are sampling biosolids from municipalities across Ontario to measure PFAS and are working with farmers who are part of land application programs. We have farmers in the study who have fields that have received biosolids as well as fields that have not received biosolids historically, and we are looking to see if there are differences in PFAS levels.

“Biosolids are not the only source of PFAS. They can come from rainwater or aerial deposition and can be found in some pesticide formulations. We want to see if biosolid application in Ontario is making a considerable difference in PFAS levels in agricultural fields.”

Beyond testing for PFAS concentrations in the soil, Prosser’s team will look at PFAS in earthworms.

“They are the ultimate passive sampler as they cruise through and consume the soil.”

He adds, “The final part of the study is sampling the crop to see if there are differences in PFAS levels in the crops from land that has received biosolids. We are specifically looking at the commodity portion that would go into livestock feed or human food. This all comes back to the question: ‘Is biosolid application having a measurable impact on the PFAS in agricultural fields, and by extension, the crops that are grown in them?’”

The project is currently in the second year of three, and Prosser has shared results from the completed portions of the study.

The results

PFAS were detected in the biosolid samples collected for the study, but Prosser says that result is not surprising nor cause for concern on its own.

“The level in biosolids is relatively low, and we are not in a situation like the one in the state of Maine. PFAS are present — because they are everywhere — but at relatively low levels below what would pose a risk to ag fields.”

Source control of wastewater in Ontario plays a major role in reducing PFAS concentrations in the province’s biosolids.

“Municipalities in Ontario do a pretty good job at source control. They are typically very careful about what kind of industries are discharging wastewater to the municipal wastewater plant. Some industries can produce wastewater that is high in contaminants, PFAS, and metals that need to be treated in a whole separate way.”

He notes that during the PFAS issue in Maine, source control was not performed to the same degree as in Ontario.

While PFAS were present in the biosolids, the researchers found no significant differences in soil concentrations between fields that received biosolids and those that did not. The team also did not observe significant differences in PFAS concentrations in earthworms from those fields. The team is now analysing samples from crops grown in the fields and expects to share the results in the next year or two.

“The good news is that biosolids don’t seem to be a big contributor to PFAS in soils. The bad news is that we found them in all the things we tested, which is not surprising. We know they are widely found because they are so widely used,” says Prosser.

Based on the preliminary results of the study, Prosser continues to believe that biosolids are a sustainable source of nutrients for crops in Ontario. The concentrations found are at a level that does not approach those that prompted the ban on land-applying biosolids in the crisis in Maine.

“Banning biosolid applications because of PFAS is a bit like cutting off your nose to spite your face. The issue is upstream and regulatory.”

At the concentrations observed in the study, Prosser suggests that PFAS exposure from agricultural sources is likely a lower risk than the exposure from household products.

“Banning biosolids is not going to solve the PFAS problem. They are in non-stick surfaces, cosmetics, and fabric treatments, and those are probably a much greater issue for human exposure than the small amount that goes on ag fields,” says Prosser.

Although the biosolids tested in the study did not significantly contribute to the PFAS in agricultural fields, Prosser believes it is still a problem worth discussing and monitoring.

“I do encourage producers to have an open dialogue with the municipality they are receiving biosolids from and with the company doing applications. Municipalities are starting to do some measurements and screening of biosolids, so you can ask them if they have been measuring PFAS.

“In Ontario, we are in pretty good shape, but we should continue to monitor PFAS to make sure they don’t considerably increase. I think the benefits of land application of biosolids far outweigh the costs. There are benefits to municipalities and farmers. Nutrient cycling is really important, and I would hate to see programs stopped because of contaminants we’ve failed to regulate.”

As the team continues to analyse the data from this study, Prosser is considering future investigations into PFAS in agricultural settings and ways to mitigate risks to the food chain.

“We would like to do more work in terms of what PFAS are present in crops to understand which are most likely to be taken up into the plants.

“The different PFAS molecules behave differently, so we would like to look at which ones we are seeing in soil and which of those are most likely to be taken up by the crop. Maybe some are not readily taken up by crops at all, or maybe there are other PFAS we need to be focusing our attention on. That’s where our work is going.” BF