PFAS in pesticides: What farmers should know

“Are the PFAS in pesticides contaminating our land and water? Unfortunately, there really isn’t enough research yet to give us a firm answer,” said Faith Cullens-Nobis, an Extension educator with Michigan State University.

Despite the lack of a firm answer, Cullens-Nobis thinks farmers need more information about a class of PFAS (per- and polyfluoroalkyl substances) that are in the pesticides they’re spraying.

PFAS comprises thousands of manmade chemicals that have been used for decades in many consumer and industrial products. They are widely used because they provide water, oil, heat and stain resistance along with non-stick performance.

In pesticide applications, PFAS are used to improve product performance such as lengthening the timespan of the pesticides’ killing properties. PFAS can help pesticides penetrate the leaf surface to reach where they are active in the plant.

According to Sara Qian, a postdoc at MSU’s Center for PFAS Research, there is no single accepted definition of PFAS. It’s a vast umbrella; by some estimates there are over 14,000 different kinds.

Chemically speaking, all PFAS have one thing in common, whether they’re used in non-stick frying pans or pesticides. They all have carbon and fluorine (C-F) bonds, one of the strongest bonds in organic chemistry. These bonds are what give PFAS extremely high environmental persistence, which is why they’re called “forever chemicals.”

Widespread industrial use of PFAS started in the 1940s and ‘50s. Major contamination sources include military bases, airports, landfills and industrial sites.

PFAS have inadvertently been brought onto farms from contaminated sources, such as contaminated biosolids or paper pulp spread for fertilizer. Irrigation water from a contaminated water source – municipal or a private well – can also be a source. Once PFAS are in the water and soil of a farm, the chemicals can be taken up by crops and eventually people.

PFAS can also enter the farming system by spraying pesticides which contain them as an ingredient.

Short-Chain vs. Long-Chain PFAS

One of the simplest ways to classify PFAS is by long-chain and short-chain. Long-chain PFAS have more carbon atoms in their structure; short-chain PFAS have fewer carbon atoms.

For example, PFOS (a long-chain PFAS) has eight carbon atoms, whereas PFBS (a short-chain PFAS) has fewer carbon atoms.

Long-chain legacy PFAS like PFOA and PFOS were largely phased out in the early- to mid-2000s due to escalating concern about their negative impacts to human health including an increased risk of liver and thyroid disease and kidney and testicular cancer.

But long-chain PFAS were replaced with short-chained ones.

Qian said long-chain PFAS tend to bioaccumulate in humans and wildlife and are more toxic compared to the short-chain PFAS which are generally eliminated from the body more quickly.

“However, that does not necessarily mean that they’re more safe. We just don’t have that much research on the short-chain PFAS yet compared to the two legacy long-chain PFAS,” she said.

Researchers are actively studying the health impacts of short-chain PFAS.

PFAS in Pesticides

According to Cullens-Nobis, data from the last decade show a clear upward trend in pesticides containing short-chain PFAS.

The pesticides themselves contain short-chain PFAS, but inert ingredients such as solvents, carriers, emulsifiers, dyes, surfactants and defoaming agents might also contain them. Manufacturers, however, aren’t required to disclose inert ingredients to states. Cullens-Nobis cited research that showed that HDPE plastic pesticide containers have leaked PFAS into the products.

When pesticides containing PFAS degrade, they form trifluoroacetic acid (TFA), an ultra-short-chain PFAS and now the most abundant PFAS in the environment.

TFA also enters the environment via several fluorinated gases, pharmaceuticals, industrial chemicals and the direct release of industrially produced TFA. Despite its prevalence, routine PFAS tests do not include TFA.

Short-chain PFAS, unlike long-chains, are extremely mobile in water systems, moving more easily through the environment once they enter it. This increased mobility explains why short-chain PFAS have already been detected in remote areas like Antarctica.

TFA’s short structure also makes it difficult to remove from water. Cullens-Nobis said, “It is extremely difficult to remove from water because it is such a small molecule. It’s really expensive, high energy and just not practical to do yet.”

Filtration is often used as a mitigation strategy for water contaminated with long-chain PFAS; that’s not the case for short-chain PFAS.

TFA is not thought to be bioaccumulative like the legacy PFAS. “However, we don’t know the impact of continuous exposure over decades. And most of the research has been short-term on laboratory animals. And again, they’re not seeing significant health impacts, but I would look for more press, more research on TFAs in the coming years,” said Cullens-Nobis.

Avoiding short-chain PFAS is harder than it sounds. Many state laws define PFAS as a chemical that contains at least one fully fluorinated carbon atom. By federal standards, two fluorinated bonds are needed to be considered PFAS.

For example, in Minnesota, if a farm uses the EPA’s definition, there are only six active ingredients that contain PFAS. However, if they use the state of Minnesota’s definition, there are 97 pesticide active ingredients that contain PFAS. The gap between state and federal definitions leaves farmers with no clear standard to follow.

“Definition is really important when we think about regulating PFAS as a class of chemicals. How PFAS are defined will impact which chemicals are subject to regulations,” Cullens-Nobis said.

by Sonja Heyck-Merlin