Researchers Target PFAS in Agricultural Runoff

Over half of the U.S. by area— nearly 485 million ha (1.2 billion ac) — consists of farmland, U.S. Department of Agriculture (USDA). Although this land is vital to the U.S food supply and economy, it also represents a significant source of water pollution.

The U.S. Geological Survey’s National Water-Quality Assessment Project identifies agricultural runoff as the leading cause of water quality issues in rivers and streams, the third-leading cause in lakes, and the second-largest source of wetland pollution due to farming’s extensive soil disturbance and contributions of sediment, pesticides, and herbicides into stormwater runoff. 

Researchers and regulators are placing new scrutiny on the presence of per- and polyfluoroalkyl substances (PFAS) ­— a group of synthetic chemicals that resist breaking down in the environment — in agricultural runoff.

Understanding PFAS in Agriculture

PFAS in agricultural soil can pose a serious risk to human health by seeping into groundwater, contaminating drinking water sources — a particular concern for the 23 million U.S. households that rely on private wells.

The USDA has identified several common sources of PFAS in agricultural soil. They include

• aqueous film-forming foams, commonly used by airports and military bases to control fuel fires, which often introduce PFAS onto nearby farms;
• PFAS-contaminated biosolids used as fertilizers;
• discharges from nearby factories or facilities using PFAS in manufacturing processes; and
• irrigation with water drawn from PFAS-affected sources.

In April 2024, the U.S. Environmental Protection Agency (EPA) set national drinking water limits for six PFAS chemicals, which apply to public water systems in all 50 states. However, since PFAS exposure on farms and in agricultural products can vary from EPA standards, state agencies may set their own limits for agricultural samples, such as soil, water, dairy, and beef.

Beating PFAS With Biochar

Scientists are working to help farmers and other stakeholders overcome PFAS challenges in agricultural soil by developing strategies to reduce their impact. A 2024 study, published in Science of the Total Environment, states that biochar — a stable, solid, carbon-rich material made from organic waste that is heated in the presence of limited oxygen — offers potential for PFAS remediation in agricultural settings. Biochar works by trapping PFAS in the soil, keeping them from spreading or being absorbed by living things.

Biochar consists of materials like crop waste, wood, or manure, and its ability to trap PFAS varies based on these materials and the temperature used during production. Higher temperatures usually create biochar with more surface area and water-repelling properties, which improves its ability to remove PFAS, the study demonstrates.

Besides removing PFAS, biochar offers environmental benefits like storing carbon, improving soil quality, and recycling waste materials from farms and industries.

Users can apply biochar in various ways. When mixed with contaminated soil, it reduces PFAS mobility and bioavailability, minimizing plant uptake and leaching into water systems. In water filtration, biochar-based systems effectively lower PFAS levels in irrigation water before use. Additionally, incorporating biochar into biosolid treatments can trap PFAS, preventing their release into the soil during application.

Compared to traditional adsorbents like activated carbon or ion-exchange resins, biochar is a more cost-effective and eco-friendly option, according to USDA scientists Pia Ramos and Daniel Ashworth, who led the study. Its production requires fewer resources and has a smaller ecological footprint. The study also states that while activated carbon and resins may perform better at removing short-chain PFAS, biochar’s versatility and sustainable lifecycle make it an ideal choice for agricultural use.

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