Long-lasting synthetic chemicals called PFAS persist through wastewater treatment at levels that may affect the long-term feasibility of irrigation using treated wastewater, according to a study conducted by researchers at Penn State and recently published in the Agronomy Journal.
Per-and polyfluoroalkyl substances, often referred to as “forever chemicals,” form a group a more than 4,700 synthetic compounds. They are used to make fluoropolymer coatings and products that resist heat, oil, stains, grease and water, and are found in a variety of products from clothing and furniture to food packaging and nonstick cooking surfaces.
“PFAS are so pervasive and persistent that they have been found in the environment all over the world, even in remote locations,” said Heather Preisendanz, associate professor of agricultural and biological engineering at Penn State. “Unfortunately, these compounds have been shown to negatively impact ecological and human health, particularly because they can bioaccumulate up the food chain and affect development in children, increase risk of cancer, contribute to elevated cholesterol levels, interfere with women’s fertility, and weaken immune systems.”
Because of their wide variety of uses, PFAS enter wastewater treatment plants from both household and industrial sources, said Preisendanz.
Beneficial reuse of treated wastewater is an increasingly common practice in which treated wastewater is used for irrigation and other non-potable purposes.
According to Preisendanz, this practice provides an opportunity for the soil to act as an additional filter for PFAS, reducing the immediate effect of direct discharge of PFAS to surface water, as would typically happen following traditional wastewater treatment.
However, given that the chemical structures of PFAS are difficult to degrade, the risks and potential trade-offs of using treated wastewater for irrigation practices, especially over the long term, are not well understood.
“PFAS have been shown to be taken up by crops and enter the food chain when the crops are consumed, so when treated wastewater is used for irrigation activities in agricultural fields, understanding these trade-offs is of critical importance,” she said.
Preisendanz and her colleagues analyzed PFAS concentrations in water that passed through a water reclamation facility. They collected bimonthly water samples from fall 2019 through winter 2021 prior to treatment and after treatment.
Since the treated water from the wastewater treatment plant is used to irrigate nearby crops, the team also collected tissues from those crops, including corn silage and tall fescue, to assess the presence of PFAS.
The team identified 10 types of PFAS across the site, with average total measured concentrations of 88 nanograms per liter in the wastewater effluent and concentrations as high as 155 nanograms per liter in the downstream monitoring wells.
The conclusions suggest that occurrence of PFAS across the site is nearly ubiquitous and that levels increase with the direction of groundwater flow.
The EPA recently said two of the most PFAS are a risk to human health at any detectable level.
“This presents potential challenges for beneficial reuse of wastewater,” Preisendanz said.
While the groundwater near the spray-irrigation site the team studied is not used for drinking and not likely to pose a risk to human health in that regard, the team did find several PFAS compounds in crop tissue samples collected at both irrigated and nonirrigated portions of the site.
“This suggests that PFAS may enter the food chain when these crops are fed to livestock,” Preisendanz said, adding that future research is needed to determine potential risks to livestock health and the potential implications of PFAS presence in meat and dairy products.
This research was funded in part by the Penn State Office of the Physical Plant, USDA Agricultural Research Service, the USDA National Institute of Food and Agriculture, Environmental Protection Agency, and the Penn State Institutes of Energy and the Environment.