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6 things wastewater treatment plant owners need to know about PFAS

September 21, 2022

By Krista Barfoot and Angus McGrath

PFAS in wastewater can adsorb to biosolids or be transported in effluent. So, regulators are increasingly focused on wastewater treatment plants.

In our work, we have heard it many times: “Do we need to be concerned about PFAS coming from wastewater treatment plants (WWTPs) and passing into the environment?”

You’ve no doubt heard of PFAS—the so-called “forever” chemicals. These per-and polyfluoroalkyl substances are a class of human-made, fluorine-containing chemicals that are extremely persistent in the environment and pose human and environmental health risks.

Regulators are increasingly concerned about the role that wastewater treatment plants (WWTPs) play in the cycling of these chemicals. While PFAS mitigation so far has focused on sources that contaminate drinking water supplies, WWTPs have been identified as potential pathways for PFAS release to the environment.

Since WWTPs can accept wastewater from residential, commercial, and industrial sources, we know PFAS can potentially flow into a plant and flow out as effluent. Some PFAS will also adsorb to the biosolids (aka sludge) in the plant and potentially be spread as fertilizer on agricultural fields. This raises the potential for PFAS to impact potable water supplies or be absorbed by plants and carried up the human food chain.

So far, nothing in the standard water treatment process within WWTPs addresses PFAS concentrations. The potential implications are significant for WWTP owners. In addition to liability issues, WWTP owners need to be concerned about how they will manage biosolids in the future and how PFAS-containing effluent may pass through the WWTP and travel downstream.

In considering these implications, here are six things WWTP owners need to understand about the emerging PFAS science, regulatory issues surrounding PFAS, and potential impacts to the human water supply or food chain.

When PFAS-containing wastewater comes into a treatment plant, there is typically nothing within the standard treatment process that would address PFAS concentrations.

1. Research showing PFAS in biosolids

As we’ve noted in previous blogs, PFAS are organic chemicals first developed in the late 1930s for a large suite of industrial and commercial applications. With their combined water- and oil-resistant properties, PFAS are used as resistant coatings for heat, oil, grease, and stains. They are used in firefighting foam, textile coatings, food packaging, and other applications.

While there are thousands of chemicals in this class, perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) are the most well-known, researched, and understood.

How do these chemicals get to WWTPs? Plants can accept wastewater from a suite of sources, including residential, commercial, and industrial sources, as well as potentially leachate from landfills and run-off from airports and other properties.

Because PFAS are so prominently used in industrial processes, we know there’s potential for PFAS to be in industrial wastewater. But since PFAS are also present in so many of our commercial and household products, we can expect PFAS to exist in other types of wastewaters as well. When they enter a plant, we can expect some PFAS will adsorb to biosolids.

Studies show that PFOS and PFOA are, indeed, showing up in biosolids. A 2020 review of 40 different studies revealed that PFOS and PFOA concentrations are consistently detected in biosolids around the globe. The studies showed the highest concentrations in biosolids produced in China—likely reflecting that China is one of the largest manufacturers and consumers of PFAS. Studies found the lowest concentrations in Africa, perhaps reflecting more limited PFAS use.

2. How PFAS in biosolids get into soils

The same studies cited above show some WWTPs produce biosolids with very elevated PFAS concentrations. When biosolids from WWTPs are applied to land, these PFAS are passed into the environment. Indeed, studies that examined PFAS concentrations in soil—to which biosolids and other amendments were applied—often show greater PFAS concentrations than those observed in background soils.

Also, soil that has been amended with industrially derived biosolids indicates greater PFAS concentrations than soil amended with municipally derived biosolids. However, a 2017 Canadian study showed elevated soil concentrations may not always occur with biosolids applications.

What do these studies mean for WWTPs? It means WWTP owners, both in the public and private space, will need to pay attention to the evolving regulations and consider their own potential to serve as a means of PFAS release to the environment.

Some PFAS in the wastewater stream will adsorb to the biosolids and potentially be spread as fertilizer on agricultural fields.

3. State and local regulations take aim at biosolids

Local and state government entities are already taking action. In July 2020, the California State Water Resources Control Board put an order out to publicly owned treatment works (POTW) because of concerns around the potential for WWTPs to function as a route for PFAS discharge to the environment. This order noted the potential for these works to discharge PFAS to the environment—including through biosolids—and required sampling of biosolids for PFAS.

In March 2019, Maine created a requirement for testing biosolids for PFAS prior to land application. More recently though, Maine passed legislation prohibiting all municipal biosolids land application even if the state screening levels are met.

On a municipal level, in December 2019, Pima County in Arizona fully suspended the land application of biosolids over concerns around PFAS. The county lifted the ban in late 2020, but it serves as another example of governments acting on PFAS in biosolids.

4. Federal regulations have significant implications

In the US, the Environmental Protection Agency (EPA) has proposed listing PFOS and PFOA as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). One major implication of the listing would be release reporting requirements for facilities where PFOS and PFOA have been deposited, stored, disposed of, placed, or otherwise located. WWTPs could be included in these reporting requirements.

It is also expected that the designation of PFOS and PFOA as hazardous substances under CERCLA will have implications for states, as they sometimes include federally designated hazardous substances within their state clean-up regulations.

In Canada, in April 2021, the federal government released a Notice of Intent to address PFAS as a broad class, as opposed to taking a substance-specific management approach. These activities could change the regulatory status of PFAS and lead to a variety of new requirements for the assessment and management of these compounds.

Could PFAS in biosolids also be taken up by plants or livestock and enter the food stream? There is a chance.

5. PFAS and human water and food exposure

PFAS are soluble and mobile, so there is an inherent risk that PFAS in land-applied biosolids could migrate to the water table and impact drinking water supplies. Given the release of new interim Health Advisories (HAs) by the US EPA in June 2022 for PFOA and PFOS that are many orders of magnitude lower than the previous HAs, it is easy to project that even limited concentrations of PFAS in biosolids could produce concentrations in groundwater that exceed the interim HAs.

Could PFAS in biosolids also be taken up by plants or livestock and enter the food stream? There is a chance. Let us consider what this could mean for food production.

Research has shown that plants can take up PFAS from soil, and higher soil concentrations do lead to greater PFAS uptake. This uptake, and the distribution of PFAS to edible plant parts, is influenced by many factors. These include external factors like PFAS properties (such as chain length or functional group) and soil properties (like soil organic carbon content), as well as internal factors such as plant properties (like protein content, root system) and plant organ properties (such as partitioning within plant).

For example, root vegetables like carrots—which roots primarily serve to absorb nutrients—tend to have much higher concentrations of PFAS than other vegetables, such as potatoes, whose roots primary function as storage. That said, the root peel in potatoes can serve as an important reservoir for PFAS. One study indicated potato peels contain about 2.3 times the concentration of PFOA and 21 times the concentration of PFOS as the peeled tubers.

Further research is needed to better understand and manage the potential for PFAS-containing biosolids to impact the food stream. As a means of making decisions around biosolids use, we need to confirm how food concentrations are correlated to the use of biosolids.

PFAS in biosolids can be taken up by plants or livestock and then enter the food stream.

6. How do we potentially address the problem?

As we’ve mentioned, not all biosolids are created equal. While biosolids can have elevated levels of PFAS, they don’t all necessarily have those levels. What does that mean?

Well, a broad sweeping approach to managing PFAS in biosolids is not likely appropriate. Instead, WWTP owners should consider targeted approaches that begin with an assessment of the sources of the wastewater that feed into each WWTP—and the potential for elevated PFAS within those sources.

In the end, controlling PFAS concentrations in biosolids may, in part, come down to managing the waste inputs. This approach could include setting PFAS limits on industrial discharges to sewage treatment plants (an approach previously used by the US EPA for metals).

If the sources feeding into the WWTP suggest potential for elevated PFAS concentrations, operators may consider influent sampling to determine whether further action is warranted to prevent environmental releases. This could mean further testing of effluent and sludge or modifying plants to address PFAS within the waste stream.

Within any of these steps—from source assessment to testing to treatment—our Company can help. Our experts are working hard to understand emerging PFAS science and regulations and bringing PFAS solutions to our clients and their customers.

  • Krista Barfoot

    Focused on strategic site planning, vapor intrusion assessment, and risk assessment and management, Krista has worked on chemistry, toxicology, geology, and ecology projects on several large, high-profile brownfield sites in Ontario.

    Contact Krista
  • Angus McGrath

    A principal geochemist and expert in remediation efforts, Angus has spent his career researching and cleaning up human impacts on the natural world.

    Contact Angus
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