Scientific Reports & Articles

Sludge in the Garden: Toxic PFAS in home fertilizers made from sewage sludge

This study by the Sierra Club is an important one because it alerts plant lovers that they are putting toxic substances in their gardens and homes. It’s also important because it explains why you have to include “precursor chemicals” when doing any analysis for PFAS. Precursor chemicals change and combine over time to become PFAS. So, if those chemicals are present, you can expect the amount of PFAS in that soil to actually increase over time.

It is also important because it provides us with a real-time case study of how the industry responds to science it doesn’t like.

In the backwoods of the MABA website there is this document from June 2021 that appears to have been written for members only, but which somehow made it onto a public link. It contains criticisms of the Sierra Club study and has a list of recommended talking points for responding to the media or to anyone else who asks. These public-relations talking points came from a memo drawn up by Dana Garvey, of Garvey Resources, Inc. , a self-described “environmental consulting firm that specializes in Biosolids Consulting.”

The talking points and the criticism rely on the same arguments we see echoing across the industry
a) Sure, biosolids have PFAS in them, but only in tiny amounts, and
b) PFAS are everywhere and you’re exposed all the time, so who cares? and
c) if you or you family are sick from PFAS exposure, it can’t be from biosolids, it has to be from house dust or dental floss.
Also mentioned in the response document is Dr. Sally Brown. (See more about her work and these pervasive talking points on The Industry page).

The industry and its federal regulator, the EPA, have known for a long time that sewage sludge was too toxic to use as fertilizer for our food, but they have continued to promote the practice.

Starting in the 1970s and continuing into this century, Dr. Donald Lisk, who was director of the toxic chemicals laboratory at Cornell University, conducted numerous studies that showed the transfer of toxic substances from sludge-amended soil to crops and livestock.

In 1981, he was quoted in this NY Times article, Permanent Ban Urged on Sludge in Farming, as saying ''Sludge is the product of practically everything in our society, and may contain virtually any element and a galaxy of dangerous chemicals, depending on the spectrum of industries in the area. It's just too poisonous and unpredictable to use on land.'' He said farmers should not use it, the state should permanently ban its use on farmland, and it should be incinerated. (New York resumed spreading sludge after the 1988 Clean Water Act banned ocean dumping.)

For a sampling of the innumerable studies showing harmful effects, see this SourceWatch page: Scientific Studies of Sewage Sludge. This collection of about 70 studies and articles runs from 2006 to 2012.

In 2009, the EPA did its own large-scale testing and analysis of samples, the Targeted National Sewage Sludge Survey (TNSSS). Their results confirmed the warning issued by Dr. Lisk (above), decades prior, finding that all sludge had toxins in it. EPA published the findings but took no regulatory action to stop sludge-spreading. A summary of results and a list of chemicals, metals, pharmaceuticals, steroids, hormones, semivolatile organics, flame retardants, pesticides, and PFAS can be found HERE.

The sludge industry has had many decades to solidify its hold on regulators and expand its funding of research. EPA whistleblower Dr. David Lewis gives a detailed explanation of how this process works in his 2014 book Science For Sale.

Nonetheless, some good science is still available, mostly focused on the dangers of PFAS — an eventuality that seems to have caught the sludge PR machine a little flat-footed. PFAS has so far been linked to liver damage, thyroid cancer and other cancers, and low sperm counts. A 2024 article from Science predicts that 80 million people in the U.S. are currently relying on PFAS-contaminated well water for their drinking water. But new data in 2025 reveals that the number is actually more like 172 million people.

For a more in-depth understanding of PFAS, view this 2024 webinar featuring toxicologist Joe DiNardo.

The problem of what to do with sewage sludge will not be solved with new ways to remove toxins at the wastewater treatment plant. While innovations on that front may provide some band-aids, a real, long-term solution will only come by dealing differently with waste at the source of its production and rethinking our centralized, water-based waste systems.

Centralized sewer systems — that is, using great quantities of clean drinking water to bring any and all municipal, industrial, and street waste to a single place — is one half of the problem. Unspooling these complex systems will take time, but the technology for alternative systems already exists. An alternative, decentralized system would rely on large and small-scale composting toilets for residential and commercial waste, with industrial waste being handled by a combination of on-site composting, recycling, and treatment.

For a description of how composting toilets work and to see examples, visit the Clivus Multrum website. For a detailed understanding of why this change is needed and how it would work, see this 2002 article “Sewers, Sewage Treatment, Sludge: Damage Without End,” by Abby Rockefeller.

In the short term, options for dealing with this mixed, centralized waste are not great. Putting sludge into landfills instead of spreading it on farmland is an immediate, necessary Step 1. But the leachate from landfills is usually trucked to wastewater treatment plants, which creates an increasingly-toxic loop. Stopping, or at least meaningfully limiting, the production of toxic chemicals is work that needs to be done in parallel with addressing sludge at wastewater treatment plants.

In the intermediate term, however, there is a not-so-terrible option called “supercritical water gasification,” in which sludge is heated to the point at which everything — even the complex toxins — in it break down into elemental components of hydrogen, carbon dioxide, and water. Research on this process has been going on for years, and has progressed to pilot-scale projects that yield promising results.

Another research track has been focused on breaking the tenacious fluorine bonds in PFAS through chemical means. A big step forward was announced in June of 2025, in which researchers developed a catalyst that can break the bonds at room temperature.

The other half of the problem is the long list of poisons that our industrialized society dumps into the waste stream. As we change how we treat waste, we’ll simultaneously need to change what is acceptable to put into that waste. Science will have to abandon the pursuit of man-made materials and chemicals that defy nature and instead embrace a nature-based paradigm in which all materials are ephemeral and subject to nature’s rules of recycling.