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Causation Issues in PFAS Litigation: Where Did the “Forever” Chemical Come From?

Causation Issues in PFAS Litigation: Where Did the “Forever” Chemical Come From?

By Adam M. Dinnell and Bryan Zubay

Per- and poly-fluoroalkyl substances, also known as PFAS, are synthetic, broadly used chemicals. Frequently referred to as “forever chemicals,” they have been subjected to rigorous scrutiny by the Environmental Protection Agency, other governments and agencies, and litigants.[1]

The EPA recently designated PFAS as hazardous substances,[2] exposing manufacturers to potential cleanup costs. Beyond this increased regulation, the litigation landscape continues to evolve dramatically. Lawsuits, including for alleged injurious exposures, have increased exponentially, with more expected in the future. With some commentators already referring to PFAS as “the mother of toxic torts” and the “next asbestos,”[3] it makes sense to move beyond whether PFAS litigation is here to stay (it is) and consider what the contours of this litigation will look like.

Specifically, how will parties attempt to prove or defeat causation? Veterans of asbestos litigation will recall interminable depositions, with dozens of defendants asking plaintiffs rote questions about whether they remembered encountering that defendant’s products. Will new science surrounding PFAS change the calculus? The answer is likely yes. Developments in PFAS tracking research and technology may dramatically affect how parties can prove or disprove causal links between parties and their chemicals.


PFAS were developed in the 1930s, and over the course of the 20th century became nearly ubiquitous due to their remarkable ability to make surfaces resistant to oils and wrinkles. They are broadly present in consumer goods, including food packaging, clothing, furniture fabrics, and nonstick cookware, as well as firefighting foams.[4] Humans ingest them through food, drinking water, and household dust.[5]

As their use has grown, so have concerns about potentially negative health effects for humans and the environment.[6] The EPA has issued health advisories regarding safe and unsafe quantities of PFAS since at least 2016, but revised those advisories this year to indicate that PFAS may cause health risks at far lower concentration levels than previously thought: 0.004 parts per trillion, rather than 70 ppt.[7]

Different carbon-fluoride bond structures result in different types of PFAS, numbering over 12,000 known today.[8] According to some, various PFAS have been linked to obesity, birth defects, altered metabolism, fertility issues, ulcerative colitis, high cholesterol, development toxicity, liver hypertrophy, thyroid disease, and various types of cancer, including non-Hodgkin’s lymphoma, breast, liver, kidney, testicular, prostate, and ovarian cancers.[9] Others are considered relatively harmless.[10]

The EPA’s Proposed Rule and Ongoing Litigation

On August 26, 2022, the EPA proposed a new rule that would classify two widely used PFAS chemicals as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (“CERCLA” or “Superfund”), which could expose manufacturers and users of PFAS to liability for PFAS dissemination and cleanups. The EPA touts the rule as “increas[ing] transparency around releases of these harmful chemicals and help[ing] to hold polluters accountable for cleaning up their contamination.”[11]

The proposed rule is, according to the EPA, prompted by new data and analysis suggesting that the levels at which PFAS may cause adverse health effects are significantly lower than previously understood.[12]The CERCLA designation would require any person in charge of a vessel or facility to report releases of PFOA and PFOS of one pound or more within 24 hours of the release. It would also require that federal agencies disclose the presence on the premises of hazardous substances, including PFOA and PFOS.[13]

The proposed regulation comes amidst a dramatic growth in the breadth and depth of litigation against corporations that have extensively used PFAS in manufacturing, as well as expansion of the types of parties who bringing such lawsuits—from individuals to municipalities and states.[14] One federal judge presiding over multidistrict litigation pertaining to PFAS has pointed out that such litigation poses “an existential threat” to such massive corporations as 3M and E. I. du Pont de Nemours and Co.[15]

For example, the Commonwealth of Massachusetts has sued 13 companies, including 3M and Du Pont, for violations of the Safe Drinking Water Act and Massachusetts Consumer Protection Act, as well as common law product liability, negligence, public nuisance, and trespass claims.[16] The Kalispel Tribe of Indians sued 3M Co., Tyco Fire Products LP, and the United States, alleging fire-suppressing foam has tainted their drinking water.[17] The City of San Diego has sued more than 20 chemicals companies for “manufacturing and steadfastly concealing the toxic nature of firefighting foams that have contaminated drinking water supplies around San Diego for decades.”[18]

Tracking Where PFAS Comes From

Historically, plaintiffs alleging damages based on contamination with hazardous substances (most familiarly, asbestos) have asserted various theories of liability when it is impossible to identify the specific manufacturer or supplier of the hazardous substance.[19] As commentators observed years before the EPA’s proposed rule, CERCLA’s imposition of joint and several liability among responsible parties could put chemical companies sued for contamination in the unenviable position of having to prove that they did not manufacture any of the PFAS at the alleged site.[20]

As litigation concerns and regulations relating to PFAS expand, so have efforts in the field of environmental forensics to track PFAS to their source.[21] Tracking PFAS is complicated by the fact that the types of PFAS in a given product are typically proprietary information. Nonetheless, information gleaned from the types and percentages of PFASs found in a given sample may allow researchers to identify the manufacturing process or originating product. Whether the composition of a PFAS molecule is “branched” or “linear,” the distribution of consecutive perfluorinated carbons and the formation at the end of a given PFAS chain can indicate what manufacturing process originating that molecule.[22] These data points collectively can give an imperfect “fingerprint” identifying the manufacturing process that sourced the contaminant, providing litigants with more information to use in arguing for or against the allocation of responsibility.

As scientists have explained, multiple lines of evidence can be pieced together to identify the sources of the PFAS that are identified—whether it be in the water, sediment, or soil.[23] No one tool can be used to uncover their sources, but it can be done using a holistic course of scientific action.[24] This includes a combination of analytical chemistry, PFAS fate and transport, analysis of site-specific conditions, graphical analysis, and statistical methods.[25] This will require counsel to engage a multidisciplinary expert team that covers chemistry, hydrogeology, and fate and transport.

As the environmental forensics methods for tracking PFAS continue to develop, litigants will need to understand these methods as they consider how to prove or disprove liability and causation. Now that it is clear PFAS litigation is here to stay, this type of scientific evidence will be key in the years to come.




















[20] See, e.g.,






Adam Dinnell is a partner and Bryan Zubay is an associate at Hicks Johnson PLLC, a Houston-based trial law firm.