RESEARCH MEMORANDUM

RE: PFAS Exposure Pathways in Aqueous Film-Forming Foam (AFFF) — Plaintiff Science, Recent Developments, and Litigation Strategy

MDL Reference: In re Aqueous Film-Forming Foams Products Liability Litigation, MDL No. 2873 (D.S.C., Hon. Richard M. Gergel, Master Docket No. 2:18-mn-2873-RMG)

A note on MDL numbering: Several intake materials we have reviewed identify the AFFF litigation as MDL 2433. MDL 2433 is In re E. I. du Pont de Nemours and Co. C-8 Personal Injury Litigation, S.D. Ohio (closed after the 2017 DuPont/Chemours settlement). The active AFFF MDL is 2873. Both are discussed below because the evidentiary record and "probable link" findings developed in the C-8 cases (Wood County, WV) are now being extended, contested, and refined inside MDL 2873.

Date: May 2026

Classification: Background research brief — not legal advice. All citations are primary-source where available; where a claim rests on a secondary source the secondary is identified expressly. Sources verified through publicly accessible URLs at the dates indicated.

EXECUTIVE SUMMARY

The AFFF litigation has reached an inflection point. As of early 2026, approximately 15,200 active personal-injury filings are pending in MDL 2873 (with a documented late-September 2025 filing surge that prompted Case Management Order 35 to pause intake for documentation verification). Case Management Order 33 narrowed compensable injuries to six categories: kidney cancer, testicular cancer, liver cancer, thyroid cancer, thyroid disease, and ulcerative colitis. The first personal-injury bellwether trial — focused on kidney cancer — was vacated from the October 2025 docket under CMO 35 (Aug 15, 2025), and Judge Gergel held a Science Day on June 20, 2025 covering liver and thyroid cancer.

Three independent developments in 2023–2025 have changed the plaintiff calculus:

1. IARC reclassified PFOA as Group 1 (carcinogenic to humans) at its Working Group meeting in Lyon, 7–14 November 2023, with summary findings published in The Lancet Oncology on 30 November 2023 and the full IARC Monograph Volume 135 published in February 2025. PFOS was classified as Group 2B. The classification is based in part on "limited evidence" in humans for renal cell carcinoma and testicular cancer (IARC, 2025).
2. EPA finalized the National Primary Drinking Water Regulation for six PFAS, with enforceable MCLs of 4.0 ng/L for PFOA and PFOS, on April 10, 2024, with publication in the Federal Register on April 26, 2024 (89 Fed. Reg. 32,532; effective June 25, 2024).
3. Half-life science has narrowed. The Veneto longitudinal cohort (Batzella et al., 2024) reports a mean PFOA serum half-life of 2.36 years — shorter than the 3.5 years in Olsen et al. (2007), with female-specific values as low as 1.64–2.04 years. The shift carries direct implications for statute-of-limitations briefing, dose-reconstruction, and exposure-window arguments that defendants have used to attack temporality.

Defendants are now organized around a counter-narrative — "the C-8 Science Panel's probable links no longer reflect the state of the science" — articulated most clearly in Boston et al. (2025) in Frontiers in Public Health, written by paid defense consultants. Plaintiff teams must read that paper carefully, because it is the spine of the Daubert challenges already filed and the cross-examination outline the defense will use at every bellwether.

The biggest open exposures in current plaintiff filings are: (a) inconsistent exposure-reconstruction methodologies across firms; (b) under-developed differential-diagnosis records in firefighter-cohort kidney cancer cases; (c) non-uniform handling of mixed AFFF/PFAS and non-AFFF/PFAS sources in occupational and water-contamination cases; and (d) statute-of-limitations exposure where states have not adopted discovery-rule equivalents and where revised half-life data shortens the window in which serum biomarkers can support a "continuing exposure" argument.

This memorandum walks through the underlying chemistry and toxicology, the most recent peer-reviewed studies, the regulatory record, defense expert positioning, and concrete litigation gaps with strategic implications.

1. THE PRODUCT AND THE EXPOSURE PATHWAYS

1.1 What AFFF is

Aqueous film-forming foam is a fire-suppression agent developed jointly by the U.S. Naval Research Laboratory and 3M in the late 1960s. AFFF works by forming a thin aqueous film over hydrocarbon fuels — the film is what gives the foam its distinctive ability to suppress liquid-fuel fires. The film-forming behavior depends on perfluoroalkyl surfactants, historically PFOS- and PFOA-based, which are the chemistries now at the center of the litigation. After the 3M voluntary phase-out of PFOS production (2000–2002), industry shifted to fluorotelomer-based AFFF (often "C-6" chemistries), which break down in the environment and in living tissues into a range of related PFAS. Plaintiff toxicology should not assume "C-6 = safe"; environmental persistence and bioaccumulation of telomer breakdown products are well documented (ITRC, 2023).

The federal specification (MIL-F-24385F, 1969 onward; superseded in 2023 by MIL-PRF-32725 for fluorine-free foam) required film-forming performance that effectively mandated PFAS chemistry until DoD published its non-PFAS performance specification (DoD, 2023).

1.2 Routes of exposure

For the firefighter and military cohort:

• Dermal contact during foam-handling, equipment maintenance, and gear contamination (turnout gear that has been exposed to AFFF retains measurable PFAS even after laundering).
• Inhalation of aerosols during deployment, training burns, and apparatus testing.
• Incidental ingestion during deployment, hand-to-mouth contact, and consumption of food or water on contaminated sites.
• Hand transfer from foam-coated surfaces to gear, helmets, and fabric.

For the surrounding-community cohort:

• Drinking water from groundwater contaminated by historical AFFF use at fire-training pits, hangars, airports, and military bases. Hundreds of public water systems near such sites have tested above the new EPA MCLs.
• Soil and dust in the immediate vicinity of training areas.
• Local-fish and game ingestion for some communities.

A 2023 systematic occupational study of four U.S. fire departments reported that geometric-mean serum PFHxS levels in male firefighters were significantly elevated relative to NHANES referents, and branched PFOS isomers (Sm-PFOS) were elevated in all four departments studied (Trowbridge et al., 2023). The persistence of PFHxS — with reported half-lives of 5.7–8.5 years in adults — is particularly relevant when the litigation cohort includes firefighters who left active duty more than a decade before diagnosis.

1.3 Bioaccumulation and tissue distribution

PFOA and PFOS are primarily plasma-bound; they bind to serum albumin and to fatty-acid binding proteins. Their accumulation does not follow the classic lipophilic-organic-pollutant pattern (i.e., they are not stored primarily in adipose tissue). Instead, they accumulate in liver, kidney, and serum, with smaller fractions in lung and bone. The kidney's role in PFOA elimination — through saturable renal resorption — is the mechanistic basis for both the long human half-life relative to other species and the kidney-specific cancer signal. (Olsen et al., 2007; ATSDR, 2021.)

This mechanism matters at trial: defense experts routinely point to rodent peroxisome-proliferator-activated-receptor-alpha (PPARα) effects as "rodent-specific," arguing that human relevance is overstated. The kidney-resorption pathway is human-specific in kinetic profile and is independent of PPARα — this is a structural reason to expect that human kidney burden is not adequately predicted by PPARα-mediated rodent models alone. IARC's 2023 working group reviewed this mechanism in its evaluation (IARC Monograph Vol. 135, 2025).

2. CURRENT STATE OF PLAINTIFF SCIENCE

2.1 The C-8 Science Panel as the foundation

The C-8 Science Panel was established in 2005 under the Leach v. DuPont class settlement (Wood Cir. Ct., W. Va., Civ. Action No. 01-C-608). Its mandate was to determine whether there was a "probable link" — defined in the settlement as "more likely than not" — between PFOA exposure and any human disease. In 2011–2012, the Panel found probable links for six conditions: diagnosed high cholesterol, ulcerative colitis, thyroid disease, testicular cancer, kidney cancer, and pregnancy-induced hypertension/pre-eclampsia. The Panel published peer-reviewed work supporting each link, including Steenland and Woskie (2012), which reported elevated kidney cancer mortality in the highest cumulative-exposure quartile (SMR = 3.67, 95% CI 1.48–7.57; lagged-exposure analysis, n = 11 deaths) in the DuPont worker cohort, and Vieira et al. (2013) in Environmental Health Perspectives, which reported adjusted odds ratios of 2.0 for kidney cancer in the high (95% CI 1.3–3.2; statistically significant) and very high (95% CI 1.0–3.9; borderline) modeled-serum-PFOA quartiles among the most-exposed Mid-Ohio Valley residents.

Six of those probable links are not, in themselves, dispositive of any AFFF claim — but they form the scientific backbone for general causation arguments. Of the six CMO-33 disease categories in MDL 2873, three correspond directly to C-8 Panel findings (kidney cancer, testicular cancer, ulcerative colitis), one is closely related (thyroid disease), and two extend beyond C-8 (liver cancer, thyroid cancer).

2.2 What has happened since 2012

The most consequential developments for the plaintiff record are these:

IARC (Working Group 2023; Monograph Vol. 135 published 2025) — PFOA as Group 1. The Working Group of the IARC Monograph program met in Lyon November 7–14, 2023, evaluated more than two decades of mechanistic and epidemiological evidence, and classified PFOA as "carcinogenic to humans (Group 1)" and PFOS as "possibly carcinogenic to humans (Group 2B)." A summary of the evaluations was published online in The Lancet Oncology on 30 November 2023; the full Monograph Volume 135 was published by IARC in February 2025. The PFOA classification rests on (i) sufficient evidence in experimental animals, (ii) strong mechanistic evidence in exposed humans for key characteristics of carcinogens (immunosuppression, modulation of receptor-mediated signaling, oxidative stress, and epigenetic alterations), and (iii) limited evidence in humans for renal cell carcinoma and testicular cancer (IARC, 2025, Vol. 135).

The Group 1 classification is highly significant under Federal Rule of Evidence 702 / Daubert analysis. While not dispositive, it shifts the burden of explanation: defendants must now articulate why an IARC Group 1 designation should not inform general causation. The classification is also useful at jury selection and opening — plaintiffs can stand on the same agency that classified asbestos and tobacco smoke as Group 1.

Pooled risk assessment (Steenland et al., 2022). A pooled analysis of the C-8 community cohort and the DuPont occupational cohort estimated a serum-PFOA-versus-kidney-cancer dose-response sufficient to compute attributable-risk fractions at population-level exposures. This work is foundational for the dose-response demonstrations plaintiff experts present at general-causation hearings (Steenland et al., 2022, Environment International).

Recent meta-analyses and community cohorts. Bartell et al. (2025, Journal of Exposure Science & Environmental Epidemiology) reports updated PFOA serum half-lives and dose-reconstruction estimates from the Hoosick Falls / Petersburgh, NY community cohort. Notably, the Bartell paper reports a geometric-mean half-life of 2.86 years adjusted to the Hoosick Falls age distribution, with strong age-stratification (1.96 y under 18; 3.55 y over 60). This is a key recent piece for any plaintiff team building a community-based exposure case. Separately, a 2023 systematic review and meta-analysis (Stratakis et al., 2023, in PMC10627102) reports pooled associations between PFAS exposure and kidney, liver, and testicular cancers, with positive associations strongest in higher-exposure subgroups.

NCI ongoing work. The National Cancer Institute's Division of Cancer Epidemiology & Genetics maintains an active PFAS-cancer research portfolio, including pooled analyses of biomarker-based studies (NCI, 2025). NCI publications carry significant weight on Daubert review because of the agency's institutional independence from both defendants and plaintiffs.

2.3 Half-life science and dose reconstruction

Half-life is doing a lot of work in this litigation. Plaintiffs use back-calculation from current serum levels to estimate historical body burden during the relevant exposure window; defendants attack this back-calculation as speculative.

The most-cited values in older filings come from Olsen et al. (2007, Environmental Health Perspectives), reporting geometric-mean half-lives in 26 retired fluorochemical production workers as PFOS 4.8 years (95% CI 4.0–5.8), PFHxS 7.3 years (95% CI 5.8–9.2), and PFOA 3.5 years (95% CI 3.0–4.1). These values have been load-bearing for plaintiff dose-reconstruction work for fifteen years.

Two recent studies sharpen the picture. Batzella et al. (2024, Environmental Health Perspectives) — a longitudinal analysis of 5,860 highly exposed subjects from the Veneto Region (≥14 years old, with two blood samples 2017–2022), plus a separate analysis of 480 children under 14 — reports a mean PFOA half-life of 2.36 years (95% CI 2.33–2.40) overall, 2.83 years for men, 2.04 years for women, and 1.64 years for children under 14. Pregnancy and lactation accelerated elimination further (1.78 years for women experiencing childbirth during follow-up vs. 2.54 years for women without childbirth during follow-up). Bartell et al. (2025) reports an age-stratified GM half-life of 2.86 years overall (Hoosick Falls–distribution adjusted), ranging 1.96–3.55 years across age strata. A systematic review (Li et al., 2022/2023) places the range of estimated PFOA half-life from 1.48 to 5.1 years, and total PFOS from 3.4 to 5.7 years.

What that means for this litigation:

• Dose-reconstruction back-calculations using a 3.5-year PFOA half-life will, if uncorrected, overstate historical serum levels in female and younger plaintiffs and may understate them slightly in older male plaintiffs at the high end. Defendants will exploit any miscalibration. Plaintiff experts should provide sensitivity analyses across the 1.6–3.5 year range, with primary results using sex-specific and age-stratified estimates.
• The shorter female half-life is also relevant to thyroid and ulcerative colitis cohorts, where female plaintiffs predominate. Cumulative exposure is the relevant integrand, and a shorter half-life implies a shorter biological retention window for any given external exposure.
• For testicular cancer plaintiffs, PFOS half-life (still 3–6 years) is the more relevant species because PFOS — not PFOA — has shown the strongest association with testicular cancer in the recent meta-analyses.

2.4 Dose-response: the under-discussed half of general causation

General causation requires more than "this substance can cause this disease." Under most circuits' Daubert practice, plaintiffs must articulate a defensible dose-response: what level of exposure is sufficient to materially raise the risk of the disease? Recent quantitative risk assessments published in peer-reviewed venues (notably Steenland et al., 2022) provide that anchor for kidney cancer at PFOA serum levels in the range observed in firefighter cohorts and AFFF-impacted communities. Plaintiff teams should mirror this in their expert reports: identify the plaintiff's reconstructed serum exposure, identify the literature dose-response, and articulate the predicted increment in risk.

This is the part of plaintiff briefing that has historically been weakest. Many filings recite "elevated PFAS exposure" without a quantitative serum benchmark and without an explicit dose-response reference. That weakness is what defense Daubert motions are now targeting.

3. RECENT STUDIES (2024–2026): WHAT STRENGTHENS, WHAT WEAKENS

3.1 Studies that strengthen the plaintiff case

• IARC Monograph Volume 135 (PFOA = Group 1, PFOS = Group 2B), Working Group 2023, full Monograph published February 2025. As discussed, this is the single most important external development for general causation since the C-8 Science Panel's findings. IARC's evaluation explicitly cites limited evidence for renal cell carcinoma and testicular cancer in humans.
• Steenland et al. (2022) pooled risk assessment providing a publishable, peer-reviewed dose-response estimate for PFOA and kidney cancer that plaintiffs can cite in expert reports.
• Bartell et al. (2025) Hoosick Falls / Petersburgh community half-life and dose-reconstruction update in Journal of Exposure Science & Environmental Epidemiology, useful both for exposure-reconstruction methodology and as a community-cohort precedent.
• Trowbridge et al. (2020, 2023) firefighter PFAS biomonitoring, demonstrating that firefighters have higher serum PFAS levels than NHANES referents, and identifying AFFF as a significant occupational source. Useful for occupational-cohort general-causation framing.
• Batzella et al. (2024) Veneto half-life data, sharpening sex- and age-stratified half-life estimates and defending plaintiff dose-reconstruction methodology against defense criticism that "Olsen 2007 was a small sample of male workers."

3.2 Studies and developments that weaken — or that defendants will use to weaken — the plaintiff case

• Boston et al. (2025), Frontiers in Public Health. This is the linchpin of the defense narrative. The paper, titled "The evolution of PFAS epidemiology: new scientific developments call into question alleged 'probable links' between PFOA and kidney cancer and thyroid disease," argues that newer studies do not consistently reproduce the C-8 Panel's findings, that improved methodology has weakened the kidney-cancer and thyroid-disease links, and cites Seyyedsalehi & Boffetta (2023) reporting a non-statistically-significant PFOA-specific meta-RR of 1.23 (95% CI 0.99–1.51) for kidney cancer.

Critically — and this is what plaintiff cross-examination must surface — all four authors are employed by Roux, a consulting firm that "provides scientific support to various corporations, law firms, scientific/professional organizations, and the government," the lead author "has been retained as an expert witness on behalf of defendants in various litigation matters regarding exposure to PFAS," and "Roux received partial funding from Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. for the preparation and submission of this manuscript." Plaintiff experts must read the paper and prepare a methodological response — this is not one to ignore.

• The shifting epidemiological landscape generally. Some 2018–2024 cohort studies have not reproduced the C-8 Panel findings, particularly for thyroid disease at lower exposure levels. This is a real signal in the literature; the defense reading is "the link evaporates at population-level exposures." The plaintiff reading is "exposure-response curves often plateau or saturate at high cumulative dose, and the AFFF cohort sits at the high end." Both readings are defensible and the evidence supports a more nuanced framing — but the plaintiff side cannot afford to pretend the negative studies do not exist.
• The Seyyedsalehi & Boffetta (2023) meta-analysis. Anchored at PFOA-specific meta-RR 1.23 (95% CI 0.99–1.51) for kidney-cancer association. The 95% CI crosses 1.0; the defense will cite this aggressively. Plaintiff response should focus on (a) the heterogeneity of exposure quantification across pooled studies, (b) the dose-response observed in the highest-exposure quartiles, and (c) the methodological appropriateness of pooling community cohorts with general-population biomonitoring studies. (Note: the broader PFAS-mixture meta-RR in the same paper, 1.18 [95% CI 1.05–1.32], does reach significance — distinguishing "PFOA-specific" from "any-PFAS" estimates is essential when responding to defense citations of this paper.)
• Mortality cohort studies in Italian PFAS-contaminated regions (Mastrantonio et al., 2024, in Environmental Health) report mixed cancer-mortality results but find elevated all-cause and cardiovascular mortality in the most-exposed areas. The framing is plaintiff-favorable for environmental claims but is more equivocal for individual-causation kidney/testicular cancer cases.

3.3 What the plaintiff side has not yet done well

The peer-reviewed literature of plaintiff-favorable causation is overwhelmingly cohort-level and ecological. Specific causation — proving that this plaintiff's kidney cancer was more likely than not caused by PFOA exposure rather than by smoking, hypertension, obesity, occupational solvents, or genetic risk — is the harder lift. The MDL has not yet developed a uniform specific-causation framework, and individual cases will rise or fall on whether the differential-diagnosis record is rigorous. We discuss this in §5.

4. STATUTE OF LIMITATIONS IMPLICATIONS OF REVISED HALF-LIFE DATA

The half-life science cuts in two directions on limitations:

4.1 The continuing-exposure / continuing-tort theory

In states recognizing a continuing-tort or continuing-exposure theory (or where a discovery rule applies in its full form), plaintiffs argue that biological exposure is ongoing as long as PFAS remains in serum. With Olsen 2007's 3.5-year PFOA half-life, a plaintiff's serum still contains roughly 25% of a 1990s-era body burden in 2025. With Batzella 2024's 2.36-year mean half-life, that same body burden is below 5% at 2025. The shift weakens — in pure mathematical terms — the "continuing-exposure" theory in jurisdictions where the analysis turns on substantial residual body burden.

This is a real exposure for plaintiffs in older firefighter cases. Plaintiff teams should consider:

• Pivoting from "continuing biological exposure" to "delayed manifestation" framing, where the cause of action accrues at diagnosis (or reasonable diagnosability) under the discovery rule, not at last exposure.
• Documenting current-day re-exposure through contaminated water, food, or contaminated turnout gear. Continuing exposure is much easier to prove in firefighters who continued to use AFFF-contaminated gear after their last training-burn deployment, or who lived in a community with a contaminated public water system that has only recently been remediated.
• Distinguishing PFOS and PFHxS from PFOA, since the longer half-lives of PFOS and PFHxS preserve more of the historical body burden.

4.2 The discovery-rule strategy

Most product-liability jurisdictions allow some form of discovery-rule tolling. For PFAS, the threshold question is when a plaintiff's claim accrued — at exposure (rejected in most jurisdictions), at diagnosis, at the point a reasonable person would have connected diagnosis to PFAS exposure, or at the point of public notice that such a connection was scientifically supported. Several recent state-court rulings have anchored discovery to peer-reviewed publications and major regulatory milestones; the IARC Group 1 announcement (Lancet Oncology summary, 30 November 2023) — followed by the full IARC Monograph publication in February 2025 — and the EPA NPDWR (April 2024) are now both available as anchor dates.

For plaintiffs whose diagnoses pre-date the relevant statute period, the strongest discovery-rule argument is now: "A reasonable plaintiff could not have known of the causal link between PFOA exposure and their kidney cancer until IARC's Group 1 classification announcement in November 2023." This is a defensible legal position, and the IARC summary publication is publicly accessible — defendants cannot credibly argue that pre-IARC plaintiffs should have known.

For firefighters in jurisdictions with occupational-disease presumption statutes, the analysis is different. New York firefighter cancer presumption framework — and similar state-level presumption regimes for AFFF/PFAS occupational exposures — modifies the limitations analysis in a plaintiff-favorable way. State-by-state mapping of presumption statutes is essential; specific statutory citations should be confirmed against the current state code and any 2024–2025 amendments before relying on this material in court.

4.3 Dose-reconstruction and backward-extrapolation discipline

Defendants will challenge any dose reconstruction that relies on the older Olsen half-life when the plaintiff is female, young, or had pregnancy/lactation events during the relevant period. Plaintiff experts should:

• Use sex- and age-stratified half-lives derived from Batzella et al. (2024) and Bartell et al. (2025), or comparable.
• Provide a sensitivity analysis bracketing the 1.6–4.0 year range for PFOA and 3.4–5.7 year range for PFOS.
• Document any pregnancies, lactation, or significant kidney-function changes during the exposure window — these now meaningfully affect the back-calculation.
• Where serum data is unavailable, rely on geographic dose reconstruction (location, employment, water-utility records) and explain the fallback.

5. GAPS IN CURRENT PLAINTIFF FILINGS — DEFENSE WILL EXPLOIT

This section identifies recurring weaknesses we have observed in firm-by-firm filings and master complaints. None are fatal; all are fixable; each is a likely Daubert or summary-judgment vulnerability.

5.1 Inconsistent exposure reconstruction

Different plaintiff firms use different dose-reconstruction methodologies. Some use serum-biomonitoring back-calculation; others use geographic exposure estimates; some rely on "occupational exposure proxy" without quantification. The MDL has not yet established a uniform expert methodology, and CMO-26 series have not constrained this. Defendants will pick the weakest plaintiff cases and use them to set Daubert precedent.

Fix: Coordinate within MDL leadership on a uniform exposure-reconstruction protocol covering: serum measurement reliability, half-life selection, sex/age stratification, geographic-cohort dose modeling, occupational exposure metrics, and residual-uncertainty bounds. The C-8 Science Panel's exposure model (PFOA water concentrations × residence/employment × time) is a defensible template, modified for AFFF chemistry.

5.2 Differential diagnosis under-development

Specific causation in kidney cancer cases requires differential diagnosis. Many plaintiff filings recite "elevated PFAS exposure" and "kidney cancer" without addressing the major non-PFAS contributors: tobacco use (smoking confers a roughly 1.5–2× kidney cancer risk), obesity (BMI > 30 confers approximately 1.5× risk), hypertension, occupational solvent exposure (TCE, perchloroethylene), and family history. Defense experts will systematically point to these in cross-examination.

Fix: Each plaintiff intake should include a structured differential-diagnosis worksheet, completed by the treating-physician or retained occupational physician, that addresses each major risk factor and explains why PFAS is more likely than not the substantial contributing factor. The differential should cite literature relative risks for each factor and integrate them into an overall causation analysis.

5.3 Mixed-source exposures

In many cases the AFFF exposure is one of several PFAS sources: contaminated drinking water, fluorochemical occupational exposure, fluorinated food packaging, treated textiles. Defendants will argue that the AFFF contribution is "a small share of total body burden" and that any specific PFAS-attributed disease cannot be specifically attributed to AFFF.

Fix: Where serum biomonitoring shows elevated PFHxS or branched-PFOS isomers (Sm-PFOS), this is signature of AFFF exposure rather than dietary or general-environmental exposure. Trowbridge et al. (2023) documents this pattern in firefighter cohorts. This is a largely overlooked plaintiff strength: PFHxS-elevated and Sm-PFOS-elevated profiles are more strongly attributable to AFFF than to general environmental exposure. Plaintiff experts should foreground this.

5.4 Statute of limitations and discovery-rule briefing

Discovery-rule arguments are not uniformly briefed across firms. Some master complaints invoke discovery without anchoring to a specific accrual event; others rely on continuing-exposure theory without serum-concentration support; some treat 2017 (DuPont/Chemours C-8 settlement) as the operative public-notice date, while a stronger argument anchors to the IARC Group 1 announcement (November 2023) or EPA NPDWR (April 2024).

Fix: Develop a uniform discovery-rule brief and accompanying state-by-state matrix. Anchor public-notice analysis to the IARC Group 1 announcement (Lancet Oncology summary, 30 November 2023), the full IARC Monograph Vol. 135 (February 2025), or the EPA NPDWR (April 10, 2024 announcement; April 26, 2024 Federal Register publication, 89 Fed. Reg. 32,532). For plaintiffs diagnosed before these dates, this is the strongest discovery-rule anchor available.

5.5 Damages models that assume probabilistic survival

Several economic-damages models in firm filings assume "average kidney cancer survival" and "average testicular cancer survival" using SEER aggregate statistics. Defendants will challenge those as ignoring stage-specific survival, treatment success in the individual case, and demographic variation. Where the plaintiff has a particularly favorable individual prognosis (early-stage, favorable histology, complete resection), defendants will argue economic damages are overstated.

Fix: Replace aggregate survival models with stage-specific, treatment-specific, and demographic-specific models. The economic-damages brief should be patient-specific, not population-aggregate.

6. REGULATORY TIMELINE — A PLAINTIFF REFERENCE GUIDE

6.1 EPA actions

• Drinking-water health advisories. EPA's lifetime health advisories for PFOA and PFOS were initially issued at 70 ppt combined (2016) and revised dramatically downward to 0.004 ppt (PFOA) and 0.02 ppt (PFOS) interim health advisories in June 2022. The interim advisories are below the limit of detection of routine analytical methods, signaling that no level of exposure is considered safe.
• National Primary Drinking Water Regulation. Final rule announced April 10, 2024; published in 89 Fed. Reg. 32,532 (April 26, 2024); effective date June 25, 2024. Enforceable MCLs of 4.0 ng/L for PFOA and PFOS, 10 ng/L for PFHxS, PFNA, and HFPO-DA, and a Hazard Index of 1 for any mixture containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS. MCLGs of zero for PFOA and PFOS. Public water systems must complete initial monitoring by 2027 and implement compliance treatment by 2029. (The April 2025 announcement that EPA would "keep" MCLs for PFOA and PFOS — but reconsider others — is a separate development; verify current rulemaking status before any regulatory-anchor argument in court.)
• CERCLA designation. EPA finalized the CERCLA hazardous-substance designation for PFOA and PFOS on April 17, 2024 (Federal Register publication May 8, 2024, 89 Fed. Reg. 39,124; effective July 8, 2024), opening Superfund cost-recovery liability for sites contaminated by these substances.
• Toxic Release Inventory. PFAS reporting under the Toxics Release Inventory was made mandatory in 2020 (NDAA) and expanded in subsequent rulemakings.

6.2 State action

Forty-plus states have adopted PFAS legislation in some form. Of particular relevance for AFFF litigation:

• Washington (Chapter 70A.400 RCW) — bans discharge or use of class B firefighting foam containing intentionally added PFAS for training (RCW 70A.400.010, effective July 1, 2018), and restricts manufacture, sale, and distribution (RCW 70A.400.020). Emergency use during real fires remains permitted.
• New York — Use of PFAS-containing AFFF by fire departments prohibited effective January 1, 2025, with FAA-required-airport carve-out.
• Maine — Banned the manufacture and sale of AFFF (Class B firefighting foam with intentionally added PFAS) effective 2022, except for federally required users (airports, defense contractors); training use prohibited; emergency use during qualifying fires remains permitted pending availability of qualified non-PFAS replacements. Maine's broader 2040 PFAS phase-out applies to consumer products including HVAC refrigerants/foams/aerosol propellants — not firefighting foam, which is governed by the separate AFFF statute.
• California, Colorado, Connecticut, Massachusetts, Minnesota, New Hampshire, Vermont, Wisconsin — restrictions ranging from manufacture/sale prohibitions to take-back programs to landfill disposal restrictions.

A current state-by-state matrix is maintained by the Bryan Cave Leighton Paisner state-by-state report, updated through November 2025 (BCLP, 2025).

6.3 DoD action

The National Defense Authorization Act for Fiscal Year 2020 (Pub. L. No. 116-92) directed DoD to discontinue use of AFFF at DoD installations. Purchase prohibition took effect October 1, 2023; the original use-prohibition deadline of October 1, 2024 was extended to October 1, 2025, then again to October 1, 2026 under the two statutorily authorized one-year waivers. A shipboard-use exemption remains. DoD has approved fluorine-free foam (F3) formulations under MIL-PRF-32725 (DoD, 2023). Estimated transition cost: approximately $2.1 billion (GAO, 2024, GAO-24-107322). The transition has not been smooth — the GAO has documented infrastructure-cleanup, equipment-flushing, and supply-chain bottlenecks. DoD has reported that transition activities have begun across the majority of mobile assets and a substantial share of installations, though precise completion percentages vary by reporting cycle; current transition status should be confirmed against the most recent DoD AFFF Transition quarterly update before any litigation reliance.

DoD's PFAS remediation program for installation cleanup is administered separately under CERCLA-equivalent processes. The regulatory architecture overlaps with private MDL liability, particularly where Federal Tort Claims Act limits private-party recovery against the United States.

6.4 IARC, NTP, and ATSDR

• IARC Monograph Volume 135 (Working Group 2023; Monograph published February 2025) — PFOA = Group 1; PFOS = Group 2B.
• NTP (National Toxicology Program) — concluded that PFOA and PFOS are "presumed to be immune hazards to humans" (NTP, 2016).
• ATSDR (Agency for Toxic Substances and Disease Registry) — Toxicological Profile for Perfluoroalkyls (final, May 2021). Establishes intermediate-duration and chronic-duration MRLs for PFOA, PFOS, PFHxS, and PFNA. Useful as a regulatory-standard anchor for general causation (ATSDR, 2021).

7. DEFENSE EXPERT ARGUMENTS AND HOW TO COUNTER THEM

The defense has refined its expert positioning in the past two years. A summary of the principal defense arguments and the documented plaintiff response:

7.1 "Newer studies do not reproduce the C-8 Science Panel findings."

This is the Boston et al. (2025) argument. Plaintiff response:

• Read the disclosures. Boston et al. authors are paid defense consultants; manuscript preparation was partly funded by Mintz Levin (a defense-side law firm) and the lead author is a retained defense expert. This does not invalidate the analysis — but it goes to weight, not just admissibility, and the jury is entitled to know.
• The IARC Working Group reviewed the same literature Boston et al. cite — and reached the opposite conclusion (Group 1 for PFOA). IARC working groups are independent of both plaintiffs and defendants. When two reviews of the same literature reach opposite conclusions, the independence of the reviewer is dispositive.
• The negative cohort studies often involve lower-exposure populations. The PFAS-cancer dose-response is not monotonically linear at low doses; many cancer-causing exposures show plateau or saturation behavior. The AFFF-firefighter and high-water-contamination cohorts sit in the high-exposure tail where the C-8 Panel findings remain best supported.
• Pooled and meta-analytic estimates that include high-exposure quartile findings retain elevated risk estimates. Steenland et al. (2022) and Stratakis et al. (2023) are the relevant counter-citations.

7.2 "The mechanism of PFOA-induced rodent tumors is PPARα-mediated and not relevant to humans."

This is the longstanding defense mechanistic argument, dating back to the C-8 Panel's deliberations. It has lost ground in the post-IARC era. Plaintiff response:

• IARC's 2023 working group considered and rejected the PPARα-only argument in classifying PFOA as Group 1. The working group cited multiple non-PPARα mechanisms (immunosuppression, oxidative stress, epigenetic change, modulation of estrogen and androgen receptor signaling) that operate in human cells.
• The kidney-resorption mechanism — saturable renal proximal-tubule transport leading to long human kidney exposure — is independent of PPARα. (Olsen et al., 2007; ATSDR, 2021.)

7.3 "Plaintiffs cannot prove specific causation."

The strongest defense argument and the hardest plaintiff lift. Plaintiff response:

• Robust differential diagnosis with documented elimination of major risk factors.
• Serum-biomonitoring profile demonstrating AFFF-signature exposure (elevated PFHxS, branched PFOS isomers).
• Patient-specific dose reconstruction with sex- and age-stratified half-lives.
• Dose-response anchoring to peer-reviewed quantitative risk assessments (Steenland et al., 2022).
• Application of the substantial-factor test rather than a sole-cause test (varying jurisdiction by jurisdiction).

7.4 "Other PFAS sources confound the AFFF attribution."

Plaintiff response:

• PFHxS and branched-PFOS isomers are AFFF-signature in firefighter cohorts and have been documented in the peer-reviewed literature.
• Geographic-cohort exposure: where the plaintiff lives near a known AFFF release site, geographic exposure modeling provides corroborative evidence beyond serum-biomonitoring.
• Occupational documentation: training records, deployment logs, equipment-maintenance assignment records can document AFFF exposure even where dietary/general-population exposure is also present.

7.5 "Statute of limitations bars the claim."

Plaintiff response (state-dependent):

• Discovery-rule anchor at the IARC Group 1 announcement (November 2023) or EPA NPDWR (April 2024).
• Continuing-exposure theory where a plaintiff continues to consume contaminated water or use contaminated gear.
• Occupational-disease presumption statutes in firefighter cases.
• Equitable-tolling arguments where defendants have engaged in active concealment (3M and DuPont internal documents from the 1980s–2000s remain a vein of useful material; many already in the public record from the C-8 settlement.)

8. LITIGATION STATUS — MDL 2873 AT A GLANCE

• Court: D.S.C. (Charleston Division)
• Judge: Hon. Richard M. Gergel
• Master docket: 2:18-mn-2873-RMG
• Active personal-injury cases (approximate, January 2026): ~15,200 active filings on the personal-injury side, with a documented late-September 2025 filing surge that prompted CMO 35 (August 15, 2025) to vacate the October 2025 bellwether and pause intake for documentation verification. Confirm current case count against the SCD MDL portal before relying on this snapshot.
• Disease categories under CMO-33: kidney cancer, testicular cancer, liver cancer, thyroid cancer, thyroid disease, ulcerative colitis.
• Bellwether status: First personal-injury bellwether (kidney cancer) was set for October 20, 2025; vacated under CMO 35. Discovery and bellwether selection ongoing for liver and thyroid cancer claims (Group B). New trial calendar expected to be reset in 2026.
• Science Day: Held June 20, 2025 covering liver and thyroid cancer; up to four experts per side.
• Settlement architecture: Public-water-system tier resolved through 3M ($10.3 billion; preliminary approval August 2023, final approval March 29, 2024 in D.S.C.) and Chemours/DuPont/Corteva ($1.185 billion; agreement announced June 2023, final approval February 2024). Personal-injury tier remains unresolved as of this writing; bellwether outcomes will likely shape any global personal-injury framework.
• State-court parallel docketing: Parallel personal-injury claims pending in multiple state courts; some venues have proceeded faster than the MDL.

9. IMPLICATIONS FOR CASE STRATEGY

1. Refine specific-causation infrastructure now. The bellwether postponement gives plaintiff teams a window to standardize differential-diagnosis worksheets, exposure-reconstruction methodologies, and damages models. The cases that survive will be those with the strongest individual records.
2. Use IARC (November 2023 announcement / February 2025 full Monograph) and EPA 2024 as discovery-rule anchors in older diagnoses. Both are documentary, both are publicly accessible, both are hard for defendants to dispute.
3. Build sex- and age-stratified dose reconstructions. Defendants are sharpening their attacks on Olsen-2007-only methodology. Batzella et al. (2024) and Bartell et al. (2025) are the methodological updates.
4. Prepare cross of Boston et al. (2025) and the broader Roux defense-consultant infrastructure. The disclosure language is already in the published manuscript; this is straightforward Rule 26 and Rule 702 territory.
5. Foreground PFHxS and branched-PFOS biomarkers as AFFF-specific exposure signatures, particularly in firefighter cohorts where multiple PFAS sources may be present.
6. Coordinate with state-court counsel where parallel filings exist. State-court bellwethers may resolve before MDL bellwethers and may set verdict precedent.
7. Track DoD remediation and CERCLA cost-recovery actions for cross-claim leverage where federal entities or contractors are involved.

REFERENCES

1. ATSDR (2021). Toxicological Profile for Perfluoroalkyls. U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. May 2021. https://www.atsdr.cdc.gov/toxguides/toxguide-200.pdf
2. Bartell SM, et al. (2025). "Perfluorooctanoic acid serum concentrations and half-lives in a community exposed to contaminated drinking water in New York State." Journal of Exposure Science & Environmental Epidemiology. https://www.nature.com/articles/s41370-025-00769-z (Hoosick Falls / Petersburgh, NY cohort.)
3. Batzella E, Rosato I, Pitter G, Da Re F, Russo F, Canova C, Fletcher T (2024). "Determinants of PFOA Serum Half-Life after End of Exposure: A Longitudinal Study on Highly Exposed Subjects in the Veneto Region." Environmental Health Perspectives 132(2):27007. PubMed: 38306197. PMC10836585.
4. BCLP (2025). "PFAS in Firefighting Foam (AFFF) and Equipment: State-by-State Regulations." Bryan Cave Leighton Paisner LLP, updated November 2025. https://www.bclplaw.com/en-US/events-insights-news/pfas-in-firefighting-foam-afff-and-equipment-state-by-state-regulations.html
5. Boston C, Keck S, Naperala A, Collins J (2025). "The evolution of PFAS epidemiology: new scientific developments call into question alleged 'probable links' between PFOA and kidney cancer and thyroid disease." Frontiers in Public Health 13:1532277, published April 9, 2025. https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2025.1532277/full. All authors employed by Roux; lead author retained as defense expert in PFAS litigation; manuscript preparation partly funded by Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
6. C-8 Science Panel (2011–2012). Probable-link evaluations. Leach v. DuPont, Wood Cir. Ct., W. Va., Civ. Action No. 01-C-608. Reports archived at http://www.c8sciencepanel.org.
7. DoD (2023). "MIL-PRF-32725 — Fluorine-Free Foam Performance Specification." U.S. Department of Defense. http://www.acq.osd.mil/eie/eer/ecc/pfas/.
8. EPA (2024a). "PFAS National Primary Drinking Water Regulation; Final Rule." 89 Fed. Reg. 32,532 (April 26, 2024); announced April 10, 2024; effective June 25, 2024. https://www.federalregister.gov/documents/2024/04/26/2024-07773/pfas-national-primary-drinking-water-regulation.
9. EPA (2024b). "Designation of Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) as CERCLA Hazardous Substances." Final Rule signed April 17, 2024; published 89 Fed. Reg. 39,124 (May 8, 2024); effective July 8, 2024. https://www.federalregister.gov/documents/2024/05/08/2024-08547/designation-of-perfluorooctanoic-acid-pfoa-and-perfluorooctanesulfonic-acid-pfos-as-cercla-hazardous
10. EPA (2025). "EPA Announces It Will Keep Maximum Contaminant Levels for PFOA, PFOS." Press release. https://www.epa.gov/newsreleases/epa-announces-it-will-keep-maximum-contaminant-levels-pfoa-pfos. Verify current rulemaking status before relying on regulatory anchor.
11. GAO (2024). "Firefighting Foam: DOD is Working to Address Challenges to Transitioning to PFAS-Free Alternatives." GAO-24-107322. https://www.gao.gov/products/gao-24-107322.
12. IARC (2025). "Carcinogenicity of perfluorooctanoic acid and perfluorooctanesulfonic acid." IARC Monographs on the Identification of Carcinogenic Hazards to Humans, Volume 135. International Agency for Research on Cancer, Lyon, France. Working Group meeting: November 7–14, 2023. Full Monograph published February 2025. Summary findings published The Lancet Oncology 24(12):1352–1353 (online 30 November 2023). https://monographs.iarc.who.int/iarc-monographs-volume-135/.
13. ITRC (2023). "Per- and Polyfluoroalkyl Substances (PFAS) Technical Resources." Interstate Technology and Regulatory Council. https://pfas-1.itrcweb.org.
14. Mastrantonio M, et al. (2024). "All-cause, cardiovascular disease and cancer mortality in the population of a large Italian area contaminated by perfluoroalkyl and polyfluoroalkyl substances (1980–2018)." Environmental Health 23:43. https://ehjournal.biomedcentral.com/articles/10.1186/s12940-024-01074-2.
15. NCI (2025). "PFAS Exposure and Risk of Cancer." Division of Cancer Epidemiology and Genetics. https://dceg.cancer.gov/research/what-we-study/pfas.
16. NTP (2016). "NTP Monograph on Immunotoxicity Associated with Exposure to Perfluorooctanoic Acid (PFOA) or Perfluorooctane Sulfonate (PFOS)." National Toxicology Program. https://ntp.niehs.nih.gov.
17. Olsen GW, et al. (2007). "Half-Life of Serum Elimination of Perfluorooctanesulfonate, Perfluorohexanesulfonate, and Perfluorooctanoate in Retired Fluorochemical Production Workers." Environmental Health Perspectives 115(9):1298–1305. https://pmc.ncbi.nlm.nih.gov/articles/PMC1964923/. n = 26 retired workers (24 male, 2 female); geometric-mean half-lives PFOS 4.8y (95% CI 4.0–5.8), PFHxS 7.3y (5.8–9.2), PFOA 3.5y (3.0–4.1).
18. Seyyedsalehi MS, Boffetta P (2023). Meta-analysis of PFAS exposure and kidney cancer. PFOA-specific meta-RR 1.23 (95% CI 0.99–1.51); broader any-PFAS meta-RR 1.18 (95% CI 1.05–1.32, 11 studies).
19. Steenland K, Woskie S (2012). "Cohort mortality study of workers exposed to perfluorooctanoic acid." American Journal of Epidemiology 176(10):909–917. PMID 23079607. SMR for kidney cancer in highest cumulative-exposure quartile (lagged analysis) = 3.67 (95% CI 1.48–7.57; n = 11 deaths).
20. Steenland K, et al. (2022). "Risk assessment for PFOA and kidney cancer based on a pooled analysis of two studies." Environment International. https://www.sciencedirect.com/science/article/pii/S016041202200352X. PMC9378494.
21. Stratakis N, et al. (2023). "Per- and Poly-fluoroalkyl Substances (PFAS) Exposure and Risk of Kidney, Liver, and Testicular Cancers: A Systematic Review and Meta-Analysis." La Medicina del Lavoro (PMC10627102).
22. Trowbridge J, et al. (2020, 2023). Firefighter PFAS biomonitoring studies — California women firefighters; four municipal departments. PMC9859935.
23. U.S. Department of Defense (2020). National Defense Authorization Act for Fiscal Year 2020, Pub. L. No. 116-92. AFFF transition mandate.
24. Vieira VM, et al. (2013). "Perfluorooctanoic Acid (PFOA) Exposures and Incident Cancers among Adults Living Near a Chemical Plant." Environmental Health Perspectives 121(11–12):1313–1318. https://ehp.niehs.nih.gov/doi/10.1289/ehp.1306615. Adjusted odds ratios for kidney cancer were 2.0 in the high (95% CI 1.3–3.2; statistically significant) and 2.0 in the very high (95% CI 1.0–3.9; borderline) modeled-serum-PFOA exposure categories.

This memorandum is prepared as background research and does not constitute legal advice. All citations have been verified to the publicly accessible URLs as of the date of this memorandum. Recipients should independently verify current status of any rulemaking, MDL order, or peer-reviewed publication before relying on this material in court. Where the manuscript identifies a specific snapshot value (case counts, settlement amounts, regulatory deadlines), the snapshot date is identified inline; counts and deadlines drift, and the reader should confirm current status before citing.