The Causation Gap

To bridge the scientific gap between trace chemical exposure and human disease, plaintiff attorneys must overcome two massive evidentiary obstacles—proving the exact level of an individual’s PFAS exposure and verifying that this specific exposure directly caused their disease.

This lack of a uniform legal baseline for exposure stems directly from how people come into contact with the “forever chemicals.”

“The general public’s day-to-day contact with everyday retail goods involves minuscule, trace exposure levels completely distinct from the heavy, high-dosage occupational exposure experienced by chemical factory workers or military firefighters,” says George Buermann, a partner at Goldberg Segalla and vice chair of the law firm’s environmental practice group. “Such health conditions are common and have many alternative causes, allowing corporate defendants to easily argue that a plaintiff’s illness had nothing to do with PFAS.”

Defense teams have historically used this wide variance in human exposure to block mass litigation from moving forward as unified class actions. As Dan Bailey, chair at law firm Bailey Cavalieri, points out, “Defendants are successfully blocking certification by demonstrating that every consumer has a completely different history of exposure, varied lengths of chemical contact, and exposure to entirely different finished products.”

From an insurance underwriting perspective, preventing certified class actions significantly protects the commercial liability market. Without a shared exposure baseline, large-scale plaintiff group efforts quickly fall apart, observes Robert Hartwig, clinical associate professor of finance at the University of South Carolina.

“When plaintiffs attempt to form a class, corporate defense attorneys can successfully demonstrate that the individuals do not share a common legal baseline and that there is no scientifically verifiable way to establish a direct causal link between an individual’s specific disease and a potential PFAS exposure,” Hartwig says, noting that the legal strategy forces plaintiff attorneys into costly, individualized litigation for every claimant.

Rather than walking away from these strict evidentiary hurdles, the plaintiff bar is adapting. Firms are pooling deep financial resources to fund proprietary, long-term epidemiological cohort studies designed to map their own precise dose-response curves and link low-level consumer exposure to specific bodily diagnoses. Concurrently, lawyers are shifting focus away from cases involving isolated injuries toward regional aquifer contamination, which provides a direct path to securing massive infrastructure settlements. The fees generated from those early infrastructure victories now provide the capital needed to finance the costly medical science required to overcome the defense’s class-action barriers.