Barry Law Environmental and Earth Law Journal

October 27, 2025

Since the 1930’s, chemicals known as PFAS, short for polyfluoroalkyl substances, have made modern life easier. They coat cookware, waterproof fabrics, and strengthen firefighting foams. Yet these “forever chemicals” come with lasting consequences. The name forever comes from the chemical’s properties. Only recently are scientists discovering that the chemicals don’t dissolve naturally but instead build up in water, soil, and even in humans.

Across the country, communities are discovering PFAS contamination in their drinking water and linking it to serious health concerns. The science connecting PFAS exposure to diseases is growing, but far from complete. This uncertainty has created a major problem once the fight enters the courtroom.

PFAS in the Courtroom

In environmental cases, expert witnesses connect the dots between the defendant corporation’s actions and the damages from these forever chemicals. They help juries understand why the chemical doesn’t break down and whether it caused harm. Judges, acting as gatekeepers under Daubert, must decide if those experts are reliable enough to testify. These rules were created favoring fields where science has been long-standing and have decades of repetition. Unfortunately, PFAS science does not always work that way. As a sad consequence to this, experts are being struck, not because they lack the knowledge for an expert, but rather because the expert is basing their opinion on studies that are new and haven’t had their chance to be proven.

Because research on PFAS is still developing, experts rely on probability and population-level studies. Judges applying strict reliability standards often exclude those experts for being too uncertain. As a result, entire communities are denied their chance to present the best science available. The courtroom’s demand for absolute certainty clashes with the nature of emerging environmental research.

When Reliability Blocks Justice

This tension has harmed communities across the nations. In many PFAS cases, the evidence is strong enough to suggest harm but not definitive enough to meet courtroom standards. Plaintiffs are told their science is too uncertain, even though it is the best information that currently exists. Meanwhile, companies that produced or used PFAS continue to benefit from this uncertainty.

The law’s insistence on finality can trap victims because they cannot win without more science, but they cannot get more science without the transparency that lawsuits can provide. In this way, the evidentiary rules in place have been siding with industry interests more than public health.

Connecting Science and the Law

Courts could take several steps to close this gap. First, judges could focus on whether an expert’s reasoning is sound given the current limits of PFAS research, rather than expecting complete certainty. Reliability should reflect the best methods available, not the most conclusive ones.

Second, courts might take judicial notice of basic facts that are no longer in dispute, such as PFAS in the environment. That would let experts concentrate on contested issues like exposure levels, instead of spending time proving that their standards are accurate.

Finally, advisory committees could issue guidance explaining how evidentiary rules apply to probalistic sciences. Clarifying that new methods can still be reliable would give judges confidence to admit credible PFAS testimony without lowering scientific standards.

A Precautionary Perspective

In these cases, environmental harm is happening before the courts have a chance to address it. In these situations, courts could adopt a standard found in international environmental law, the precautionary perspective. This standard holds that if credible evidence suggests a serious public risk, expert testimony should be admitted as long as it meets basic reliability standards. This approach would allow juries to weigh the evidence themselves and decide whether they believe it, rather than silencing the science altogether.

Keeping the Gate to Justice Open

PFAS litigation highlights how the law can struggle to keep pace with science. When judges exclude experts because their fields are still growing, they risk denying communities already suffering from contamination their day in court.

Justice should reflect the world as it is, not over whether the science can be proven. The law must evolve alongside science so that those harmed by forever chemicals have a fair chance to be heard. Waiting for complete certainty means waiting too long for justice.

Written by Brady Clark, Associate Editor 2025-2026