Toxic Tort Litigation Expert Testimony Admissibility: Significant Georgia Appellate Ruling

In a recent decision that could alter how plaintiffs present expert witness testimony in state court toxic tort claims, the Georgia Court of Appeals in Sterigenics US LLC v. Mutz, No. A25A1377, 2025 WL 3041770 (Ga. Ct. App. Oct. 31, 2025), addresses a core issue in toxic tort litigation: the standards governing admissibility of expert witness testimony about general causation.

Plaintiffs in this consolidated set of cases claimed that exposure to ethylene oxide (EtO), emitted by a Sterigenics sterilization facility in Cobb County, Georgia, caused cancer or birth defects to themselves or their children. These eight bellwether cases were selected for discovery and pretrial motions, with the key issue focusing on whether plaintiffs' expert testimony regarding general causation satisfied Georgia Rule 702, which tracks Federal Rule of Evidence 702.

Under Rule 702, toxic tort plaintiffs must demonstrate both general causation (i.e., the chemical's capacity to cause the kind of harm alleged) and specific causation (i.e., linking exposure to the chemical to the plaintiff's illness or disease). The controlling framework, drawn from Eleventh Circuit precedent (notably McClain v. Metabolife Intl., Inc., 401 F.3d 1233 (11th Cir. 2005)), splits toxic tort cases into two categories. In the first, the medical community broadly recognizes the substance as causing the harm (e.g., asbestos causing mesothelioma, cigarette smoke causing cancer). In the second category, in the absence of a strong consensus concerning causation, plaintiffs must present expert testimony that reliably explains why and at what dose the substance causes harm. This typically means offering dose-response analysis or valid epidemiological studies.

In Sterigenics, plaintiffs presented expert testimony asserting that EtO exposure elevates cancer risk, with some experts contending that "any exposure" above natural background levels could be harmful. Dr. Leslie Stayner stated that, in his expert opinion, strong evidence exists that links EtO exposure to elevated risk of lymphatic, hematopoietic, and breast cancers. Dr. Dean Felsher provided a similar opinion as to the link between EtO exposure and increased risk of lymphatic, hematopoietic, and breast cancers; however, Dr. Felsher testified that "any level above background" can contribute to a cancer diagnosis. And Dr. Aliasger Salem opined that EtO exposure can cause hematopoietic and breast cancers and birth defects, with "exposure above background" increasing those risks.

The trial court applied McClain, allowing one expert's testimony (Dr. Stayner), excluded the others, and granted summary judgment to Sterigenics on birth defect claims after finding that the remaining evidence did not reliably link EtO to the alleged harms. The court concluded that EtO did not fit neatly into either toxic tort category and held that, in these instances, expert testimony on general causation need not include a specific dose-response threshold. It acknowledged that EtO is generally recognized as a carcinogen but was hesitant to place it in the first category of toxic tort cases. Using this approach, the trial court permitted Dr. Stayner's opinion that any exposure to EtO can cause cancer but excluded similar testimony from Dr. Felsher and Dr. Salem regarding exposures above background levels. Additionally, the court found that Dr. Felsher and Dr. Salem did not provide reliable opinions linking EtO to birth defects, so their testimony on that subject was also excluded.

However, in finding an abuse of discretion, the Court of Appeals held that the trial court misapplied the McClain standard, particularly by allowing an "any exposure" theory to suffice without a rigorous reliability analysis when EtO was not universally accepted as causative for the plaintiffs' cancers and birth defects. Specifically, the appellate court held that the Eleventh Circuit does not allow an exception to its two-tier classification for toxic tort cases and that, under McClain, experts must identify a harmful level of exposure that could cause the alleged harm when using the dose-response methodology to show general causation. The appellate court vacated and remanded the trial court's order, instructing it first to determine whether EtO falls into the category of widely recognized substances, and, if not, to carefully scrutinize the reliability of the expert methodologies under Rule 702.

The Sterigenics decision sets a clear precedent for future toxic tort litigation in Georgia: plaintiffs must move beyond broad assertions or "any exposure" theories when the alleged toxin and health effect lack universal acceptance in the scientific community. Instead, courts will require evidence from experts that explains the dose-response relationship or establishes causation through sound epidemiological or background risk data. As such, this ruling may make it more difficult for plaintiffs to advance toxic tort claims involving chemicals where scientific consensus is unsettled, underscoring the need for thoroughly substantiated expert testimony moving forward. The decision also provides strong support for an appeal of a trial court decision on the admissibility of expert witness testimony that falls outside the boundaries of McClain and Rule 702.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.