On August 18, 2025, the United States Court of Appeals for the Fourth Circuit issued its long-awaited decision in Sommerville v. Union Carbide Corp., reversing the U.S. District Court for the Southern District of West Virginia’s summary judgment ruling in favor of the plant owner defendants. In the case, the lead plaintiff, on her own behalf, and others similarly situated, alleged exposure to ethylene oxide (“EtO”). It is claimed that EtO is a cancer-causing gas. The lawsuit involves manufacturing operations in South Charleston, West Virginia, that operated between 1978 and 2019. The plaintiff claims that the plant emitted EtO into the atmosphere, that she breathed the EtO, and her exposure to EtO increased her risk of developing disease. The plaintiff also claims she has a present need to manage her increased risk of illness through medical monitoring and diagnostic testing and is seeking payment of the costs from the plant owners.
The appeal was a challenge to two orders of the federal district court. The first challenged holding involved the lower court’s decision that the plaintiff lacked a “manifest” physical injury and therefore had no Article III standing to sue. The second appealed ruling involved the district court’s exclusion of expert testimony.
In reversing the lower trial court, the Fourth Circuit noted that “the district court’s analysis went off course” in framing the plaintiff’s “injury as an increased risk of ‘eventually getting cancer.’” To the Fourth Circuit, medical monitoring of a plaintiff’s injury – like Sommerville’s injury – is “exposure itself to environmental toxins tortiously emitted by Plant Owners which affect the body in ways that do not become manifest for several years” and the need to pay for medical testing today to mitigate an increased risk of illness, which the plaintiff would not have to pay but for the plant owners’ actions. Since West Virginia common law permits medical monitoring recovery to avoid physical injury, the Fourth Circuit reasoned that Sommerville’s injury is not any less actual, concrete, or serious than a visible injury like a broken arm. Further, the Fourth Circuit’s opinion notes Sommerville’s injury is such that the plant owners exposed her to EtO in such quantities that, based on a qualified medical opinion, she must now pay for and undergo medical monitoring and diagnostic testing.
Having addressed in the plaintiff’s favor the question of Article III standing, the Fourth Circuit’s decision next addressed the issue of whether the district court properly excluded Sommerville’s proposed expert – Dr. Sahu – who modeled EtO emissions using the “AERMOD” dispersion model. In broad summary, the Fourth Circuit additionally reversed the district court’s ruling, noting that its conclusions were abuses of discretion and none of the reasons for which the district court excluded Dr. Sahu’s testimony were proper. The Fourth Circuit held that Sommerville established by a preponderance of the evidence that Dr. Sahu’s testimony is admissible.
We will be following the impact of the Fourth Circuit’s decision particularly as to whether other courts will be persuaded that a plaintiff lacking physical injury qualifies for Article III standing in medical monitoring suits involving environmental exposure claims like EtO.
