Fourth Circuit Revives Ethylene Oxide Medical Monitoring Suit, Expanding Article III Standing for Environmental Exposure Claims

Standing

The class action suit was brought against Union Carbide Corporation and Covestro LLC alleging that class members were exposed to EtO emitted from a facility owned by the defendants in South Charleston, West Virginia. The claim is based on a medical monitoring cause of action recognized under West Virginia state law.² After the suit was removed to federal court, it was dismissed by the District Court for the Southern District of West Virginia for lack of Article III standing.³ The district court characterized Somerville’s alleged harm as merely an “increased risk of eventually getting cancer.”⁴ Applying the Supreme Court’s decision in TransUnion, LLC v. Ramirez, plaintiffs seeking prospective, injunctive relief may ground their claims in a risk of future harm, but those suing for damages must present a concrete, present injury.⁵ Here, the district court could not recognize Sommerville’s increased risk as an imminent, concrete injury sufficient for Article III standing for a damages claim in federal court.

The Fourth Circuit criticized the district court’s framing of the plaintiff’s injury as a mere risk of future harm, recharacterizing it as two related, present-day injuries. “Sommerville’s alleged injury is not an ‘increased risk of cancer development due to the alleged EtO emissions.’ Sommerville’s injury is her ‘exposure itself’ to ‘environmental toxins’ . . . and ‘the concomitant need [to pay] for medical testing’ today to mitigate an increased risk of illness which Sommerville would not bear but for the Plant Owners’ actions.”⁶ According to the majority, that injury is “concrete and ripe,” because the exposure has led a qualified physician to conclude that Sommerville “must . . . pay for and undergo periodic diagnostic medical examination now.”⁷ The court grounded the diagnostic cost injury in the “traditional common-law principle of avoiding physical injury” recognized in asbestos exposure cases.⁸ As for TransUnion, the majority considered Sommerville less analogous to class members in that case that were merely exposed to risk of harm, and more similar to those who had standing because their credit reports had actually been provided to third parties and thereby had suffered concrete, reputational harm. Like these plaintiffs, Sommerville had been actually exposed to EtO, and that exposure led to the concrete, present harm of diagnostic costs.⁹

In a dissenting opinion, Chief Judge Diaz rejected the majority’s characterization of Sommerville’s injury and the standing ruling as contrary to Fourth Circuit precedent. In Judge Diaz’s view, Sommerville’s injury is not the EtO exposure itself, but only the medical monitoring costs resulting from exposure. The dissent points not just to TransUnion, but to the Fourth Circuit’s own precedent in a credit monitoring case, Beck v. McDonald, which held that, “for costs stemming from a potential future harm to be an injury in fact, the underlying future harm must be a non-speculative one.”¹⁰ Judge Diaz draws a direct line between the Beck holding, where an injury of credit monitoring costs and underlying risk of identity theft were too speculative for standing, and Sommerville’s medical monitoring costs and underlying risk of developing cancer. “In each case, plaintiffs seek to ‘monitor’ something that may occur, not the event that’s already occurred.”¹¹ In response, the majority distinguished Beck by emphasizing that the exposure itself is an injury that exists already—and that Sommerville is not suing based on her speculative threat of developing cancer, but on her “current need for specific medical services.”¹²

Sommerville’s more expansive reading of Article III standing brings the Fourth Circuit closer in line with the minority of states¹³ that recognize a plaintiff’s right to sue based on no-injury medical monitoring claims. Holding that an exposure that “render[s] monitoring a present medical necessity” is sufficient, the court recognizes Article III standing where there is “a significantly increased risk of contracting a particular disease.”¹⁴

Daubert

The Fourth Circuit also reversed the district court’s Daubert ruling to exclude the testimony of the plaintiff’s air modeling expert, Dr. Ranajit Sahu. The district court had excluded the report based on what it saw as serious methodological flaws in the validity of the underlying data and Dr. Sahu’s application of that data to develop his conclusions.¹⁵ The district court rejected Dr. Sahu’s sourcing of emissions data from a group of facilities, that included the South Charleston facility at issue, because the report did not disaggregate the impacts of emissions from each facility.¹⁶ The model also used historical data, which the district court characterized as unreliable, and made an unsupported assumption that operations at the facilities had been historically unchanged.¹⁷ The district court also rejected Dr. Sahu’s failure to validate data from a 1984 state emissions inventory that had been repeatedly protested by defendants as inaccurate, his reliance on “worst case emissions rates” rather than actual production rates from 1985 to 1989, and his use of emissions rates reported for regulatory purposes from 1990 to 2019.¹⁸ In addition to issues with Dr. Sahu’s sourcing and application of emissions data, the district court criticized the use of meteorological data sourced from three different locations and the use of background EtO levels from EPA’s nationwide National Air Toxics Assessment (“NATA”) database instead of relevant local sources or sampling.¹⁹

Despite the deferential standard of review applicable to Daubert determinations, the Fourth Circuit exhibited little deference in reversing the lower court’s ruling. The majority repeatedly emphasized the principle that questions regarding the factual underpinnings of an expert’s opinions are questions of credibility (for the fact finder’s consideration), not questions of admissibility.²⁰ In the majority’s view, the district court had impermissibly inserted itself into a battle of experts, ignoring Dr. Sahu’s reasoning for his choice of modeling parameters in favor of defendants’ expert’s reasoning. This included the district court’s conclusion on the reliability of emissions numbers reported for regulatory purposes, its unnecessary scientific judgments regarding the use of meteorological data from multiple locations, and its imposition of a requirement to “validate” data.²¹

Judge Diaz again took the district court’s side, criticizing the majority’s outlook as giving a green light to Dr. Sahu’s modeling results based solely on the reliability of the underlying model —as distinct from its inputs— and allowing all questions of data reliability to go to the fact finder rather than to factor into admissibility. “[A]n expert who constructs a model based on faulty assumptions and irrelevant data shouldn’t be handed a ‘get-out-of-Daubert-free card’ simply because he uses an otherwise reliable modeling system.”²² To Judge Diaz, the reliability of a modeling methodology doesn’t end with selecting a modeling system—the expert must also develop inputs and assumptions to create the model. And Daubert instructs that those inputs must be supported by “scientifically valid reasoning or methodology” and based on “sufficient facts or data.”²³ Judge Diaz further criticized the majority for overreading the district court’s requirement that Dr. Sahu “substantiate” or “support” his data and mischaracterizing the lower court as imposing a data quality validation protocol.²⁴ Despite the majority’s invocation of Bresler regarding questions of weight and credibility versus admissibility, district courts must have the authority to decide that an expert’s opinion lacks sufficient support in the record or conclude that there is “too great an analytical gap” between an expert’s data and conclusion.²⁵

Implications

The implications of this decision are likely far greater than apparent from the text of the majority opinion. If the plaintiff prevails on her claim that a one-in-a-million incremental cancer risk for a lifetime of exposure²⁶ is sufficient legal injury to provide standing, EPA risk assessments, for example, those at numerous Superfund sites, would provide plaintiffs with straightforward support for future medical monitoring claims. Even the most trivial exposures could create standing for medical monitoring cases, risks that the district court describes as “a statistical anomaly, not ‘significant.’”²⁷ Transforming a conservative regulatory threshold into a demonstration of legal injury in this manner represents a substantial broadening of traditional tort concepts.

Similarly, the Sommerville majority shifts the Daubert standard in the Fourth Circuit to strongly favor admission for air modeling experts, again in ways that are likely more significant than the face of the opinion initially suggests. The district court had fundamental problems with the foundation of the plaintiff’s expert’s opinion, principally based on his use of assumptions to fill data gaps for periods when historic air emissions were not available. The majority opinion put little weight on the district court’s gatekeeping function for such issues, instead characterizing the court as improperly taking a side on an issue that properly went to the weight of the evidence, not its admissibility. Ultimately, however, the majority opinion did not really engage with the district court’s fundamental point, that the expert’s use of assumptions to fill data gaps rested on an unsupported ipse dixit (“because I said so”). Because lack of historic data is often a problem for retrospective air modeling exercises, if the majority’s opinion is read to suggest that a district court cannot exclude testimony based on assumptions used to fill data gap in cases where such assumptions are not sufficiently supported—and the plaintiffs’ bar will certainly cite it for this proposition—such use of air models will go to the jury.

This combination of lenient admissibility of air models and one-in-a-million risks establishing actionable legal injury substantially alters the toxic tort landscape. Facilities located in the Fourth Circuit face increased litigation risk for emission exposure claims, not only for EtO but also for PFAS and other chemical constituents associated with potential long-term carcinogenicity. By deeming diagnostic testing a present injury and restricting the ability of district courts to exclude expert testimony, Sommerville would likely inflate early-stage settlement values and litigation risk generally.

In their petition for rehearing, the defendants focused on the tension between the majority’s evidentiary holding and Federal Rule of Evidence 702. While the majority repeatedly cited a 2017 case, Bresler, for its assertion that issues regarding data sourcing and modeling inputs are questions for the jury, Rule 702 was thereafter amended in 2023 to clarify that questions of the sufficiency of an expert’s basis for his testimony were questions of admissibility, not weight.²⁸ And, the petition asserts, the Fourth Circuit has subsequently applied Rule 702 consistent with this understanding—and contrary to Bresler.²⁹ On the standing issue, the defendants argue that the majority’s ruling creates conflicts with the Beck precedent cited in Judge Diaz’s dissent, in that the majority failed to consider whether the plaintiff’s injuries were “certainly impending.” Further, the defendants argue that the majority opinion evaluates standing based on allegations rather than evidence, despite the summary judgment posture of the case. For these reasons, the defendants seek reconsideration and reversal of the majority opinion in its entirety.

The Fourth Circuit has yet to answer the defendants’ request for reconsideration. In the meantime, potentially affected entities are advised to work with counsel to track the developments on these exposure suits and ensure that their legal strategy is acclimated to the current landscape.

¹ Sommerville v. Union Carbide Corp., No. 24-1491, 2025 WL 2383496, at *5 (4th Cir. 2025).

² See Bower v. Westinghouse Elec. Corp., 522 S.E.2d 424 (W. Va. 1999).

³ Sommerville v. Union Carbide Corp., No. 2:19-cv-00878, 2024 WL 2139394 (S.D.W. Va. 2024) (“Sommerville II”).

⁴ Id. at *7.

⁵ TransUnion, LLC v. Ramirez, 594 U.S. 413, 417, 435 (2021).

⁶ Sommerville, 2025 WL 2383496, at *5 (quoting Bower, 522 S.E.2d at 430).

⁷ Id.

⁸ Id. (citing Bourgeois v. A.P. Green Indus., Inc., 716 So. 2d 355 (La. 1998)).

⁹ Id. at *6, citing TransUnion, 594 U.S. at 417.

¹⁰ Id. at *14 (Diaz, J., dissenting) (citing Beck v. McDonald, 848 F.3d 262 (4th Cir. 2017)).

¹¹ Id.

¹² Id. at *7.

¹³ Nine states recognize medical monitoring damages without a showing of present injury: Arizona, California, Florida, Missouri, New Jersey, Ohio, Pennsylvania, Utah, and West Virginia.

¹⁴ Sommerville, 2025 WL 2383496, at *6.

¹⁵ Sommerville v. Union Carbide Corp., 2024 WL 1204094, at *7 (S.D.W. Va. 2024) (“Sommerville I”).

¹⁶ Id. at *9.

¹⁷ Id. at *10-11.

¹⁸ Id. at *12-*14.

¹⁹ Id. at *15, *17.

²⁰ Sommerville, 2025 WL 2383496, at *9 (citing Bresler v. Wilmington Tr. Co., 855 F.3d 178, 195 (4th Cir. 2017)).

²¹ Id. at *10-11.

²² Id. at *16 (Diaz, J., dissenting).

²³ Id. (quoting Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 592-93 (1993); Fed. R. Evid. 702(b)).

²⁴ Id. at *17 (Diaz, J., dissenting).

²⁵ Id. (citing Fed. R. Evid. 702(b); Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997)).

²⁶ EPA generally considers an incremental lifetime cancer risk in the range of 1 in 10,000 (1 × 10⁻⁴) to 1 in 1,000,000 (1 × 10⁻⁶) as acceptable for regulatory purposes. This risk range is used in EPA’s Superfund program and other risk assessment contexts to guide decisions about acceptable levels of exposure to carcinogens. See, e.g., U.S. Env’t Prot. Agency, “Risk Assessment Guidance for Superfund, Volume III Part A: Human Health Evaluation Manual (Part A),” EPA-540-R-02-002, December 2001, Section 7.1, p. 7-1. In another medical monitoring case, the Third Circuit recognized a one-in-a-million risk as significant. See Redland Soccer Club, Inc. v. Dep’t of Army of U.S., 55 F.3d 827, 840 n.7 (3d Cir. 1995).

²⁷ Sommerville II, 2024 WL 2139394 at *9.

²⁸ Motion for Rehearing En Banc at 6, Sommerville v. Union Carbide, 2025 WL 2383496 (4th Cir. 2025) (quoting Fed. R. Evid. 702 advisory committee’s note to 2023 amendment).

²⁹ See Sardis v. Overhead Door Corp., 10 F.4th 268 (4th Cir. 2021).