In re Deepwater Horizon Belo Cases, — F.4th –, 2024 WL 4522690 (11th Cir. Oct. 18, 2024), is not a drug or device case. It is the Eleventh Circuit’s review of the Northern District of Florida’s exclusion of the plaintiffs’ general causation experts in a toxic tort exposure case arising from the clean-up of the Deepwater Horizon oil spill. But the issues are identical to Rule 702 issues we face in our cases.
In the years that followed the oil spill, numerous personal injury lawsuits were filed by clean-up workers and local residents alleging conditions such as chronic sinusitis. The cases were consolidated and a settlement was reached in 2012 dividing the claims into two categories. Those diagnosed before the cutoff date could submit a claim for fixed compensation from the settlement pot. Those diagnosed after the cutoff date could file individual tort suits. Thousands of plaintiffs filed “backend” suits, several hundred of which were transferred to the Northern District of Florida. To save time and expense, the court bifurcated the litigation to address general causation first because “the medical community does not widely accept[ ] that oil, dispersants, or any chemicals associated with them can cause common conditions like chronic sinusitis.” Id. at *3.
In a 79-page report and recommendation by the magistrate judge that was adopted by the trial judge, the court excluded plaintiffs’ general causation experts on several grounds chief among them being that neither expert “identified a minimum level of exposure at which crude oil, its dispersants, or the chemicals in them are hazardous to human beings” – a threshold test. Id. at *4. Absent expert evidence establishing general causation, the court went on to grant defendant’s motion for summary judgment.
On appeal the Eleventh Circuit found no abuse of discretion by the trial court’s exclusion of the expert testimony and upheld both that decision and the subsequent entry of summary judgment. The opinion starts by explaining general causation–“whether an agent increases the incidence of disease in a group”—and the types of evidence needed to prove it–epidemiological evidence, dose-response relationship, and background risk of disease. Id. at *1-2. We recommend the court’s “primer” on all three, but for today’s purposes we focus on the dose-response relationship. Because “all substances can potentially be toxic,” neither the scientific community nor Rule 702 accepts a no-threshold exposure level. The “single most important factor” in establishing general causation is evidence of what dose or level of exposure is associated with an increased risk of a specific adverse event. Id. at *2.
Plaintiffs argued that establishing the level at which exposure can cause the harm alleged—the threshold level—was relevant to specific causation only. But that files directly in the face of Eleventh Circuit precedent dating back to McClain v. Metabolife International, Inc., 401 F.3d 1233 (11th Cir. 2005), in which the court ruled that a toxic-tort plaintiff “must demonstrate the levels of exposure” to the alleged toxin “that are hazardous to human beings generally.” Id. at 1241 (emphasis added) (excluding expert who did not opine about the level of exposure at which the ephedrine/caffeine in defendant’s product causes harm). Establishing the “threshold level” is the “basic methodology that scientists use to determine causation,” and therefore critical to admissibility under Rule 702. Therefore,
[t]he district court did not abuse its discretion when it required the experts to identify a “toxin” and prove it “[was] harmful above a particular threshold” and excluded them because they failed to do so. Instead, it applied general-causation principles drawn directly from [11th Circuit] precedents, aligned with those of other circuits.
In re Deepwater Horizon, at *6.
Plaintiffs’ attempt to shift “threshold level” evidence to specific causation confuses the issue. Only after the harmful level is established as to the general population, does the analysis move to whether an individual plaintiff was exposed to that level, i.e. specific causation. In other words,
[a] plaintiff’s exposure to the threshold dose of a toxin is relevant to specific causation. Yet we also ask, under our general-causation framework, whether a harmful level of the toxin exists in the first place.
Id.
While the failure to establish the threshold harmful level was sufficient by itself to exclude plaintiffs’ experts, the Eleventh Circuit found the district court had a myriad of other reasons to support its decision. For example, plaintiffs’ experts failed to identify a statistically significant association in the literature; relied on studies addressing acute rather chronic conditions or different conditions (asthma) altogether; ignored limitations and inconsistencies in the relied on studies; and in their epidemiological analysis failed to adequately address the Bradford Hill factors (one expert only discussed three of the nine factors). Id. at *7. Rather than abusing its discretion, the district court had ample, well-supported reasons for excluding the experts and granting summary judgment.