United States Court of Appeals for the Fifth Circuit United States Court of Appeals Fifth Circuit ____________ FILED May 12, 2025 No. 23-30854 ____________ Lyle W. Cayce Clerk Floyd Ruffin,

Plaintiff—Appellant,

versus BP Exploration & Production, Incorporated; BP America Production Company,

Defendants—Appellees. ______________________________

Appeal from the United States District Court for the Eastern District of Louisiana USDC Nos. 2:20-CV-334, 2:22-CV-1006 ______________________________ Before Elrod, Chief Judge, and Higginbotham and Southwick, Circuit Judges. Jennifer Walker Elrod, Chief Judge: This toxic-tort case arising from the 2010 Deepwater Horizon oil spill presents the issue of what expert testimony must be introduced to establish causation. Plaintiff–Appellant Floyd Ruffin alleges that he was exposed to crude oil while employed as a clean-up worker after the spill. He was later diagnosed with prostate cancer and sued BP. The issue is whether the expert testimony that Ruffin submitted to prove that his alleged exposure caused his cancer was sufficiently “relevant” and “reliable” to be admissible under Case: 23-30854 Document: 90-1 Page: 2 Date Filed: 05/12/2025

No. 23-30854

Federal Rule of Evidence 702 and Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). BP says it was not, arguing for a rule that would require an expert to testify to the specific quantitative amount or “dose” of chemical exposure that would cause the plaintiff’s injury. We decline to adopt such a rule because it conflicts with our precedent. But because we agree with the district court that Ruffin’s expert testimony nevertheless suffers from fatal analytical flaws, we AFFIRM the district court’s exclusion of the testimony and its associated award of summary judgment to BP. I Ruffin worked as a shoreline clean-up worker in Louisiana for five months following the 2010 Deepwater Horizon oil spill. Five years later, he was diagnosed with prostate cancer. Ruffin sued BP in the Eastern District of Louisiana pursuant to the Deepwater Horizon medical-benefits class action settlement as a “Back-End Litigation Option” (BELO) claim for alleged injuries that manifest after the date of the settlement. Ruffin claimed that he was exposed to harmful chemicals that caused his cancer while working on the clean-up effort. After discovery, Ruffin designated several experts. At issue here is Ruffin’s causation expert, Dr. Benjamin Rybicki, who is a genetic and molecular epidemiologist. Rybicki reported that Ruffin was exposed to “polycyclic aromatic hydrocarbons” (PAHs)—chemical compounds that are “ubiquitous in the environment” and occur “in coal, peat, crude oil, and shale oils”—and that at least one of these compounds can cause prostate cancer. Rybicki pointed specifically to a compound called “benzo(a)pyrene,” the “most prevalent PAH,” and reported that it causes cancer in humans. Relying on animal studies and occupational studies, Rybicki concluded that occupational exposure to PAHs is associated with a “modest” 1.5- to 2-fold increase in one’s risk of prostate cancer.

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