Fifth Circuit Clouds Threshold Dose Analysis in Ruffin v. BP

Plaintiffs in toxic tort cases must prove both general and specific causation, generally through the testimony of experts. Experts must establish that a specific chemical exposure can (and did) cause the specific injury at issue. In order to make that showing, the plaintiff’s exposure must at least have exceeded the minimum harmful level of the chemical — the “threshold dose.” As the Eleventh Circuit made clear last year in its handling of In re Deepwater Horizon BELO litigation (which we discussed here), threshold dose is a concept that straddles general and specific causation. A more recent BELO case, Ruffin v. BP Exploration & Production, Inc., --- F.4th ---, 2025 WL 1367185 (5th Cir. May 12, 2025), shows how isolating an expert’s general causation opinion from its implications on specific causation can cloud the analysis.