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June 14, 2019 Articles

Regulatory Emissions Standards: Unreliable Proof of Causation

Regulatory standards are intentionally overprotective and thus “unreliable predictors” of when exposures to regulated substances become harmful.

By David Weinstein, Christopher Torres, and Ryan Hopper

In Williams v. Mosaic Fertilizer, LLC, the U.S. Court of Appeals for the Eleventh Circuit recently held that regulatory emissions standards are “unreliable predictors” of the dose at which exposures to emissions become harmful to human health. 889 F.3d 1239, 1248 (11th Cir. 2018). The opinion teaches toxic-tort practitioners the valuable lesson that expert general-causation testimony grounded in overprotective regulations might not pass Daubert scrutiny.


Williams involved a Floridian’s allegations that a fertilizer facility’s emissions—particularly, sulfur dioxide—had traveled to her home and caused her to develop adverse pulmonary conditions, including obstructive pulmonary disease. 

Under long-standing Eleventh Circuit precedent [login required], this type of toxic-tort claim requires proof of general causation—that is, proof that the substance at issue is capable of causing the harm alleged. Proof of general causation, in turn, requires expert testimony, which must be grounded in reliable methodologies to be admissible under Daubert v. Merrell Dow Pharmaceuticals, Inc. and Federal Rule of Evidence 702. The most important methodology for general-causation opinions is the dose-response assessment, a scientific estimate of “the dose or level of exposure at which a substance causes harm.” Williams, 889 F.3d at 1246 (quoting McClain v. Metabolife Int’l, 401 F.3d 1233, 1241 (2005)). A dose-response assessment is critical because all substances are potentially toxic; it is the dose that “differentiates a poison from a remedy.” David L. Eaton, Scientific Judgment and Toxic Torts—A Primer in Toxicology for Judges and Lawyers, 12 J.L. & Pol’y 5, 11 (2003) (citation omitted).

In an attempt to prove her claims, Williams retained a toxicologist who opined that her pulmonary problems had been caused by exposure to airborne sulfur dioxide in concentrations exceeding the 75 parts per billion standard established by the National Ambient Air Quality Standards (NAAQS). The NAAQS are outdoor air-quality standards that the Environmental Protection Agency (EPA) sets to control certain emissions that, in its view, “may reasonably be anticipated to endanger public health or welfare.” 42 U.S.C. § 7408(a). Importantly though, the Clean Air Act requires the EPA to set NAAQS at levels that provide for the “protection of public health with an adequate margin of safety.”

District Court Order

Based in part on the margin of safety built into NAAQS levels, the district court excluded the general-causation opinion of Williams’s toxicologist as unreliable. The court reasoned that the “fact that [the EPA] has established 75 ppb as a ‘safe’ level of exposure . . . does not mean that any amount exceeding that standard is necessarily unsafe or toxic.” Williams v. Mosaic Fertilizer, LLC, No. 8:14-CV-1748-T-35MAP, 2016 WL 7175657 [login required]
, at *9 (M.D. Fla. June 24, 2016). The court also granted summary judgment against Williams on all claims that depended on her toxicologist’s unreliable testimony.

Eleventh Circuit Opinion

On appeal, the Eleventh Circuit affirmed and expounded on the “potential methodological perils of relying, at face value, on regulatory emissions levels to establish causation.” Williams, 889 F.3d at 1247. In the court’s view, the “biggest problem” with the toxicologist’s general-causation opinion was his failure to recognize that regulatory standards tend to be protective, not predictive. Id. As the court explained, “regulatory standards often build in considerable cushion in order to account for the most sensitive members of the population and prophylactically protect the public (in other words, they are protective), while dose-response calculations aim to identify the exposure levels that actually cause harm (in other words, they are predictive).” Id. (emphasis in original). For that reason, “facial reliance on regulatory standards,” such as the NAAQS or the reference concentrations in EPA’s Integrated Risk Information System (IRIS), cannot “substitute for scientifically rigorous dose-response assessments.” Id.

 The court clarified that the excluded toxicological testimony was unreliable because of its underlying methodology and not simply its imprecision. Experts need not express their general-causation opinions in “precise numbers,” but they do need to “lay a ‘reliable groundwork for determining the dose-response relationship.’” Id. (quoting McClain, 401 F.3d at 1241, 1241 n.6).


Williams is the latest in a series of three Eleventh Circuit opinions denouncing reliance on regulatory actions to prove causation, and the first to do so in an environmental context. The prior two opinions pertained to pharmaceuticals. In Rider v. Sandoz Pharmaceutical Corp., the Eleventh Circuit determined that the FDA’s disapproval of the drug Parlodel did not “provide scientific proof of causation” in related toxic-tort cases because the FDA’s decision was based on a “risk-utility analysis” that “involves a much lower standard than that which is demanded by a court of law.” 295 F.3d 1194, 1201 (11th Cir. 2002). The Eleventh Circuit reached a similar conclusion in McClain v. Metabolife International, Inc., in which the court held that FDA efforts to restrict the sale of ephedrine-containing supplements spoke to caution rather than causation. 401 F.3d 1233, 1249 (11th Cir. 2005).

At bottom, the lesson from Rider, McClain, and now Williams is that when an expert bases a causation opinion on a regulatory rule, the “trial court”—and the lawyers who practice before it—“should understand what the rule really means about causation for the specific plaintiff, not simply about protecting the public-at-large from risk of harm based on a risk-utility analysis.” McClain, 401 F.3d at 1249. In a circuit where proof of general causation requires admissible expert testimony, the difference can be case-dispositive.

David Weinstein, Christopher Torres, and Ryan Hopper practice at Greenberg Traurig. Torres and Hopper practice in the firm’s Tampa, Florida, office, and Weinstein practices both there and in the firm’s Washington, D.C., office.

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