Recent decisions have excluded plaintiffs’ expert opinions that fail to estimate actual exposure and prove it was sufficient to cause injury.

By Christine G. Rolph and Laura J. Glickman

Recent federal court rulings in toxic tort litigations have stressed the importance of the dose-response relationship and the need to carefully evaluate the level of exposure to pass the Daubert standard for expert witness admissibility under the Federal Rules of Evidence 702. Under the Daubert standard, courts must assess whether the reasoning or methodology underlying the expert testimony is scientifically valid and whether those reasons or methodologies can be properly applied to the facts at issue. Dose-response methodology studies the relationship between the quantity of a substance (dose) and its overall effect (response) on a person, and is “the hallmark of basic toxicology.”[1] The courts continue to scrutinize experts’ dose-response analysis to determine the reliability of that testimony on specific causation. The following three cases highlight the importance of a thorough dose-response analysis in any expert opinion that evaluates a plaintiff’s exposure and harm.

1. Williams v. Mosaic Fertilizer, LLC[2]

In Williams, a homeowner brought a toxic tort suit against a factory operator for alleged emissions of a number of toxic substances, including sulfuric acid, phosphoric acid, fluoride, and ammoniate phosphates. The homeowner claimed that the emissions caused or exacerbated her medical conditions. The Eleventh Circuit affirmed the district court’s decision excluding the opinions of the plaintiff’s toxicology expert. The district court had found the toxicologist’s opinions unreliable because the toxicologist (1) “neglected the hallmark of the science of toxic torts—the dose response relationship,” and (2) relied on regulatory standards to determine dose without justification.[3]

Specifically, the toxicologist had relied on two academic studies measuring the ambient air concentration of pollutants in the area in which the plaintiff lived to estimate the dose she received and on the EPA’s National Ambient Air Quality Standard (NAAQS) to establish the dose threshold above which her conditions would likely result from her exposure. This methodology of relying on generalized studies failed to properly assess dose-response with regard to the specific plaintiff. According to the court, the toxicologist did not demonstrate that the generalized dose-response relationship would likely produce, contribute to, or exacerbate the plaintiff’s conditions. Moreover, the toxicologist’s assumption that exposure to sulfur dioxide at long-term concentration exceeding the NAAQS of 75 parts per billion established causation ignored the difference in purpose between regulatory standards and toxicological dose-response calculations. The Eleventh Circuit stated: “[R]egulatory 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).”[4] Although the toxicologist alleged that the plaintiff’s genetic disorder caused her to be more sensitive to exposure than the average person, the toxicologist never quantified how much more sensitive she was, and without such information, the court found that the toxicologist could not rely on the NAAQS.

2. Doolin v. Ford Motor Company[5]

This Florida case addressed tort claims related to pericardial mesothelioma, allegedly due to the decedent’s exposure to chrysotile asbestos. The court excluded the opinions of the plaintiff’s expert pulmonologist, which focused on specific causation. The pulmonologist had concluded that even brief, low levels of occupational or para-occupational exposures are “orders of magnitude” greater than background levels, such that those exposures “contribute to the risk of developing mesothelioma.”[6] This is sometimes referred to as the “any exposure” theory. To determine whether that theory was reliable, the court relied on established scientific criteria for proving causation between a chemical exposure and a particular illness. This included an examination of (1) the chronological relationship between exposure and effect biologically plausible (specific causation), and (2) the likelihood that the chemical caused disease in an individual, given other known causes.

In excluding the expert’s opinion, the district court noted that although the pulmonologist acknowledged that mesothelioma was a dose-response disease, the expert failed to analyze the decedent’s particular exposure or the degree to which it increased his risk of mesothelioma. Moreover, the pulmonologist’s opinions failed to identify or discuss the decedent’s particular form of mesothelioma and its connection to asbestos exposure. Finally, the pulmonologist failed to conduct any analysis with regard to the likelihood that asbestos exposure caused the decedent’s mesothelioma given other known causes, including the decedent’s therapeutic radiation to treat lymphoma.

3. York v. BNSF Railway Company[7]

In this Colorado case, a former railroad conductor/brakeman brought a toxic tort suit against a railroad company, claiming that on-the-job exposure to benzene and asbestos caused his bladder cancer. The court excluded as unreliable the opinions of the plaintiff’s expert oncologist, which focused on alleged specific causation. The oncologist’s opinions were based on approximately five hours of research on the effects of diesel exhaust and asbestos and a review of the plaintiff’s medical records. However, the court noted that the oncologist did not consider the plaintiff’s actual exposure or estimate of dose. He also did not review any data reflecting the conditions at the railroad, test or examine the plaintiff, or recount how the plaintiff’s work routine personally affected his health: “As the report stands, [the oncologist] could swap out the plaintiff’s name for that of any other ex-railroad employee with bladder cancer and the information contained therein would be functionally identical and equally inoperative as to specific causation.”[8] The court concluded that the work the expert did perform was “not a reliable procedure subject to scientific scrutiny, but merely a means to affirm a pre-determined conclusion.”[9]


As these three toxic tort cases demonstrate, courts require experts to demonstrate specific dose-response relationships to plaintiffs to surpass the Daubert standard for expert testimony admissibility. An expert’s testimony on specific causation will likely be excluded if the expert fails to both estimate the plaintiff’s actual exposure to the toxic substance and to prove that such amount was sufficient to cause the plaintiff’s injury.


[1]McClain v. Metabolife Int’l, Inc., 401 F.3d 1233, 1242 (11th Cir. 2005).
[2] 889 F.3d 1239 (11th Cir. 2018).
[3] Id. at 1243-44.
[4] Id. at 1247.
[5] 2018 WL 4599712 (M.D. Fla. Sept. 25, 2018).
[6] Id. at *6.
[7] 2019 WL 764574 (D. Colo. Feb. 21, 2019).
[8] Id.  at *7.
[9] Id.