Are Expert Witnesses The Backbone Of Toxic Torts?

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Written By: Ryan Jones
Articles Editor, American Journal of Trial Advocacy

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.”[1]  The 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.’”[2]  Pursuant to the Daubert standard, “courts must assess whether the reasons or methodology underlying the expert testimony is scientifically valid and whether those reasons or methodologies can be properly applied to the facts at issue.”[3]  However, one specific issue that courts continue to dissect is the reliability of expert’s testimony on specific causation to the alleged injury.[4]

I. The Daubert[5] Standard

          First, what is the Daubert standard?  The Daubert standard is the “set of criteria used to determine the admissibility of expert witness testimony in federal court.”[6]  However, not just anyone can be an expert witness.  Pursuant to the Federal Rules of Evidence, an expert witness is qualified as such due to:

knowledge, skill, experience, training, or education [and] may testify in the form of an opinion if: (a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert has reliably applied the principles and methods to the facts of the case.[7]

          Trial judges serve as the “gatekeeper” who determines whether an expert’s evidence is deemed to reputable and relevant.[8]  To help reach a conclusion, “judges assess whether the expert testimony is (1) based on scientifically valid reasoning and (2) whether it has been properly applied to the facts at issue.”[9]  Overall, the Daubert guidelines consist of the following factors of consideration: “(1)Whether the theory or technique in question can be and has been tested, (2) Whether it has been subjected to peer review and publication, (3) Its known or potential error rate, (4) The existence and maintenance of standards controlling its operation, [and] (5) Whether it has attracted widespread acceptance within a relevant scientific community.”[10]   If the trial court deems the expert’s testimony to be unacceptable, then that testimony is excluded from the case.  Thus, in a toxic tort case if the expert testimony is deemed to be inadmissible, the ability to link the specific causation of the toxic substance to the injury will be very difficult.  In a toxic tort case, making sure that one’s expert witnesses’ testimony is going to be permitted might be the difference between winning and losing.  James Ray, an environmental litigator and partner at Robinson & Cole, is of the opinion that “[toxic tort] cases are won or lost at the Daubert stage.”[11]

II. Causation in Toxic Tort Cases

          For personal injury cases, which is what a toxic tort case falls under, a plaintiff must prove “the defendant’s conduct caused an event, and that the event caused the plaintiff to suffer compensable damages.” [12]  Which then, the “plaintiff must then show the causal link between the event and the injury by competent evidence.”[13]  The expert’s testimony must show the “causal connection between the defendant’s negligence and the injuries and it cannot be based on mere conjecture, speculation or possibly.”[14]  The evidence that is produced by the expert’s testimony, must not be certain, but rather “rest in reasonable medical probability.”[15]  In toxic tort cases there is (1) general causation and (2) specific causation.[16]  General causation turns on whether or not the substance at issue is capable of causing the particular injury or condition, while specific causation is the analysis of whether or not the substance actually caused the particular plaintiff’s injury.[17]  For specific causation, the plaintiff will need clear scientific and medical testimony from experts linking the toxic chemical to the illness or injury.[18]  However, specific causation is where plaintiff’s tend to run into problems because “in many cases it is impossible to present direct evidence that the substance caused the plaintiff’s injury.”[19]  

          This is a difficult burden to satisfy because there are many factors—possibly, even multiple different types chemicals—individuals are exposed to throughout life that could cause the disease or illness.  For example: “[P]laintiff argues that chemical exposure caused a certain cancer, you’d have to look at all the factors that could cause that cancer, including genetics, lifestyle, and other relevant factors.  That’s in addition to examining whether the chemical causes the cancer in the [dose] amount to which the plaintiff was exposed.”[20]  Thus, because every person lives different lifestyles and their body reacts differently, proving that the specific chemical caused the illness is a challenging burden.  One of the many reasons that this is such a difficult task is because most of the time, the issue is about chemical exposure that occurred years ago.  Regardless, if the plaintiff cannot prove the specific causation, then there will be a defense verdict, no matter how significant the injuries and damages are.

III. Case Illustrations that highlight the Important of Dose-Response Analysis

1) Williams v. Mosaic Fertilizer, LLC[21]

          In Williams, a homeowner brought a toxic tort suit against a factory operator, alleging that the emissions of toxic substances from the factory caused or exacerbated various medical conditions from which the homeowner suffered, including pulmonary hypertension.[22]  The district court found that the toxicologist’s opinions were 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.[23]  In regard to the dose relationship, the toxicologist relied on two academic studies measuring the ambient air concentration of pollutants in the area which the plaintiff lived.[24]  However, the court found that the “generalized studies failed to properly assess the dose-response with regard to the specific plaintiff.”[25]  As a result, the court found that “the toxicologist did not demonstrate that the generalized does-response relationship would likely produce, contribute to, or exacerbate the plaintiff’s conditions.” [26]  Thus, the court did not allow the expert testimony into evidence.[27]

2) York v. BNSF Railway Company[28]

          In York, a former railroad conductor/brakeman brought a toxic suit against railroad company, claiming that on-the-job exposure to benzene and asbestos caused his bladder cancer.[29]  The oncologist based his opinions on “approximately five hours of research on the effects of diesel exhaust and asbestos and a review of the plaintiff’s medical records.”[30]  While the court noted, that the oncologist did focus on specific causation, the court found that the oncologist did not consider the plaintiff’s actual exposure to the dangerous chemicals or estimate of dose.[31]  Further, the oncologist failed to “review any data reflecting the conditions at the railroad, test or examine the plaintiff, or recount how the plaintiff’s work routinely affected his health.”[32]  Therefore, the court noted that “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.”[33]  As a result, the court concluded that the work performed by the expert was “not a reliable procedure subject to scientific scrutiny, but a [sic] merely a means to affirm a pre-determined conclusion.”[34]

IV. Conclusion

          Overall, one of—if not the most important—things in toxic tort case is the expert witness. Expert witnesses are necessary to link the chemical or dangerous substance to the specific injury that is alleged by the plaintiff.  Said expert must conduct analysis to determine (1) whether the substance has the potential to cause such injury, and (2) whether or not the substance actually caused the injury that the plaintiff is alleging.  If the expert is unable to produce scientific evidence that the substance caused the injury, then there will more than likely be a defense verdict.  However, if the expert is able to link the substance to the injury, it could be a very rewarding day for the plaintiff.

[1]Chrisine Rolph, Satisfying ‘Daubert’ in Environmental Toxic Tort Litigation, environmental litigation, (November 22, 2019),

[2] Id.

[3] Id.

[4] Id.

[5] Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579 (1993).

[6] Anjelica Cappellino, The Daubert Standard: A Guide To Motions, Hearings, and Rulings, Expert Institute,(September 2, 2020), 

[7] Fed. R. Evid. 702 (2020).

[8] Cappellino, supra note 5.

[9] Id.

[10] Id.

[11] Why Toxic Torts are hard to Litigate and Win, A.B.A.  J., (November 1, 2018, 12:15AM),

[12] Dawn Smith, Toxic Torts: How Do I Prove Medical Causation?, Attorney At Law Magazine, (September 14, 2018),,to%20disqualifying%20a%20plaintiff’s%20claim (citing Burroughs Wellcome Co. v. Crye, 907 S.W.2d 497, 499 (Tex. 1995)).

[13] Id. (citing Guevara v. Ferrer, 247 S.W.3d 662, 666 (Tex. 2007)).

[14] Id. (citing Park Place Hosp. v. Milo, 909 S.W.2d 508, 511 (Tex. 1995)).

[15] Id. (citing Burroughs Wellcome Co., 907 S.W.2d 497, 500 (Tex. 1995)).

[16] Id. (citing Merrell Dow Pharm. v. Havner, 953 S.W.2d 706, 714 (Tex. 1997)).

[17] Id.

[18] Id.

[19] Id.

[20] Supra note 10.

[21] 889 F.3d 1239 (11th Cir. 2018).

[22] Id. at 1242.

[23] Id. at 1243.

[24] 1246.

[25] Rolph, supra note 1.

[26] Id.

[27] Williams, 889 F.3d at 1246.

[28] No. 1:17-cv-1088-RM-STV, 2019 WL 764574 (D. Colo. Feb. 21, 2019).

[29] Rolph, supra note 1.

[30] Id.

[31] Id.

[32] Id.

[33] York, 2019 WL 764574 at *7.

[34] Id.

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