Vermin of Proof: Arguments for the Admissibility of Animal Model Studies as Proof of Causation in Toxic Tort Litigation

• Author: Kristen Ranges/Jessica Owley
• Position: PhD Candidate, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami; JD 2020 from University of Miami School of Law/Professor, University of Miami School of Law, Environmental Law Program Director
• Pages: 303-350

Vermin of Proof: Arguments for the Admissibility of

Animal Model Studies as Proof of Causation in

Toxic Tort Litigation

KRISTEN RANGES* AND JESSICA OWLEY**

ABSTRACT

Toxic torts is a body of law that aims to compensate individuals for

harms they suffer from exposure to hazardous substances. To successfully

bring a toxic tort claim, a plaintiff must prove the main elements of a gen-

eral tort cause of action: duty, breach, causation, and damages. Causation

in a toxic tort case is particularly challenging to prove given the nature of

toxic substances. To prove the toxicant in question caused the damages

alleged, plaintiffs often present expert testimony based on scientific stud-

ies. Animal model studies, in particular, can help factfinders understand

the health implications of the toxicants at issue. However, judges, scholars,

and other legal professionals are skeptical of the use of animal studies

because of scientific and legal concerns, which range from interspecies

disparities to prejudice of juries. These concerns are either unfounded or

exaggerated. Animal model studies can be both reliable and relevant in

toxic tort cases. Given the Federal Rules of Evidence, case law relevant to

scientific evidence, and one of the goals of tort law—justice—judges

should more readily admit these types of studies as evidence to help plain-

tiffs meet the burden of proof in toxic tort litigation.

TABLE OF CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304

I. Toxic Torts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

* PhD Candidate, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of

Miami; JD 2020 from University of Miami School of Law. © 2022, Kristen Ranges and Jessica

Owley. We would like to thank David Takacs and Martin Grosell for their guidance and Donna

Coker, Robin Craig, Joe Dellapenna, Blake Hudson, Katy Kuh, Sean Lyness, Anthony Moffa,

Mike Pappas, Bill Piermattei, Joshua Sarnoff, Gabe Scheffler, and Stephanie Stern for their

comments.

** Professor, University of Miami School of Law, Environmental Law Program Director.

Affliated Faculty, Rosenstiel School of Marine, Atmospheric, and Earth Science, Department of

Environmental Science and Policy and Abess Center for Ecosystem Science and Policy at the

University of Miami.

303

A. Basics of a Toxic Tort Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

B. The Causation Hurdle in Toxic Torts . . . . . . . . . . . . . . . . . . . . . . 308

II. Admissibility of Scientific Evidence . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

III. Scientific Studies Used to Make Causal Connections . . . . . . . . . . . . . . . 321

A. Non-Animal Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

B. Animal Model Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

IV. Admitting Animal Model Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

A. Scientific Validity of Animal Studies . . . . . . . . . . . . . . . . . . . . . . 326

1. Species Disparities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

2. Housing and Husbandry of Test Subjects . . . . . . . . . . . . . . . . 330

3. Response Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

4. Subsequent Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

5. Scaling and Extrapolation Calculations . . . . . . . . . . . . . . . . . 335

B. Animal Studies are Legally Permissible as Scientific Evidence. . . . 338

1. Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

2. Relevance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

a. Unfair Prejudice, Confusing the Issues, and Misleading the

Jury. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

b. Waste of Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

c. Needlessly Presenting Cumulative Evidence . . . . . . . . . 344

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

INTRODUCTION

Toxic torts is a powerful area of law that provides injured parties with an oppor-

tunity to recover monetary damages from disease, deformity, or death suffered by

themselves or loved ones. These injuries result from exposure to substances (for

example, pregnancy medications, herbicides, dielectric fluids) produced, proc-

essed, distributed, or otherwise controlled by another party. Often, the party is the

toxicant’s manufacturer but may also include safety equipment manufacturers,

chemical or equipment distributors, or owners and lessors of a premises where the

exposure occurred.

In all tort cases, the plaintiff bears the burden of proving the defendant caused

the harm. In toxic tort cases, proving the substance in question more likely than

not injured the plaintiff is challenging. Scientific evidence plays a key role in

establishing the cause of an injury. The most common forms of scientific evidence

in toxic tort cases are human clinical trials, epidemiological studies, chemical struc-

ture-biological activity studies, and animal model studies. The causation hurdle is

heightened by judges’ continued skepticism of a key form of scientific evidence:

animal model studies.

Animal studies provide abundant information about toxic substances and can

help us understand how those substances affect humans. Researchers use animal

model studies—a type of controlled, experimental study—to make inferences

about a substance’s adverse effects on humans. Researchers also use animal studies to

304 THE GEORGETOWN ENVTL. LAW REVIEW [Vol. 34:303

understand basic anatomy and physiology, explore the impacts of environmental stres-

sors, and test experimental treatments. Understanding human health through transla-

tional research using animal models is beneficial because experimentation involving

animals is often more efficient (in both time and resources) than conducting human

experiments or employing other forms of toxicity research, like epidemiological

studies. And although there are ethical constraints, they are few compared to the

ethical concerns arising in human experimentation studies. Importantly, these

benefits do not come at the expense of result accuracy or translational capability,

as skeptics suggest.

Skeptics of animal model studies articulate various scientific and legal con-

cerns about this type of research, especially when it is used in the context of liti-

gation. Some scientific concerns are interspecies disparities, artificial selection,

and interpretation biases, which skeptics argue reduce the validity of the studies’

results because the science is invalid; therefore, the animal studies should

be inadmissible. Critics also argue that animal studies can unfairly prejudice,

confuse, or mislead the jury, as well as waste time by needlessly presenting cu-

mulative evidence. These critiques are unfounded and exaggerated. Critics mis-

understand the science and overstate the limitations of the animal studies. The

Federal Rules of Evidence, relevant case law, and foundational principles of tort

law do not support the outright exclusion of animal studies in toxic tort cases. Yet

courts frequently exclude animal studies for reasons that seemingly amount to an

overall misunderstanding about how animal studies are conducted and inter-

preted, and an inherent bias against their relevance and reliability.

1

Part I of this Article outlines the basic elements of a torts case and includes the

specific causation challenges in toxic torts to illustrate where animal studies could

1. See, e.g., Brock v. Merrell Dow Pharm., Inc., 874 F.2d 307, 314 (5th Cir. 1989) (“. . . the very

limited usefulness of animals studies when confronted with questions of toxicity.”); In re Zoloft

(Sertraline Hydrochloride) Prods. Liab. Litig., 26 F. Supp. 3d 466, 475 (E.D. Pa. 2014) (“. . . causation

opinions based primarily upon in vitro and live animal studies are unreliable and do not meet the

Daubert standard.”); Sarkees v. E.I. DuPont de Nemours & Co., 2020 U.S. Dist. LEXIS 174889 (W.D.

N.Y. Aug. 21, 2020) (granting in full defendant’s motion for summary judgment, disagreeing with the

Report and Recommendation that “precise information concerning the exposure necessary to cause

specic harm to humans and exact details pertaining to the plaintiff’s exposure are benecial, such

evidence is not always available, or necessary, to demonstrate that a substance is toxic to humans given

substantial exposure” (quoting Westberry v. Gislaved Gummi AB, 178 F.3d 257 (4th Cir. 1999)) and that

“some [animal] studies have showed stronger results than others, but the overall body of literature for

several decades has tended in the direction of showing a statistically signicantly higher incidence of

tumors, bladder cancer, or other cancers for animals exposed to [the substance at issue].”); Pinares v.

United Tech. Corp., 2019 U.S. Dist. LEXIS 230033 (S.D. Fla. Oct. 3, 2019) (only briey stating in a

footnote: “The animal studies relied upon by [the expert] are insufcient to show an association . . .”);

Pinares v. United Tech. Corp., 2019 U.S. Dist. LEXIS 230034 (S.D. Fla. Oct. 3, 2019) (only briey

stating in a footnote: “. . . [the experts] reliance on animal studies are insufcient to show causation.”); In

re Abilify (Aripiprazole) Prods. Liab. Litig., 299 F. Supp. 3d 1291, 1310 (N.D. Fla., Mar. 15, 2018)

(stating that animal studies can support general causation opinions if the expert explains how and why

the studies can be reliably extrapolated); Martin v. Crown Equip. Corp., 2016 U.S. Dist. LEXIS 195737

(N.D. Ga. Jan. 5, 2016).

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