Academic journal article Defense Counsel Journal

Sources of Proof of Causation in Toxic Tort Cases

Academic journal article Defense Counsel Journal

Sources of Proof of Causation in Toxic Tort Cases

Article excerpt

ONE OF THE most difficult tasks facing courts and counsel in toxic tort cases is determining effective and admissible sources of proof of causation. Scientific sources are the fields of toxicology and epidemiology. What forms of proof from scientific fields have the courts allowed? And what are some of the goals of direct and cross-examination of experts?


Defendants have had mixed success in excluding expert opinions based on animal and in vitro studies. One of the problems is that animal studies are routinely relied on by the scientific community in assessing the carcinogenic effects of chemicals on humans, and they are regularly used and relied on by various government agencies for regulating purposes. For example, the Food and Drug Administration requires that all drugs be tested in animal bioassays before they can be administered to humans.

The primary objections to the use of animal studies to prove causation are (1) the inherent problem of extrapolating from animals to humans and (2) the difficulty and uncertainty involved in extrapolating from the high dosages required to elicit effects in animal studies and the low-level exposure usually encountered by humans in the environment.

The objection to in vitro studies is that they are static tests performed in a test tube rather than in a living animal. A chemical or drug ingested by an animal usually is broken down by the body and excreted in large measure. Living animals also have the ability to repair themselves. In comparison, mammalian cells exposed to a chemical agent in a test tube have a higher level and duration of exposure to the chemical agent, and they do not have the same ability to repair themselves.

An examination of the cases shows that the courts have not established any uniform rules concerning the admissibility of animal and in vitro studies. Admissibility in any given case often depends on such factors as (1) how the jurisdiction views the reliability of animal and in vitro studies; (2) whether the courts in the particular jurisdiction have admitted or excluded animal and in vitro studies in other toxic tort cases; (3) whether the probative value of the studies is outweighed by the undue prejudice which may result, as required by Rule 403 of the Federal Rules of Evidence; (4) the concessions that can be obtained from plaintiffs' experts regarding the need for epidemiological evidence to confirm animal and in vitro studies; (5) the availability and results of epidemiological studies; and (6) whether the scientific or medical community generally relies on animal or in vitro studies to establish causation between a particular disease and exposure to the chemical in question.


As courts have struggled over time to understand the technical issues involved in proving causation in toxic tort cases, epidemiological studies, which at one time were rejected by the courts, now sometimes is demanded.(1)

In 1984 in Ferebee v. Chevron Chemical Co.,(2) the D.C. Circuit held that a

cause-effect relationship need not be clearly es-

tablished by animal or epidemiological studies

before a doctor can testify that in his opinion,

such a relationship exists. As long as the basic

methodology employed to reach such a conclu-

sion is sound, such as tissue samples, standard

tests and patient examination, products liability

law does not preclude recovery until a statisti-

cally significant number of people have been in-

jured or until science has had the time and re-

sources to complete sophisticated laboratory

studies of the chemical.

But in Richardson v. Richardson-Merrell Inc.(3) the court backtracked from that position somewhat. To distinguish Ferebee, it stated:

Thus, Ferebee stands for the proposition that

courts should be reluctant to alter a jury's ver-

dict when the causation issue is novel and

"stand[s] at the frontier of current medical and

epidemiological inquiry. …

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