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Toxicology and the Law Chapter | 11 187

VetBooks.ir courtroom. These concepts are general causation and spe- without further inquiry as to its derivation may erode the
strength of such arguments. It may prove critical to the
cific causation. The discussion of specific causation fol-
lows in the next section.
argument to know whether the regulation was established
“Causation is frequently a crucial issue in toxicology using a “reasonable certainty of no harm” standard or a
cases. Establishing causation means providing scientific “normally renders injurious to health,” or other standard.
evidence from which an inference of cause and effect The former standard may have included various
Reference Manual on Scientific Evidence at 32
may be drawn.” The “uncertainty factors” to extrapolate below measured dose
Manual goes on to describe the process of arriving at gen- response data to obtain a safety standard. These uncer-
eral causation. tainty factors may be explored in a legal venue if one is
testifying to a “reasonable degree of medical certainty”
Once the expert has been qualified, he or she is expected to that the exposure did in fact cause harm, when the basis
offer an opinion on whether the plaintiff’s disease was for the regulatory standard is a “reasonable certainty of
caused by exposure to a chemical. To do so, the expert no harm” obtained using “uncertainty factors.” 43
relies on the principles of toxicology to provide a scientifi- In short, is the alleged chemical capable of causing
cally valid methodology for establishing causation and then the disease observed at any dose or exposure ? In our
applies the methodology to the facts of the case. hypothetical above, has the chemical that was added to
An opinion on causation should be premised on three the feed additive been shown to cause the clinical signs
preliminary assessments. First, the expert should analyze and lesions observed in the species of animal in this case
whether the disease can be related to chemical exposure by ? If not, the expert’s testimony may not be allowed in the
a biologically plausible theory. Second, the expert should case. If so, an analysis of specific causation would most
examine if the plaintiff was exposed to the chemical in a likely be required.
manner that can lead to absorption into the body. Third, the
expert should offer an opinion as to whether the dose to
which the plaintiff was exposed is sufficient to cause the SPECIFIC CAUSATION:
disease.
THE DIFFERENTIAL DIAGNOSIS
Reference Guide on Toxicology at 419
General causation answers the question of whether the
Courts define general causation as “the capacity of a chemical in question may cause the disease observed.
Siharath at xx.
product to cause injury.” General causation is Specific causation is aimed at answering the question of
a scientifically established cause-and-effect relationship. whether the chemical in question did in fact cause the dis-
To satisfy this burden, sufficient testing must be done to ease in the specific case at hand. This concept has been
establish that a disease or condition can arise after expo- stated in a variety of ways. Specific causation is “proof
sure to a certain substance. Peer reviewed literature of that the product in question caused the injury of which the
epidemiology studies, case reports, in vitro, and animal plaintiff complains” Siharath It is a tendency to show that
studies may be used to support a general causation the person’s alleged exposure, in fact, caused his or her
argument. condition. Siharath at See also D.T. Ralston In other words, it is a
A toxic tort plaintiff must first show that the substance showing that said exposure was the actual cause of the
to which he was allegedly exposed is capable of causing injury. See e.g., Raynor An analysis of specific causation
his injury—general causation. See e.g., Raynor 7 General cau- answers the question of whether exposure to the specific
sation asks whether exposure to a substance causes harm chemical in question did or did not cause the disease expe-
to anyone. See Navigating Uncertainty rienced by the plaintiff, or in this chapter’s hypothetical,
Increasingly, the discipline of epidemiology is argued plaintiff’s animals. The specific causation analysis requires
as a basis for general causation. When epidemiology is consideration of other potential causes of the disease.
used to present the incidence and distribution of disease Consideration of other causes of the disease is often
in humans, courts have often ruled the expert opinion referred to as a differential diagnosis. The differential diag-
admissible. This has not always been the case for toxico- nosis may not always be a common occurrence in the prac-
logical expert opinions because of the need to extrapolate tice of both human and veterinary medicine. Differential
from animal, or in vitro, studies to humans. This line of diagnosis evidence is often crucial to show specific causa-
argument may be less persuasive in an animal poisoning tion. See Lennon Without some evidence that the substance in
case when such extrapolations are not needed. question caused the specific injury to the specific plaintiff,
Occasionally experts rely on state or federal regula- courts are likely to grant the defendant summary judgment.
tions to opine that exposure to a certain amount or con-
centration of a chemical is associated with a particular 43. See Ellen K. Silbergeld. The Role of toxicology in causation: A
adverse event. However, merely citing the regulation Scientific Perspective. 1 Cts. Health Sci. & L. 374, 378 (1991).