Toxic torts seem to have exploded in the past twenty years or so. This is in large part because of the complex factual and legal context of many toxic tort litigation matters. Most of the major issues presented by toxic torts arise as a result of two basic concepts in nearly all matters. First, the large number of plaintiffs, defendants and jurisdictions involved when a toxic substance allegedly causes harm. Secondly, difficulties are inherent in proving both product identification, as well as medical causation.

The issue of product identification tends to be very fact specific. However, issues of medical causation are handled very differently in Federal and State courts.

Federal Cases

Epidemiologic evidence in toxic tort cases has become more and more important. For example in In re: Breast Implant Litigation, 11 F. Supp.2d 1217 (d. Colo. 1998) the court states that “epidemiology is the best evidence of causation in the mass torts context. The emerging trend in the federal courts has been to exclude scientific evidence that shows a connection between exposure and injury that does not demonstrate a relative risk of 2.0 or greater. See Daubert v. Merrill Dowe Pharmaceuticals, 43 F.3d 1311, 1316 (Ninth Circuit 1995). Post Daubert courts have held that, in order for experts’ opinions about causation to be relevant and admissible, the experts must base their testimony on epidemiological studies which show that the product in question at least doubles the risk of the disease from which the plaintiffs allegedly suffer.

In addressing this requirement, the court has created two separate tests. The first employs the reliability standard set forth in Daubert to label any study with a relative risk, but lower than 2.0, as unreliable. See In re: Breast Implant Litigation at 1225. The second way of addressing this requirement has been to combine the relevance requirement from Daubert with the more likely than not burden present in tort law.

In general, experts that attempt to show causation through case studies, rather than epidemiologic studies, are usually unsuccessful. This is in large part because the case study displays report circumstances among a certain group and do not compare it to the rate at which these circumstances occur among the general population. See e.g. KC v. Ohio Medical Products, 877 F. Supp. 1380, 1385 (N. D. Cal. 1995), Hall v. Baxter Healthcare, 947 F. Supp. 1387 (D. Oregon. 1996).

The reference manual on scientific evidence also addresses epidemiology. The manual presents three questions when assessing such evidence: 1) were the research methods trustworthy; 2) if so, is exposure to the agent associated with the disease; and 3) if the agent is associated with the disease, is it a causal relationship. Linda Bailey, et al. “Reference Guide on Epidemiology” in Reference Manual of Scientific Evidence FJC, 1994 at 131.

State Cases

Washington courts have rejected the requirement that causation must be proven with epidemiological test. Not to say that those tests are irrelevant, but rather, that the plaintiff need not, necessarily prove that exposure to a specific product causes a particular injury with epidemiological evidence.

Expert opinions based on controversial scientific theories are admissible so long as the expert’s techniques and methodologies are sound. Reese v. Stroh, 74 Wn.App. 550, 874 P.2d 200 (1994). The court reasons that, so long as the expert’s knowledge is based on what is known, it is likely admissible. The court continues its analysis by reinforcing the requirement that the expert’s methodology is sound, the expert need not support his conclusion with epidemiological studies.

In Bruns v. Paccar, Inc., 77 Wn.App. 201, 890 P.2d 469 (1995), the court held that plaintiffs need not identify a specific chemical to show a design defect in the toxic tort products liability case. Rather, they must simply show that the alleged unsafe condition proximately caused their injuries. The expert must provide proof that the defect, “more probably than not” caused the injuries. The court then expressly rejected the proposition that only epidemiological evidence is necessary before liability could be found. The Court stated, “[w]hile studies would strengthen an expert’s testimony on causation, the competence of expert testimony does not depend on the existence of such studies.” Id. at 216.

It is clear that epidemiological studies are a vital piece of evidence in most toxic tort cases. Without this type of evidence, causation is incredibly difficult to prove.