The Emerging Battlefield: Should the Use of a Nonmonotonic, Non-Threshold Dose-Response Curve for Alleged Endocrine-Disrupting Chemicals Survive a Daubert/Frye Challenge?

Article excerpt

IN Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses, (1) the authors contend that the toxicological significance of alleged endocrine-disrupting chemicals ("EDCs") cannot be assessed using the traditional monotonic threshold dose-response curve. In contrast, they suggest that EDCs can cause adverse human biological effects at low, regulatory-approved dose levels. Although this article only focuses on biological effects per se and not on whether the effect is adverse or not, they contend that it is improper to extrapolate that harmful effects cannot occur at environmentally relevant, regulatory-approved low-dose levels just because no effects are seen at the much higher regulatory-accepted no observable adverse effect level (NOAEL).

Plaintiffs' attorneys and their retained experts will point to the Vandenberg paper in support of the position that the EDC at issue proximately caused their plaintiff's cancer, reproductive or developmental problem, even when the plaintiff only was exposed to the alleged EDC at the regulatory-approved safe level. Through a weight-of-the-evidence methodology, plaintiffs' experts may attempt to use some sort of nonmonotonic, non-threshold dose-response curve to opine that the health condition at issue generally and specifically was caused by exposure to very low doses of the alleged EDC at regulatory approved levels. Accordingly, defendants must mount a convincing Daubert/Frye argument to defeat this theory.

This article demonstrates how-to construct a successful Daubert/Frye challenge against an expert's attempted use of a nonmonotonic, non-threshold dose-response curve to support an adverse causation opinion about an alleged EDC.

I. Dose-Response Curves

There are three dose-response curves that come into play in any personal injury environmental toxic tort case. First, the traditional monotonic, nonlinear threshold dose-response curve provides that the dose has to reach a recognized threshold level before the chemical likely will have any adverse human health consequences. Once the chemical exerts an adverse effect, the adverse effect will continue to worsen as the dose increases. The generally recognized phrase "the dose makes the poison" is associated with a monotonic, nonlinear dose-response curve.

Second, the monotonic, linear non-threshold dose-response curve states that a chemical can have an adverse human health effect at any dose level. Thus, there is no safe dose level and no threshold dose level. As such, exposure to even one molecule of the chemical at issue puts an individual at risk for the development of an adverse health condition. This concept is referred to as the "one hit theory" because allegedly just one dose of the chemical at any level can start the disease process.

Third, the nonmonotonic, non-threshold dose-response curve, suggested by the Vandenberg article as being particularly applicable to EDCs, provides that a chemical can have effects at regulatory approved low dose levels; have no effects at moderately higher dose levels and have effects at the highest dose levels. A nonmonotonic, non-threshold dose-response curve is described as either Ushaped or inverted U-shaped.

Allowing a plaintiff's expert to opine that the chemical on trial should be analyzed through the use of a nonmonotonic, non-threshold dose-response curve would present significant problems for a defendant. Specifically, the defendant's assertion of the common regulatory compliance defense that the plaintiffs dose level never exceeded the applicable regulatory-acceptable safe dose level would be seriously questioned and could be disregarded completely by the fact finder. Moreover, the plaintiff would be able to raise a significant question in the jurors' minds as to whether the defendant was negligent for only testing the alleged EDC at regulatory-accepted high levels instead of also including in its test protocol environmentally relevant low dose levels. …