A Regulatory Precedent for Hormesis

Gary E. Marchant, Ph.D., Associate Professor

Arizona State University College of Law

P.O. Box 877906

Tempe, AZ 85287-7906

Phone: 480-965-3246

Fax: 480-965-2427

Email: gary.marchant@asu.edu

A growing body of scientific evidence suggests that some otherwise toxic agents may have a health protective effect at very low concentrations. The regulatory and legal implications of these findings of 'hormesis' are just now beginning to be evaluated systematically, and Professor Frank Cross has provided a valuable 'first cut' of these issues. As Cross and others have noted, regulators have to date been resistant to incorporate hormesis into regulatory decision-making, although there have been few if any specific regulatory proceedings in which hormesis arguments have been squarely and fully presented.

At least four conditions are necessary for hormesis to have significance in regulatory decision-making. First, there must be credible scientific evidence of a hormetic effect for the specific agent being regulated. Second, hormesis must be relevant to the regulatory decision, in that the regulatory outcome might be different if hormesis is considered. Third, the agency's statutory authority must not preclude consideration of hormesis. Fourth, the regulatory agency must be receptive to considering hormesis.
This Commentary addresses only the last of these four conditions, by evaluating whether agencies are likely to be amenable to considering hormesis, and how reluctant agencies may be forced to consider valid hormesis evidence through the mechanism of judicial review. Specifically, this Commentary discusses a regulatory precedent (or at least analogy) for hormesis, in which the Environmental Protection Agency (EPA) refused to consider the health benefits of ozone in setting a national ambient air quality standard for ozone. Like hormesis, this example involved a substance that is clearly hazardous at higher concentrations, but which may have a net beneficial effect on health at lower concentrations. Like hormesis, the health benefits of low-level ozone appears counter-intuitive and engender considerable initial skepticism from both lay and expert audiences. And, like hormesis, these policy and political factors are likely to cloud and complicate the scientific and regulatory consideration of potential health benefits from low-level exposures.

EPA's Ozone Proceeding

In 1997, EPA revised the ambient air quality standard for ozone from a one-hour average of 0.12 ppm to an eight-hour average of 0.08 ppm. Under the Clean Air Act, EPA was first required to prepare a 'criteria document' that 'accurately reflect[s] the latest scientific knowledge useful in indicating the kind and extent of all dismissed as a trivial thing,' and therefore would need to be addressed in the rulemaking, but at some other time. Nevertheless, when EPA proposed its ozone standard over two years later, there was no discussion of the health benefits of ozone in the proposed regulation, and EPA had not weighed the health benefits of ground-level ozone against the health risks in setting the proposed standard.

In its response to public comments on this issue, and in a subsequent judicial challenge to EPA's decision, EPA asserted two principal defenses of its disregard of the health benefits of ozone. It first argued that the statute prohibited the Agency from considering these health benefits. Yet, the Clean Air Act expressly requires that EPA consider 'all identifiable effects on public health' associated with the presence of a pollutant in the ambient air. In the resulting American Trucking decision,7 the D.C. Circuit Court of Appeals rejected EPA's legal argument, holding that the statute is unambiguous and 'all' means all. The court went further and held that even if the statute were ambiguous, EPA's interpretation excluding consideration of health benefits would surely be unreasonable. In the words of the court, 'it seems bizarre that a statute intended to improve human health would, as EPA claimed at argument, lock the agency into looking at only one half of a substance's health effects in determining the maximum level for that substance.'

The court also rejected EPA's alternative argument that the health benefits of ground-level ozone were too uncertain or insignificant to be considered, stating that 'we can see no reason for imposing a higher information threshold for beneficent effects than for maleficent ones.' The health risks of ground-level ozone were also very uncertain, but that did not stop EPA from relying on its best estimates of those risks notwithstanding the substantial uncertainty. The court concluded that it need not address EPA's arguments that the comments and studies submitted to EPA inflated the health benefits of ground-level ozone given that EPA had improperly chosen 'to give the studies no weight at all.'

Although EPA appealed other parts of the D.C. Circuit's decision to the Supreme Court, it did not appeal the Court's holding that EPA must consider the health benefits of ozone, likely because this was the only portion of the case on which the judges were unanimous. EPA is therefore required to commence a new proceeding to consider the health benefits of ozone.

Lessons for Hormesis

This case study of EPA's treatment of the health benefits of ozone may serve as a useful precedent for regulatory consideration of hormesis. First, this example shows that regulatory agencies are likely to be highly resistant to considering hormesis, because it represents a departure from the traditional conception of, and methodology for evaluating, toxic substances. Health benefits of toxicants may also be perceived as contrary to the agency's internal mission of reducing toxic substances as low as possible. Second, it shows that hormesis, like the health benefits of ozone, will only have force in the regulatory process if it is supported by credible, compelling scientific evidence. Third, it suggests that judicial review may provide an effective mechanism for forcing regulatory agencies to give appropriate consideration to hormesis. Indeed, the court's statement in American Trucking that 'it seems bizarre that a statute intended to improve human health' would disregard the health benefits of a substance would appear to be directly pertinent to hormesis.


1. 42 U.S.C. § 7408(a)(2).

2. 42 U.S.C. § 7409(b).

3. Seckmeyer G, McKenzie RL. Increased ultraviolet radiation in New Zealand (45o S) relative to Germany (48o N). Nature 1992; 359: 135-137.

4. Frederick JE, Koob AE, Alberts AD, Weatherhead, EC Empirical studies of tropospheric transmission in the ultraviolet: broadband measurements. Journal of Applied Meteorology 1993; 32: 1883-1892.


5. Galindo I, Frenk S, Bravo H. Ultraviolet irradiance over Mexico City." Journal of Air & Waste Management Association 1995; 45: 886-892.

6. Lutter R, Wolz C. UV-B screening by tropospheric ozone: implications for the national ambient air quality standard. Environmental Science & Technology 1997; 31:142A-146A.

7. American Trucking Associations v. U.S. Environmental Protection Agency, 175 F.3d 1027 (D.C. Cir. 1999).