Economists face no fundamental problem in calculating the optimal exposure of a hormetic substance and this could potentially be set as a regulatory level. This level would be where the marginal cost of control is equal to the slope of the exposure-response function. There are a number of reasons, however, to expect public resistance to assuming hormesis. These reasons include the fact that hormesis implies a lower level or risk for any given exposure; it might be viewed as weakening regulatory standards; and it could justify low emissions if marginal costs are low. If all we care about are the negative effects measured by a single health endpoint, then the RfD (the level of exposure below which there is no appreciable risk) may be appropriate. Hormesis maintains the single endpoint, but accepts beneficial as well as deleterious effects. If we are going to accept beneficial effects then we should consider all health endpoints and all costs and benefits. This is simply benefit-cost analysis with a hormetic exposure-response curve. Because of legal constraints, this type of analysis may be of little use in setting tolerance levels, but may be important if the EPA chooses to adopt more voluntary policy measures.

Economic implications of hormesis in policy making.

Economics and hormesis

Professor Cross concludes that "the evidence for hormesis is sufficiently strong that the government should alter its default presumption of linear doseresponse models." Although we do not doubt that hormetic effects have been proven for some substances and some end points, we believe, for several reasons, that Professor Cross's recommendation is unwarranted at this time. Before turning to our reasons for rejecting Professor Cross's proposal, a definitional note is in order. Hormesis is "the stimulatory effect of subinhibitory concentrations of any toxic substance on any organism." Put simply, substances that exhibit hormetic effects may be beneficial to health at low doses but harmful at high doses. Small amounts of vitamin A, for example, are required for human survival, but large amounts are toxic; either exposure extreme, in other words, can be fatal. Many of the substances that have been shown to have a J-shaped dose-response curve a curve

R J Lechleider

Papers

Hormesis and the law.