Is there a threshold for human health risk from ozone?
The existence of a "threshold," or concentration below which no adverse health effects are observed, is the basis for current air quality standards in the U.S. After using a regional dosimetry model (Miller-Overton) to adjust for variations in animal species, exposure scenario, breathing patterns, etc., measurements of several different toxicity end-points reported by different laboratories were found to lie on a straight line passing through the origin, suggesting the absence of a threshold or no-effect level in animals. On the other hand, the biochemistry of ozone and its detoxification mechanisms suggests that a threshold should exist. Two mathematical population models are examined to illustrate how repair mechanisms affect such thresholds and how a population-wide threshold might not exist The probability of injury can, however, be calculated so that an acceptable level of risk can be chosen. The models also illustrate how specific populations at risk can be identified, in this case for vitamin E deficiency as in cystic fibrosis patients. © 1989 Elsevier Science Publishers B.V.
