Assessing health effects of air pollution The role of controlled studies of human volunteers is examined
complementary relationship of controlled human studies to two other risk-assessment disciplines: animal toxicology and epidemiology. Emphasis is placed upon respiratory irritants common in ambient air, specifically photochemical oxidants and sulfur oxides. A number of other pollutants found in community or occupational environments also may be studied through human exposures, as indicated in Table 1.
Jack D. Hackney William S. Linn Edward L. Avol Environmental Health Service Rancho Los Amigos Hospital School of Medicine University of Southern California Downey, Calif. 90242
To set air quality standards adequate to protect public health, regulatory agencies need extensive, reliable scientific data on the health effects of air pollutants. For short-term stan-
dards especially, much of the necessary information is obtained by observing t h e r e s p o n s e s of h u m a n volunteers who have been exposed deliberately to pollutants under controlled laboratory conditions. Despite its importance in the regulatory process, the field of controlled human studies remains unfamiliar to many in the environmental protection and health professions. This article describes some current problems in assessing health risks from polluted air, the capabilities and limitations of controlled human studies in solving these problems, and the
What are controlled human studies? Human exposure studies require contributions from the disciplines of atmospheric chemistry, environmental engineering, physiology, and clinical medicine. Scientific investigators must create within the laboratory a polluted air environment that is a reasonably realistic model of the polluted ambient environment of concern. They must then recruit volunteer subjects who are representative of the population at risk in the community. The subjects must be exposed to laboratory polluted air under conditions that are well controlled, well documented, and similar to ambient exposure conditions insofar as possible. Finally, the investigators must employ the most sensitive biomedical tests a v a i l a b l e to d e t e c t s u b j e c t s ' responses, if any, to the pollutant dose. As in most medical experiments, subjects' responses to " t r e a t m e n t " must be compared against a control or placebo. Subjects should be "blind" to the difference between the actual exposure and control conditions, as should the experimenters who are actually measuring the results. Otherwise, the expectations of the people involved, or experimental stresses other than the pollutant itself, may provoke responses that could be mistaken for adverse effects of the polluEnviron. Sci. Technol., Vol. 18. No. 4, 1984
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Table 1
Common ambient air pollutants studied by controlled human exposures Substance
NAAQS
a
"High" ambient concentrations
b
Effects reported in controlled human studies
o3
0.12 ppm
