Antarctic over highly populated areas of Australia, New Zealand, South America, and Africa; from the Arctic, ozone-depleted air flows southward over North America and Europe. During these periods, which last for several months, ultraviolet radiation can increase by as much as 20 percent. Exposure to ultraviolet radiation is associated with a variety of adverse health effects (Miller, 1993). The incidence of melanomas has already increased by 83 percent in the United States during the period from 1982 through 1989, and the incidence of skin cancer will continue to increase with continued depletion of the ozone layer (CDC, 1995; Chivian et al., 1993; Longstreth, 1990). Low-intensity ultraviolet radiation (UV-B) from sunlight also alters T-lymphocyte function, thus suppressing cellular immunity and increasing susceptibility to carcinogenic and infectious agents (Daynes, 1990; Hersey et al., 1983). Studies of fishermen on the Chesapeake Bay have demonstrated an increased risk for cataracts associated with exposure to sunlight, an outcome believed to be related to oxygen free radicals generated by UV-B (Chivian et al., 1993; Hu, 1990; Jacques and Chylack, 1991; Rosenthal et al., 1988; Taylor, 1990).

A number of global environmental conditions have the potential for untoward effects on health, and further research is needed to illuminate these potential outcomes. Nurses who are knowledgeable about global environmental conditions, such as ozone depletion, can educate the public about measures to reduce or eliminate their exposure to such hazards, (e.g., by limiting direct exposure to the sun and through the use of sunglasses that limit transmission of ultraviolet radiation) and measures to limit further global changes that may have adverse effects on human health (e.g., by using public transportation or car-pooling when possible to reduce the production of greenhouse gases).

VULNERABLE POPULATIONS

Individuals vary widely in their susceptibility to adverse health effects following exposure to toxic substances. Personal characteristics such as age, gender, weight, genetic composition, nutritional status, physiologic status (including pregnancy), preexisting disease states, behavior and lifestyle factors, and concomitant or past exposures may all affect human responses to environmental conditions. The manner in which these characteristics may enhance or decrease susceptibility to environmental hazards is in some cases fairly obvious, while in others it is less so. The relationship of age and genetic factors to one's susceptibility to adverse effects from environmental hazards are perhaps least obvious to clinicians. Table 2.3 summarizes some of the major genetic factors that may be associated with enhanced susceptibility to chemicals in the environment (Tarcher, 1992). The unique vulnerabilities of individuals at the



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