Until recently, concern about industrial pollution has centered on its direct toxicological effects. Yet, researchers have begun to understand that pollutants can also affect humans indirectly, through large-scale ecological disruptions.
Like PCBs, chlorofluorocarbons (CFCs) were first synthesized in 1930 and were quickly hailed as safe alternatives to ammonia and other coolants prone to leaks and explosions (220). CFCs were used extensively as refrigeration and air-conditioning fluids, aerosol propellants, solvents, and fire suppressants. Since then, however, it has become evident that these long-lived chemicals are primarily responsible for the progressive depletion of the stratospheric ozone layer. The most dramatic manifestation of ozone depletion is the springtime ozone hole over Antarctica, first discovered in 1985.
In response to stratospheric ozone depletion, the international community negotiated the Montreal Protocol in 1987 to phase out production of ozone-depleting substances. The treaty required developed countries to end the production of most ozone-depleting substances by January 1996. Developing countries were allowed to increase the production of CFCs until 1999, after which their production must be cut progressively until it ends in 2010. However, even assuming that the Montreal Protocol is fully implemented, the concentration of stratospheric ozone is not expected to return to its normal level until the second half of the next century (221).
The major significance of stratospheric ozone depletion for health is reduced shielding of the Earth’s surface against incoming solar ultraviolet radiation, in particular UV-B (222). Efforts to measure the associated increase in ground-level UV radiation are just beginning, but models provide some insight into the expected changes. Under existing conditions, the World Meteorological Association has projected that ground-level UV-B radiation will increase by around 15 percent in winter and spring and 8 percent in summer and autumn in the northern midlatitudes (including countries in North America and Europe). Southern temperate areas are expected to experience ground-level UV-B increases of 13 percent (223). Increased UV-B levels have been documented in some studies for mid- and high-latitude locations. In the Swiss Alps, for instance, scientists recently concluded that ground-level UV-B has increased by 7 (