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 (± 4 percent) between 1981 and 1991 (224).

The extent to which skin cancer incidence will rise in response is uncertain. Assuming no change occurs in the behavior of the general population, a sustained 10 to 15 percent depletion of stratospheric ozone over several decades, as projected, could result in an stimated 15- to 20-percent increase in the incidence of skin cancer in fair-skinned populations, or about 250,000 additional cases each year (225). This figure is rough, however, since the model does not take into account individual susceptibility and personal behavior, such as wearing sunscreen to minimize exposures. In addition to its link with skin cancer, UV light can cause cataracts. The best current estimate shows that for each 1-percent depletion in stratospheric ozone, cataract incidence would increase by 0.6 to 0.8 percent (226).

Over the past 15 years, animal studies have identified several immunosuppressive effects of UV-B; the few studies that have been conducted on humans lend support to these results (227). Other studies suggest that although dark-skinned people are at less risk of skin cancer, pigmentation does not seem to be protective against UV's effects on the immune system (228). A compromised immune system makes it more difficult to fight off infectious diseases, making UV's immunosuppressive effects potentially some of the most dangerous (229).

References and notes

220. Op. cit. 172, p. 6.

221. M. Prather et al., "The Ozone Layer: The Road Not Taken," Nature, Vol. 381 (1996), p. 554.

222. Steven A. Lloyd, "Stratospheric Ozone Depletion," The Lancet Vol. 342, (November 6, 1993), p. 1156.

223. Op. cit. 97, p. 38.

224. S. Madronich et al., "Changes in Ultraviolet Radiation Reaching the Earth"s Surface," Ambio, Vol. 24, No. 3 (May 1995), p. 148.

225. Op. cit. 97, p. 166.

226. Op. cit. 97, p. 167.

227. Amminikutty Jeevan and Margaret L. Kripke, "Ozone Depletion and the Immune System" The Lancet., Vol. 342 (November 6, 1993), pp. 1159-1160.

228. M. Vermeer et al., "Effects of Ultraviolet B Light on Cutaneous Immune Responses of Humans with Deeply Pigmented Skin," Journal of Investigative Dermatology, Vol. 97 (1991), pp. 732-733.

229. Op. cit. 227.