Ozone depletion and its effects on human populations.

Concern about the ozone-depleting potential of man-made chemicals has led the United Nations to control their usage. Under the present arrangements, fully halogenated chlorofluorocarbons, halons and carbon tetrachloride will be phased out by the year 2000, and methylchloroform by the year 2005. Even so, atmospheric chlorine is expected to rise to seven times its natural level, so further ozone losses and greater ultraviolet B (UVB) exposure can be expected over heavily populated areas of the globe. Calculating changes in skin cancer incidence is a two-stage process which must take account of the increase in biologically effective UVB that results from an ozone loss of 1% (optical amplification factor, OAF) and the percentage increase in skin cancer incidence that results from a 1% increase in annual UV dose (biological amplification factor, BAF). Epidemiological data provide a BAF value of approximately 1.7 for basal cell carcinoma and 3.0 for squamous cell carcinoma. The absorption spectrum of ozone and the increased carcinogenic impact of UV radiation around 300 nm results in a value for OAF of approximately 1.6%; thus a 10% loss of ozone, if sufficiently sustained, would eventually increase the incidence of basal and squamous cell carcinomas by almost 30% and 50%, respectively. Dermatologists, therefore, need to look carefully at the environment in order to safeguard the health of future generations.