The Environmental Protection Agency has released a new study suggesting that the Earth's protective ozone layer will remain in jeopardy unless deeper cuts are made in the worldwide production of chlorofluorocarbons (CFC), once widely used in the United States as spray can propellants.
The report projects more severe potential damage to the ozone layer than any major study to date. But it agrees with the others that severe effects -- such as allowing significantly more cancer-causing ultraviolet radiation to reach the ground -- are not likely to occur until well into the next century.
Overall CFC use has dropped in recent years -- chiefly because its use as an aerosol propellant was largely banned in the United States and somewhat restricted in Europe. But its use is still growing in other applications, especially as a coolant in refrigeration and air conditioning systems.
As these devices are discarded, the CFC is usually drained and allowed to evaporate. Although not toxic, it rises into the upper atmosphere and reacts with ozone, a special form of the oxygen molecule, converting it into other substances.
Because ozone molecules absorb an especially deadly portion of the sun's ultraviolet radiation, called ultraviolet-B, fewer ozone molecules mean more ultraviolet-B reaches the ground. Currently almost no ultraviolet-B penetrates the ozone layer.
In addition to causing skin cancers, ultraviolet-B has been found to suppress the immune systyem in laboratory tests on animals, making them more vulnerable to infections. Many researchers say they think the radiation also would damage many plant species. Tests show it is also highly destructive of polymers, found in all forms of plastics and many paints.
In recent years estimates of potential damage to the ozone layer have tended to be more moderate than those of the 1970s, when the danger was recognized. But scientists have never dismissed the threat entirely.
While previous studies assumed a constant level of CFC production, the EPA study takes into account the fact that production is increasing every year.
It projects that if total CFC use continues to grow at a moderate rate of 2.5 percent a year -- near the mid-range of recent growth rates -- the ozone in the atmosphere could be depleted by 26 percent by the year 2075. If, however, the growth rate is 4.2 percent -- the high end of rates that have existed in the past -- 60 percent of the ozone could be destroyed by 2025.
The wide difference in effects takes account of new knowledge about the chemistry of CFC in the atmosphere, showing that the ozone-depletion rate mushrooms exponentially -- faster and faster -- as CFC levels grow at a steady rate.
The EPA study suggests that the first 10 percent of reduction in ozone would result in nearly 2 million extra cases of skin cancer.
The study was prepared as a background document for American negotiators at a conference in Vienna last month at which 43 nations debated whether international controls should be imposed on CFC production. The document has not been formally released but was made available on request.
Although American negotiators, led by Assistant Secretary of State James L. Malone, had hoped to persuade European nations to adopt an early ban on CFC use in aerosol sprays, which accounts for more than half the CFC produced, they settled for an agreement that merely commits the countries to cooperate in further study of the problem and to reconvene in 1987 for another attempt to limit production.
The agreement, which will be submitted to the Senate for ratification as a treaty, "is by no means the final solution, but it's a real step forward," Malone said yesterday at a briefing for representatives of industries that make and use CFC. Most were clearly pleased that the agreement stopped short of steps that would cut into their business.
Because the Soviet Union signed the agreement, which asks signatories to make public their CFC production figures, scientists hope to obtain an important new piece of information in calculating the threat to the ozone. Until now, Soviet CFC production has been estimated or not counted.
Deputy Assistant Secretary of State Richard E. Benedick, another of the negotiators, said the State Department concluded from existing evidence that the threat to the ozone is real. "The scientific evidence does point to some potential danger," he said, but he added that there is still time to act before the ozone depletion becomes significant.