Is exposure to a chemical that causes skin cancer less dangerous than exposure to a lung carcinogen?

The question has evoked an affirmative and controversial response from a panel of top Environmental Protection Agency managers. Determining that exposure to the skin carcinogen is less dangerous because it causes fewer deaths, the panel departed from a longstanding agency practice of weighing equally the risks of cancer-causing chemicals regardless of their health effect.

Although the panel was assessing the dangers of arsenic in an internal review last July, its recommendation to "discount" the risk of skin cancer caused by the chemical is believed to have far-reaching implications for regulation of the hundreds of other toxic substances that litter the environment.

The recommendation has split the scientific community inside and outside the agency, with opponents arguing that its approval could result in more lenient standards for chemicals that cause debilitating but nonfatal illnesses.

Victor Kimm, the EPA's deputy assistant administrator for pesticides and toxic substances and a panel member, said such regulatory distinctions would be "appropriate" to determine how best to allocate resources. For example, he said, the cleanup of a toxic waste site posing the risk of nonfatal cancers should be "less of an urgency and less herculean" than of a site discharging lethal carcinogens.

But Herman Gibb, an EPA epidemiologist who worked on the arsenic review, warned that rating carcinogens on the basis of fatality would shift the regulatory focus from prevention of disabling disease to death concerns.

"Just because you don't die of it doesn't mean the disease isn't a problem," said Gibb, citing relatively good survival rates for leukemia and certain cancers.

Despite its broad implications, the issue grew out of a narrow regulatory debate. The subject was arsenic -- an air, soil and water pollutant put into the environment by smelting operations, metal processing and pesticides.

The EPA regards arsenic inhalation as a cause of lung cancer. But the agency has long been divided over the danger of consuming the chemical in food and water. This has caused conflicts in the Superfund cleanup program, where arsenic contamination of ground water is considered a cancer risk.

Asked to resolve the conflict, the EPA's Risk Assessment Council ordered a study by 10 senior agency scientists. They reported last December that, based on studies in Taiwan, oral ingestion of arsenic causes skin cancer. They stressed such tumors are easily diagnosed and treated and are rarely fatal.

The council, composed of the agency's top scientific managers headed by Assistant EPA Administrator Jack Moore, reviewed the report and issued recommendations last July in a memorandum to EPA Administrator Lee M. Thomas.

"For purposes of consistency," Moore said, the agency should adopt a uniform risk assessment for orally consumed arsenic. Such assessments project the increased chances of getting cancer from a lifetime's exposure to a carcinogen.

But, noting that skin cancers are "more likely to be detected and successfully treated and less likely to lead to death" than the lung tumors caused by arsenic inhalation, Moore recommended that the risk assessment for orally ingested arsenic be discounted between 10- and 100-fold from its current level.

Critics argue that such discounting would result in relaxing controls of the pollutant because the agency gears its standards according to the extent of health risk.

"It represents very poor science and very poor public health policy," said Dr. Philip Landrigan, director of environmental and occupational medicine at the Mount Sinai School of Medicine in New York City. He noted that two of the three types of skin cancers caused by arsenic consumption often are fatal and that oral ingestion of the pollutant is known to cause other health problems, including lethal liver cancer, cardiovascular disease and a nervous system disorder.

Alexandra B. Smith, deputy administrator for the EPA's western region, wrote Moore a "confidential" memo expressing concern that such a "drastic change" in the risk estimate for arsenic would "severely undercut" the agency in getting the polluter of a Montana toxic waste site to relocate residents.

She wrote in August that the arsenic decision would affect five other sites in her region.

Moore, the EPA's chief of pesticides and toxic substances, failed to respond to repeated interview requests on this subject. Kimm, Moore's deputy, dismissed Smith's concerns, noting that remedial plans at most Superfund sites hinge on more than one chemical.

The concerns raised by Moore's recommendation go beyond the arsenic issue. Smith, in her memo, questioned whether it presaged revisions in risk estimates for other cancers, such as leukemia, that do not always result in death. Would the agency revise its assessments of other hazardous substances, such as lead, which cause neurological damage but are rarely fatal? Smith asked.

According to epidemiologist Gibb, discounting the arsenic risk would set a "bad precedent," requiring a review of "all other things the agency regulates that don't cause death."

Peter Preuss, director of the EPA's office of health and environmental assessment and a member of the Risk Assessment Council, said the implications of the arsenic review may be limited to arsenic.

"It's unlikely the agency would do this for other cancers," Preuss said.

Carcinogens are the only chemicals at stake in the debate because they present a risk at any level, he said. Other hazardous chemicals, which do not result in fatal diseases, can be regulated to a point below which there is no risk, he said.

Still, Preuss acknowledged, the review is a significant test of the "way in which the agency has historically done business," which is not to distinguish among carcinogens on the basis of severity of their health effects.

"The policy of the agency has been to take a conservative approach on these issues," he said. "If you move away from it, the problem is how far do you move."