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ANAHEIM, Calif. - There's good news and bad about compounds called nitrosamines that have caused cancer in more than 40 species of laboratory animals and may cause cancer in humans, an Oregon State University scientist said today (Monday, March 22) at the annual meeting of the American Chemical Society.

"The takeaway messages are that there's been very good attention paid in the United States to nitrosamines in foods such as bacon and beer and there have been reductions, but less attention has been paid to nitrosamines in other sources such as certain industrial settings and cosmetics," said Oregon State food scientist Richard Scanlan.

Scanlan, who has studied nitrosamines for more than 30 years - including how they form and how to measure and reduce their levels - delivered the opening overview session of a day-long American Chemical Society symposium on the compounds.

Nitrosamines were discovered more than 100 years ago but did not draw heavy scrutiny until 1956 when they were found to cause cancer in laboratory test animals.

The Oregon State researcher explained that Americans are exposed to the compounds via diet, smoking, cosmetics and, with some workers, occupational exposure such as breathing aerosols formed during the manufacture of rubber and during metal cutting.

"It's been known since the 1970s that they were in cured meats such as fried bacon, and they were found in beer in 1979," said Scanlan. "There's been a lot of research and a dramatic reduction of their levels in these kind of foods since then. For instance, today there are only 1 to 2 percent of the nitrosamines in beer that there were 20 years ago."

In the United States today, using tobacco and working in certain occupational settings probably present a higher risk of exposure to the cancer-causing forms of nitrosamines than most diets, Scanlan pointed out.

"You could eat a quarter pound of bacon a day and drink a six pack of beer and the exposure would be less than smoking a couple of packs of even low-tar, filtered cigarettes," he said, though he added that "these kinds of cross-comparisons are very difficult to make."

The average daily exposure of Americans to carcinogenic types of nitrosamines from foods is thought to have dropped from about 1 microgram a day to perhaps a tenth of that, said Scanlan.

"Most people who work in the field of nitrosamine research seem to feel that this (the current estimated average daily exposure from foods) is not a hazardous level for humans," he said. "But no one can say for sure. No threshold level for nitrosamines has been established for human cancer. No one knows at what dose they pose a problem.

"What researchers do know is that about 90 percent of all nitrosamine compounds tested in experimental animals have been shown to cause cancer," he added. "That includes research with more than 40 species from mice and rats to hamsters, monkeys and even snakes. That's about the strongest indirect evidence one could amass that they cause cancer in humans if the dose is high enough."

At the symposium, the OSU scientist urged researchers to pay less attention to average exposure rates and more attention to maximum daily exposure rates for carcinogenic nitrosamines.

"If anybody is affected," he argued, "it is probably people getting the high daily exposure, such as people who smoke a couple of packs of cigarettes per day."