"More research needs to be done," says Mucci. "But the preliminary evidence is somewhat reassuring."
Other experts, including government scientists, contend that -- with definitive evidence lacking -- California should do what it can to reduce the risk. They emphasize that though acrylamide does exist in a wide variety of foods, its high levels in fries and chips lend special concern.
"We definitely believe acrylamide is a chemical to be concerned about," says George Alexeeff, deputy director for scientific affairs at the state Office of Environmental Health Hazard Assessment, the office that oversees implementation of Proposition 65. "Our general presumption is that unless there's some other evidence, we assume that if something causes cancer in animals, it causes cancer in humans."
The Environmental Protection Agency considers acrylamide potentially so dangerous that it has fixed the safe level for human consumption at almost zero, with a maximum permissible level in drinking water of 0.5 parts per billion.
By comparison, a 2.4-ounce serving of French fries, a small portion at McDonald's, contains about 401 parts per billion, a small, vending-machine-sized bag of potato chips 466 parts per billion.
According to published studies, the average American consumes 40 micrograms of acrylamide a day -- much of it in coffee, a cup of which has 7 parts per billion.
Swedish researchers discovered its presence in food almost by accident while testing workers exposed to acrylamide during railroad construction. When the scientists set up a control group, they were stunned to find high levels across the board.
"They got alarmed, brought it up to the World Health Organization and a series of meetings were convened fairly quickly to look at this issue," says Carl Winter, director of the FoodSafe Program at UC Davis, where he researches naturally occurring toxins in food.
From his viewpoint as a food toxicologist, such fear may not be warranted.
"It's the levels of exposure that determine the risks," he says. "We don't need to take a green light-red light approach to foods. If we eat foods in moderation, we can have very healthy diets."
When it comes to toxicology, the argument goes, the size of the dose makes the poison.
"Dose is the key," says Lois Swirsky Gold, senior scientist and director of the Carcinogenic Potency Project at UC Berkeley, who says that scientists don't yet know that the chemical is hazardous in the doses people get through their diet.
