Nuclear physics. Proton guns set their sights on taming radioactive wastes.

the most deadly compounds on Earth. Spike a rat’s water with 10 parts per billion—the equivalent of 7 teaspoons of dioxin dissolved in an Olympic-sized swimming pool—and there’s a 50/50 chance that the rat will die of liver cancer. Yet even tinier concentrations of dioxins fed to rats inhibit tumors. The seemingly paradoxical findings have some scientists suggesting what would have been unthinkable not long ago: testing modified dioxins as an anticancer agent in humans. Dioxin is a poster chemical of a bold campaign: to rehabilitate the old saw that poisons or radioactivity at low doses are good for you. The concept, known as hormesis, has been kicking around for decades but until recently had been considered a marginal effect tainted by an unfortunate association with homeopathy. The improbable return of hormesis from the scientific wilderness, however, has riven the toxicology community. A flurry of new findings and a reexamination of old ones have thrust hormesis into the limelight. Many drugs, vitamins, and essential minerals exhibit hormesis, as does alcohol: Moderate drinking lowers risk of heart disease, whereas higher levels are associated with higher risks of heart and liver disease. Calorie restriction, the sole indisputable means of extending an animal’s life span, may also be a form of hormesis, proponents say: The lack of calories stresses an organism, firing up responses such as DNA repair enzymes and apoptosis, or programmed cell death, which protect the body from environmental insults. And low doses of many chemical toxins, from cadmium to pesticides to dioxin, appear to have paradoxical and possibly beneficial effects on organisms. The heightened scientific scrutiny has generated juicy headlines: “Whatever doesn’t kill you might make you stronger,” begins an article in the September issue of Scientific American. “A little poison can be good for you,” declares a recent issue of Fortune. Hormesis is alluring because it challenges the conventional wisdom that toxicants and radiation punish the body at even the smallest of doses. If hormesis is as pervasive as its backers suggest, it could mean that regulations for many chemicals, from arsenic in drinking water to polychlorinated biphenyls at Superfund sites, are too stringent. “It would fundamentally change the whole riskassessment paradigm,” says Edward Calabrese, a toxicologist at the University of