Got Toxic Milk?

Stanford, Calif. - WHILE the anthrax scare at Washington post offices this year proved to be a false alarm, it was a reminder of how vulnerable Americans are to biological terrorism. In general, two threats are viewed as the most dangerous: anthrax, which is as durable as it is deadly, and smallpox, which is transmitted very easily and kills 30 percent of its victims.

But there is a third possibility that, while it seems far more mundane, could be just as deadly: terrorists spreading a toxin that causes botulism throughout the nation's milk supply.

Why milk? In addition to its symbolic value as a target -- a glass of milk is an icon of purity and healthfulness -- Americans drink more than 6 billion gallons of it a year. And because it is stored in large quantities at centralized processing plants and then shipped across country for rapid consumption, it is a uniquely valuable medium for a bioterrorist.

For the last year, a graduate student, Yifan Liu, and I have been studying how such an attack might play out, and here is the situation we consider most likely: a terrorist, using a 28-page manual called "Preparation of Botulism Toxin" that has been published on several jihadist Web sites and buying toxin from an overseas black-market laboratory, fills a one-gallon jug with a sludgy substance containing a few grams of botulin. He then sneaks onto a dairy farm and pours its contents into an unlocked milk tank, or he dumps it into the tank on a milk truck while the driver is eating breakfast at a truck stop.

This tainted milk is eventually piped into a raw-milk silo at a dairy-processing factory, where it is thoroughly mixed with other milk. Because milk continually flows in and out of silos, approximately 100,000 gallons of contaminated milk go through the silo before it is emptied and cleaned (the factories are required to do this only every 72 hours). While the majority of the toxin is rendered harmless by heat pasteurization, some will survive. These 100,000 gallons of milk are put in cartons and trucked to distributors and retailers, and they eventually wind up in refrigerators across the country, where they are consumed by hundreds of thousands of unsuspecting people.

It might seem hard to believe that just a few grams of toxin, much of it inactivated by pasteurization, could harm so many people. But that, in the eye of the terrorists, is the beauty of botulism: just one one-millionth of a gram may be enough to poison and eventually kill an adult. It is likely that more than half the people who drink the contaminated milk would succumb.