Diagnosing The Risks

Trucking companies
Dangerous chemicals are most vulnerable to interception while they are being transported. Today 2.5 million Americans have commercial driver's licenses to carry fuels and other hazardous materials. Truckers must pass two tests: the federally mandated 30-question multiple-choice test (states can add more questions) to obtain a commercial vehicle license and a separate test on the procedures for safely handling hazardous substances. After the arrest of about 20 people suspected of fraudulently obtaining haz-mat licenses, chemical companies tightened their transport policies, assigning two drivers to every vehicle and using satellite tracking systems to monitor haulers from pickup to drop-off.

Food
Salmonella
As Oregon's Rajneeshee cult demonstrated in 1984, it is not difficult to set off a wave of food poisonings. Indeed, gastroenteritis caused by natural contamination and careless food handling afflicts millions and results in 5,000 deaths each year. The Rajneeshees considered a number of different viruses and bacteria, including those that cause hepatitis and typhus, but decided for their purposes (disrupting the outcome of a local election) on a strain of salmonella that would be debilitating but not fatal. Salmonella poisonings tend to be localized. With proper hygiene, the bacterium is not particularly contagious.

E. coli
An even easier bug to obtain is the familiar intestinal parasite E. coli. Naturally occurring outbreaks of E. coli, typically the result of fecal contamination in anything from hamburgers to swimming pools, sicken hundreds of thousands of Americans each year. In New York City this spring, a man was arrested after he was spotted spraying what turned out to be feces-laden water over the contents of a midtown salad bar (fortunately, no one got sick). A far more virulent strain of the bacterium called O157:H7 is sometimes fatal, but identifying and isolating the right strain is beyond the technical capabilities of most terrorists.

Foot-and-mouth disease
A terrorist attack aimed at crops and livestock would be less dramatic but might cause more disruption in the long run. Such attempts are not unheard of. In World War II, Britain accused Germany of dropping small cardboard bombs filled with beetle pests on English potato fields, and in the 1980s Tamil militants threatened to target Sri Lankan tea and rubber plantations with plant pathogens.

Perhaps the most worrisome threat to U.S. agriculture is foot-and-mouth disease, which can spread with astonishing speed in sheep, cattle and swine. Not seen in this country since 1929, the disease is harmless to humans but renders farm animals economically worthless. The U.S. could be forced to destroy much of its own livestock, as Great Britain had to do earlier this year.

Explosives
Car, truck and backpack bombs
Exotic weapons get a lot of attention, but conventional explosives and suicide bombers in pizza parlors, discotheques and shopping malls can spread terror with stunning effectiveness. Fertilizer bombs like the one that destroyed the Alfred P. Murrah Federal Building in Oklahoma City, Okla., in 1995 could wreak havoc with bridges, tunnels and buildings. Nuclear-power and chemical-manufacturing plants make even more horrifying targets. The 1984 leak at the Union Carbide plant in Bhopal, India, may have killed 3,000. Estimates of the final death toll from the 1986 explosion in the Chernobyl nuclear plant run as high as 30,000.

Nuclear weapons
The ultimate nightmare would be terrorists in the U.S. wielding nuclear weapons. For this reason, the ability to create--or worse, steal or buy--weapons-grade plutonium has long been an issue of great concern and international intrigue. Fortunately, the practical difficulties in acquiring precisely the right materials, not to mention the engineering know-how to jerry-build a nuclear device successfully, make this type of threat highly unlikely.

For more information, go to the TIME.COM and ON magazine guide to life in the age of terrorism: time.com/unhysterical