When the homeland security alert level was recently raised to orange (high risk) from yellow (elevated risk), the announcement was accompanied by advice to run out and buy some plastic sheeting and duct tape. Sure enough, many did just that. Yet nobody bothered to ask what terrorist weapons could possibly be blocked by duct tape. What is it, exactly, that all those duct tape speculators thought they were protecting themselves against? It has been reported that a major reason for raising the alert level to high was that a captured terrorist claimed the United States was about to be hit with a "dirty bomb." A dirty bomb is a hypothetical weapon -- an ordinary bomb with radioactive material attached. The conventional bomb is what kills people. The radioactivity the bomb might spread (probably through cesium-137) is supposed to scare people in an area of about five city blocks by elevating the risk of cancer. Cancer is not something that could be avoided by sealing yourself off in an air-tight room. You would suffocate in a few hours. Unknown things are always the most frightening, and that includes "bioterrorism." Most people think of bioterrorism as infectious germs, but the recent scare talk has been about things that have to be inhaled, ingested or injected -- anthrax, botulinum toxin, ricin and aflatoxin. There are at least three interest groups with powerful incentives to keep the American public in a state of high anxiety about bioterrorism, even though that clearly paralyzes the economy. One such group is the Homeland Security agency. If you set up an agency to warn us when terrorists are about to strike, those working for the agency have a strong incentive to tell us the risks are always elevated or high. To lower the alert level to green (low) or even blue (guarded) would tell terrorists the coast is clear and also make the Homeland Security crew look foolish if terrorists attacked. To raise the alert to red (severe) would cause panic and make Homeland Security look even more foolish if nothing happened. So, there will always be only two alert levels -- orange and yellow -- and narrowing that list to zero would be a big improvement. A second interest group is the profitable nonprofit bioterrorism research industry, which lives off federal grants. Nearly four years ago, on March 16, 1999, science writer Daniel Greenberg warned in The Washington Post of a "whiff of hysteria-fanning and budget opportunism in the scary scenarios of the saviors who have stepped forward against the menace of bioterrorism." A third interest group consists of officials from the Defense and State departments, because hyping Iraq's "unaccounted for" biological weapons is supposed to create a possible link with terrorism and thus generate more enthusiasm for invasion. In his famed address to the United Nations, Secretary of State Colin Powell remarked that "we know from Iraq's past admissions that it has successfully weaponized not only anthrax but also other biological agents, including botulinum toxin, aflatoxin and ricin." He added that "the Iraqi regime has also developed ways to disburse lethal biological agents widely and discriminately into the water supply, into the air." In 1995, Powell explained, an Iraqi officer had told inspectors that Iraq "intended" to be able to spray anthrax from an unmanned aerial vehicle which, according to Powell, would be "an ideal method for launching a terrorist attack using biological weapons." The feasibility of such a terrorist attack depends on both the agents and the method of disbursing such agents into the air or, even less likely, into our chlorinated water supply. Iraq's hypothetical unmanned aircraft, for example, sounds difficult to smuggle into the United States and easy to shoot down. Consider the four agents mentioned by Powell -- ricin, aflatoxin, botulinum toxin and anthrax. Sen. Bill Frist, R-Tenn., wrote a useful book about bioterrorism, When Every Moment Counts, which does not even bother to mention ricin or aflatoxin. Ricin, a poison made from the castor bean, was considered an extremely unlikely terrorist weapon until a small amount of it was recently found in a London flat. Attorney General Ashcroft then said, "The recent arrests in London where chemical -- ricin -- was discovered ... demonstrate Al Qaeda's interest in carrying out chemical, biological and radiological attacks." But even if the link with Al Qaeda was proven, it demonstrates nothing about Al Qaeda's chemical or radiological capabilities. Ricin's only claim to fame as a terrorist weapon is that it was used to assassinate Bulgarian dissident Georgi Markov in London in 1978, using a special umbrella to implant a pellet of ricin in his leg. Deputy Defense Secretary Paul Wolfowitz says Iraq has enough ricin "to kill more than 1 million people." If a million people could be persuaded to stand in line to be injected, that might be true. Aflatoxin is a naturally occurring byproduct of mold, common in things like peanuts and corn. Its only terrorist use was in Graham Greene's 1978 novel, The Human Factor, where spiking an agent's whisky with aflatoxin caused liver cancer, which was blamed on the booze. In big doses it could cause liver cancer, but that is no reason to buy duct tape. Botulinum toxin is best known as "botox" -- a treatment for wrinkles. In theory, however, it could be deadly serious. As Frist points out, "There has not been a successful aerosol release of botulism toxin" and it "can't survive standard water treatment." The most plausible terrorist risk might be contaminating uncooked food and beverages, but past efforts to contaminate food have resulted only in illness. We have all become aware of anthrax, due to letter bombs that killed five. Yet Wolfowitz says Iraq may have enough anthrax "to kill hundreds of millions." Frist cites a 1970 study that estimated that if someone could somehow figure out how to spray anthrax over a city of 5 million, and if nobody noticed that for six days, then it might kill 100,000. To kill "hundreds of millions" with anthrax someone would have to: (1) persuade hundreds of millions to queue up to inhale the stuff, and (2) prohibit the resulting victims from taking antibiotics. Duct tape might be best used on Wolfowitz's mouth. As the national alert level bounces from yellow to orange and back again, and as we get more advice about buying duct tape and the like, this nonsense imposes some very real costs and risks. Endless efforts to keep Americans in a constant state of near-panic may help the sales of duct tape, but they are sure to discourage long-term planning by households or businesses. And hearing government officials cry "Wolf!" too often, particularly when it comes to hypothetical exotic weapons from distant lands, could easily make us insufficiently alert to far more likely dangers from terrorists using the same weapons here they use in Israel -- old-fashioned bullets and bombs.