Only hardy spore-forming bacteria like Bacillus anthracis can live amid the tough conditions–no food, no water–in the mail. Clostridium botulinum, the bacterium that produces deadly botulism toxin, also forms spores, but they’re anaerobic. That is, oxygen in air kills them. Bacteria that do not sporulate–and viruses that live only in living cells–cannot survive without food and water. Yes, a terrorist could mail E. coli O157-tainted hamburger, or a vial of Ebola-laced blood, but neither would be the surreptitious killer that anthrax is. Chemical weapons? Most are highly volatile gases, which would dissipate almost before the envelope was sealed. Liquids like the nerve agents sarin and VX would evaporate before hurting anyone but the mailer. Explosives have a deadly record–the Unabomber killed three and injured two–but don’t arrive in envelopes.
The latest worry is that anthrax spores from one envelope can escape and contaminate others; a recipient would not even find a telltale powder. Yes, anthrax spores can escape through the 10-micron pores of a typical envelope, especially when squashed by postal sorting machines. What remains unknown is whether (and if so, how many) spores can cling to the outside of an envelope that passed through the same machines. Until that is determined, anyone concerned that his mail suffered this secondary contamination can invest in a fitted N-95 mask. The $1.35 mask filters out particles down to 0.3 micron; the deadliest clumps of anthrax spores are 1 to 5 microns across. But don’t bother microwaving mail. Microwaves heat by exciting water molecules, of which there are precious few in the fluffy samples of anthrax that pose the greatest danger.
The Postal Service is investigating ways to kill the spores before they reach mailboxes. The most promising technology is irradiation, which rips apart an organism’s DNA. In electron-beam radiation, a stream of electrons bombards a target, typically penetrating to about half the depth of a hamburger, says microbiologist Michael Doyle of the University of Georgia. X-rays go even further. Although irradiation would not harm paper mail, it could damage electronic devices, film and some medicines. The Postal Service is already trucking mail from the Brentwood sorting center, which handled the anthrax-laced letter to Sen. Tom Daschle and where two workers died of inhalation anthrax, to irradiation facilities in Ohio. Over the next few months, it will buy irradiation machinery for “targeted areas” like Washington and New York postal facilities, says spokesman Greg Frey. Extending the screening might not be practical, though. To treat mail from the nation’s 38,000 post offices would require 250 new distribution centers. The irradiation machines alone would cost an estimated $2.5 billion. “This new technology won’t be cheap,” Postmaster General John Potter said last week, “but we are committed to spending what it takes to make the mail safe.”
FIRST STEPS: Start by having the USPS irradiate suspect mail. Follow guidelines on identifying suspicious mail. For an extra layer of security, wear a mask and gloves while going through the day’s deliveries.
