Authorities search the studio of man who sent the 2013 ricin letters.Rogelio V. Solis / AP

Once again, someone appears to have sent envelopes stuffed with ricin to the government. The tests need to be confirmed, but two suspicious letters to the Pentagon were caught in an off-site mail screening. No one was exposed. The same person is also reported to have sent letters to Senator Ted Cruz and to the White House, though the contents of those have not been confirmed to contain ricin.

Ricin is a deadly toxin extracted from castor beans, and the directions for making it are no more than a Google search away. The process takes only a few days, and it requires equipment no more complicated than a coffee filter and chemicals you can buy in a hardware store. “It can be made in your house very easily,” says Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security.

In fact, it’s so easy that ricin mailers have not, historically, been a very competent bunch.

In 2003, two envelopes with vials of ricin were found addressed to the White House and to a Senate office. The potency of the ricin was too low to be a health risk. A decade later, three letters containing ricin were found addressed to Senator Roger Wicker, President Barack Obama, and a Mississippi judge. (The mailer turned out to be a tae kwon do instructor trying to frame an Elvis impersonator, with whom he had an online feud that began over a Mensa membership.) Weeks later, in May 2013, three more letters were found addressed to Obama, New York City Mayor Michael Bloomberg, and Bloomberg’s gun-control-advocacy group. (The mailer this time was an actress trying to frame her estranged husband.)

None of these instances resulted in anyone getting sick from the toxin. But the ricin senders in the 2013 cases were sentenced to 25 and 18 years in prison.

It’s not that ricin cannot be deadly effective. If pure enough when injected, a deadly dose of ricin is no bigger than a few grains of salt. The U.S. military considered coating bullets with the toxin during World War I. In 1978, infamously, a Bulgarian journalist was assassinated by a man who used an umbrella rigged to inject a pellet straight into his victim’s leg. Ricin can cause nausea, vomiting, or respiratory failure depending on the route of exposure. It is a fairly slow-acting poison, taking 36 to 72 hours to kill. There is no antidote.

But castor beans—which are also used to make the laxative castor oil—remain easy to buy because ricin just isn’t that good of a bioweapon. “It’s more a poisoner’s tool than a weapon of mass destruction. It doesn’t disperse or spread from person to person,” Adalja says.

If injecting ricin directly into a victim is quite effective, sending it by mail is not. Kitchen-lab operations are unlikely to make especially pure ricin. To be accidentally inhaled by the person opening mail, the ricin also needs to be a fine powder that can easily aerosolize, which is not a given. And, of course, mail to the White House is also screened off-site, far from any powerful government officials.

U.S. counterterrorism officials have warned in the past of al-Qaeda’s interest in ricin, but so far, the ease of making ricin has made it the toxin of choice for people with more motive than competence.

Adalja contrasted it to anthrax, which is also found in nature and whose spores also form a white powder that can fill an envelope. “If you go digging up dirt in South Dakota looking for anthrax spores and culture it and cultivate it, it’s going to take some skill level,” he says. “With ricin, you can go buy castor beans.” It’s maybe even too easy.

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