Bestselling author Amy Stewart (Copyright Delightful Eye Photography) Bestselling author Amy Stewart (copyright Delightful Eye Photography)

Reports that someone may have sent ricin-laced letters to President Obama and New York Mayor Michael Bloomberg left us wondering just how dangerous ricin really is.

In Book World, we turn to Amy Stewart with our poison- and death-threat-related questions.  She’s the author of six books, including “Wicked Plants: The Weed That Killed Lincoln’s Mother and Other Botanical Atrocities.”

Stewart says that ricin, which is found in castor beans, is nothing to take lightly.

“Ricin is one of the most deadly plant poisons in the world,” she writes in an e-mail from New York. “If the dose is strong enough, it’s a nasty way to go: Ricin prevents protein synthesis, which basically causes extremely unpleasant gastrointestinal distress followed by catastrophic organ failure.”

Unlike the radioactive polonium used to assassinate Alexander Litvinenko in 2006, ricin is easy to come by. “People grow castor beans in their gardens, and I see it planted in parks and landscapes all the time,” Stewart says. “It was the most spectacular specimen plant in the median strips in downtown Chicago when I was there a few years ago.”

But there’s good news, too. As a method of assassination, ricin poisoning is “actually surprisingly difficult.” Its taste is reportedly bitter, so a would-be killer couldn’t “slip it in the soup.”

“The thing to remember about ricin is that it is not easily made into an airborne spray that someone can just inhale,” Stewart says. “These ricin-laced letters would only pose a threat if someone actually ate the powder or inhaled it, but it’s not floating around in the air.”

"Wicked Plants: “Wicked Plants: The Weed That Killed Lincoln’s Mother & Other Botanical Atrocities” (Algonquin, 2009).

“The most famous victim is Georgi Markov, a Bulgarian dissident who was working for the BBC when he was assassinated” in 1978, according to Stewart. “A ricin pellet was injected into his leg, and they didn’t find it until the autopsy.”

For Stewart, who has been writing for years about “wicked” elements in the national world, there’s nothing unusually alarming about ricin.

“Castor beans are getting a lot of attention right now because of these high-profile cases, but really, the plant kingdom quietly goes about the business of manufacturing poisons all day, every day,” she says. “It’s a fairly routine part of what plants do.”