Ever since the anthrax and terrorist attacks of Sept. 11, 2001, the poison ricin has at times been lumped in with other bioterrorism agents because it comes from a relatively common plant and seems easy to make.
But the reality is that ricin has created far more scares than victims and is more a targeted poison than something to attack lots of people.
On Tuesday, an envelope addressed to Sen. Roger Wicker, R-Miss., tested positive for ricin after being received at a mail processing plant in suburban Maryland. In 2004, ricin was discovered in the sorting area of a mail room in a Senate office building.
Ricin is derived from the castor plant that makes castor oil. What makes it scary is that there is no antidote and it is at its deadliest when inhaled. It is not contagious.
Still, a draft of a 2010 Homeland Security Department handbook lists only one person killed by ricin. And that was a political assassination, in 1978, of a Bulgarian dissident who was injected — via specialized secret-agent style umbrella— with a ricin pellet.
People have been poisoned with ricin after eating castor beans, but it is not as well absorbed through the digestive track as it is when it is injected or inhaled, according to the Centers for Disease Control and Prevention.
The CDC categorizes ricin as a "Class B" threat, which is the agency's second-highest threat level. It ranks behind anthrax, botulism, plague, smallpox, tularemia and viral hemorrhagic fevers.
It can be aerosolized, released into the air and inhaled. The Homeland Security handbook says the amount of ricin that fits on the head of a pin is enough to kill an adult if properly prepared.
Of all the biological and chemical terror agents, "it is one of the least significant; it is a poison," said University of Maryland bioterrorism expert Milt Leitenberg.
Leitenberg said he was hard pressed to remember any case when an initial chemical test that showed the presence of ricin actually turned out to be ricin. Nearly every time it is a false alarm.
The list of ricin terror acts in the Homeland Security handbook includes several people who obtained or made ricin. And even that isn't as easy as online handbooks say it is, Leitenberg said.
"Ricin is best suited for small-scale attacks rather than mass-casualty scenarios," the Homeland Security handbook said. It says the best "route of exposure" is injection into the bloodstream, like in the Bulgarian case.
The Homeland Security handbook also says inhaling ricin is more dangerous than eating it, but "formulating ricin powder to produce the necessary size to be efficiently disseminated via aerosol requires technical skill."
Ricin powder, the handbook says, "could also be delivered to indoor targets via letters or packages."
If a person is exposed to ricin, his or her clothing should be removed and the person should be washed vigorously with soap and water and get medical attention, the Homeland Security handbook says.