WASHINGTON — Ricin is one of the deadliest poisons and among the easiest to manufacture, but the toxin has generally been used as an instrument of murder and intrigue rather than as a weapon of war and terrorism, experts say.
The reasons are practical: Contaminating masses of people with ricin could be difficult. It does not reproduce, like bacteria, and the illness it causes cannot be passed from a victim to another person. In addition, symptoms take hours to develop, making ricin useless for inflicting quick death.
"It didn't make a good mass-casualty weapon," said David R. Franz, former commander of the U.S. Army Medical Research Institute of Infectious Diseases at Ft. Detrick, Md., which conducts biodefense research.
"It's been used in what are considered crimes, not terrorist offenses," he said.
Last fall, someone claiming to be a disgruntled trucker tried to mail a container of ricin to the U.S. Department of Transportation.
Last year, police in London raided a suspected ricin lab run by a group linked to Al Qaeda. And police in Paris found traces of ricin in a train station locker linked to a militant Islamist group.
Ricin is produced from the castor bean plant, an ornamental woody herb prized by gardeners. The plant is legal to grow, and the oil from castor beans has been used for years in such diverse products as laxatives for humans and lubricants for high-performance engines.
"The seeds are kind of pretty, and people make necklaces from them," said Dan L. Brown, a nutritional toxicologist at Cornell University. "But it's about as poisonous as you can get."
The ricin toxin is extracted from crushed castor beans, or from the waste "mash" left over after producing castor oil.
Making the poison is simple enough -- instructions are on the Internet -- that an amateur chemist can follow the process.
Toxicologists classify ricin as a cell toxin. Breathed in, swallowed or injected, ricin kills human cells by shutting down their ability to produce proteins, which they need to function. For example, people who inhale ricin develop difficulty breathing within a few hours. Their condition can deteriorate into respiratory failure and death within three days.
"Everything starts to shut down," said Marilynn Etzler, a UC Davis biochemist who has performed experiments with ricin. "It is a very dangerous thing to work with."
Depending on the concentration of the dose and the method of ingestion, a small amount of ricin can kill an adult. A pinhead-sized dose is sufficient if injected, according to the federal Centers for Disease Control and Prevention. Greater amounts are needed to kill by inhalation or ingestion.
There is no antidote for ricin poisoning, but the symptoms are treatable.
Adults who ingest a small amount of ricin by chewing a few castor bean seeds often survive.
Ricin has been used in experimental cancer treatments with mixed results, but otherwise has no medicinal purpose.
The most notorious case involving ricin poisoning was in 1978. Georgi Markov, a Bulgarian dissident working in London, was stabbed in the leg by an unknown assailant wielding what appeared to be an umbrella. Markov died a few days later after developing symptoms of ricin poisoning. No one has been arrested, but authorities suspect agents of former Communist bloc countries.
In the United States, antigovernment groups have experimented with the poison.
In 1995, four members of a Minnesota tax protest group were convicted in a plot to kill a federal marshal. They were going to apply ricin to the door handles of the marshal's vehicle.
In 1993, Canadian authorities confiscated a container of ricin from Thomas Lavy, an American white supremacist who was trying to enter Canada from Alaska. The Canadians allowed Lavy to go free, but he was arrested by the FBI two years later. Agents discovered castor beans in his Arkansas cabin. Lavy committed suicide in jail.
Last month, the FBI offered a $100,000 reward for information in a ricin case involving the Department of Transportation. A letter writer identified only as "Fallen Angel," who claimed to be a trucking company owner, sent the department a threatening letter calling for the repeal of new rules that limit truckers' hours at the wheel. A metal vial containing ricin was included with the letter, which was intercepted Oct. 15 by postal workers in Greenville, S.C.
"I have easy access to castor pulp," the writer warned. "If my demand is dismissed, I'm capable of making ricin." If the rules remain unchanged, he added, "I will start dumping." No link has been established between that case and the Senate incident.
The investigation of the cases involving the Senate and the White House may be more difficult.
More than two years after letters containing deadly anthrax spores coursed through the nation's mail system, that case remains unsolved. Five people were killed; a public shaken by the Sept. 11, 2001, terrorist attacks was traumatized. One of the letters, which were mailed to legislators and news media outlets, went to the office of Sen. Tom Daschle (D-S.D.), then Senate majority leader.
For much of 2002 and 2003, the government appeared to be zeroing in on a virologist who had worked at an Army lab. The researcher, Steven J. Hatfill, was described by U.S. Atty. Gen. John Ashcroft as a "person of interest" in the case. Hatfill has sued the government, asserting his innocence and charging that he is being made into a scapegoat.
The anthrax investigation remains "intensely active," said FBI spokeswoman Debra Weierman, with 28 FBI agents and a dozen postal inspectors working on the case full time.
Times staff writer Richard B. Schmitt contributed to this report.