There have been a few incidents of mail purporting to contain the chemical poison ricin. Ricin is made from castor beans, a plant that is plentiful in many areas of the world, including the United States. Castor beans are used to make castor oil and other beneficial products used for many purposes. In fact, castor oil is often used in the manufacture of paper, including paper used as envelopes. Trace amounts of castor are present in many common items. The process for making ricin from castor beans is rather difficult and quite dangerous. Common first responder field kits have been known to show positive test results for the poison ricin in substances containing harmless amounts of castor bean pulp or derivatives. A positive field test for ricin may result from castor bean products, even if there is no refined ricin. To be dangerous, ricin must be injected, inhaled, or ingested.

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