Ricin is a poison made from the waste left over from the processing of seeds of the castor bean plant, Ricinus communis. Castor beans are processed throughout the world to make castor oil and ricin is part of the waste "mash" produced when castor oil is made. Ricin can be in the form of a powder, a mist, or a pellet, or it can be dissolved in water or weak acid. Exposure to ricin would require a deliberate act to make the substance and introduce it into the systems of victims. Unintentional exposure to ricin is very unlikely.
The US Centers for Disease Control and Prevention (CDC) (www.cdc.gov) maintains a web page devoted exclusively to ricin (http://emergency.cdc.gov/agent/ricin/qa.asp) which includes excellent technical documents about the poison. Links are provided below to these documents, selected from the several dozen available, as useful for persons, including health care professionals, looking for a rapid, basic orientation to ricin.
Physicians and health care facilities should report suspected cases of exposure to sarin to their local county health department.