Reuters (via Malkin):

An FBI-led task force is trying find out how the deadly poison ricin wound up in a student dormitory at the University of Texas, a campus police spokeswoman said on Saturday.
A chunky white powder, less than the amount that would fill a plastic sandwich bag, was found on Thursday night and preliminary tests on Friday showed it to be ricin, a poison made from castor beans, spokeswoman Rhonda Weldon said. "This is not associated with any threats against the campus" in Austin, Texas, Weldon said. A spokesman for the FBI San Antonio Joint Terrorism Task Force was not immediately available to comment.

Ricin is extracted from castor beans and even small amounts of it can kill if inhaled or injected, according to the U.S. Centers for Disease Control and Prevention web site. Toxicologists say it can easily be made in an ordinary kitchen. In 2005, an al Qaeda-trained Algerian man, Kamel Bourgass, was convicted in a plot to spread ricin throughout streets in Great Britain.

Humid weather apparently caused the ricin powder to clump together, reducing the risk to those exposed, according to CNN.

No known antidote exists for ricin.