1 Also present are ricinine, an alkaloid, and an irritant oil. 2  According to the 2007 edition of the Guinness Book of World Records, the castor oil plant is the most poisonous in the world, though its cousin abrin, found in the seeds of the jequirity plant, is arguably more lethal. One of the most toxic plants found in the Western hemisphere, all parts of the plant contain tropane alkaloids. 2  The active agents are atropine, hyoscine (scopolamine), and hyoscyamine, which have anticholinergic properties.