According to Wikipedia, ricin is a highly toxic poison that can kill in very small amounts:
Ricin/ˈraɪsɪn/, from the castor oil plantRicinus communis, is a highly toxic, naturally occurring carbohydrate-binding protein of the type known as lectins. A dose the size of a few grains of table salt can kill an adult human. The median lethal dose (LD50) of ricin is around 22 micrograms per kilogram (1.78 mg for an average adult, around 1⁄228 of a standard aspirin tablet/0.4 g gross) in humans if exposure is from injection or inhalation. Oral exposure to ricin is far less toxic and a lethal dose can be up to 20–30 milligrams per kilogram.
I’m no chemist, biologist, nor doctor, but it would seem to me that if ricin is deadly in such small amounts, then this letter should have dropped an elephant.
Then there is this curious fact in the ABC News story about the letters themselves.
The letters never made it to Obama or Bloomberg and today the U.S. Postal Service said none of the letters posed a health risk. The letters — all reportedly with identical text — are postmarked May 20 from Shreveport, La.
If the letters posed no health risk, then they did not contain actual ricin. There is no other real conclusion to draw from this.
Only one substance would test positive for low levels of ricin, but wouldn’t be a health threat, and that’s the castor bean mash used. Again, from Wikipedia.
The seeds can be crushed in an oil press to extract castor oil. This leaves behind the spent crushed seeds, called variously the ‘cake’, ‘oil cake’ and ‘press cake’. While the oil cake from coconut, peanuts and sometimes cotton seeds can be used either as cattle feed and/or fertilizer, the toxic nature of castor precludes them from being used as feed Accidental ingestion of Ricinus communis cake to be used as fertilizer has been reported to be responsible for fatal ricin poisoning in animals.
Putting all this together, it seems Mayor Bloomberg, MAIG, and President Obama were sent fertilizer.
The intent was to cause panic and fear, so this is still not a laughing matter, but it appears that the media is working mightily to turn an any possible anthill into Everest.