*3.2. Inhalation Toxicity*

No data are available for human ricin uptake by inhalation. In non-human primates, LD50 has been estimated to be 5 to 15 μg/kg depending on aerosol particle size. Inhalation of particles that are able to penetrate deeply into the lungs (1 to 5 μm diameter) display much more toxicity than larger particles [72,80]. Inhalation of ricin causes slow onset of respiratory distress (di fficulty breathing), coughing, fever, pulmonary lesions, and edema. Intoxicated animals develop fibrinopurulent necrotizing pneumonia accompanied by necrotizing lymphadenitis, typically after a dose-dependent delay of 8 to 24 h. Death occurs as a result of respiratory failure due to massive alveolar fluid accumulation. The liver, kidney, and small intestines appear congested, although little histologic changes have been shown [72,80,81].
