Influence of environmental conditions on the attenuation of ricin toxin on surfaces

Ricin is a highly-toxic compound derived from castor plant beans. Several incidents involving contamination of residences and buildings due to ricin production or dissemination have occurred in recent years. The goal of this study was to determine whether ricin bioactivity could be attenuated in reasonable time via simple modifications of the indoor environment. Attenuation was assessed on six different materials as a function of temperature, relative humidity (RH), and contact time, using both a pure and crude preparation of the toxin. Ricin bioactivity was quantified via a cytotoxicity assay, and attenuation determined as the difference in ricin recovered from test and positive controls. The results showed that pure ricin could be attenuated successfully, while the crude ricin was generally more persistent and results more variable. We found no significant attenuation in crude ricin after two weeks at typical indoor environmental conditions, except on steel. Attenuation mostly improved with increasing temperature, but the effect of RH varied. For pure ricin, heat treatments at 40°C for 5 days or 50°C for 2–3 days achieved greater than 96% attenuation on steel. In contrast, appreciable recovery of the crude ricin preparation still occurred at 40°C after two weeks.