Toxin fate has become an important research topic due to frequent bioterrorism threats. Ricin is a toxin derived from castor beans. Ricin added to microbial communities may stress the community and/or be used as a carbon source. To understand ricin effects on microbial communities, two greenhouse experiments to measure ricin degradation were conducted. A long-term experiment was conducted using three soil types. Castor beans were blended with water and was added to soil, mixed and packed into a one-liter pot. Ten replicates of each soil were treated, and ten replicates were used as a control. Microbial respiration was measured for six months. Differences between soils and treatments were indicated for the first three weeks. An experiment to determine the effect of non-ricin components of castor bean was conducted. For two treatments, castor bean and autoclaved castor bean were individually blended with water; was added to soil, mixed and packed into one-liter pots. Each treatment (and control) was replicated five times. Microbial respiration was measured for four weeks. Respiration rates for the autoclaved castor were 65% higher than the castor treatment for 15 days, while the castor treatment was 100% higher than the control for 5 days. After day five, the average respiration rate for the control and castor treatment was 0.40 g CO₂ m^-2 hr^-1 and after 15 days, the average respiration rate for all treatments was 0.30 g CO₂ m^-2 hr^-1. Results indicate that soil type is significant with respect to microbial activity immediately following an exposure to ricin. The non-ricin components of castor beans increase microbial activity, while ricin has a negative effect.