How do contact times get involved? Disinfectants often have several mechanisms of action that will be lethal to microbes at different rates. One of the fastest acting mechanisms is oxidation. A strong oxidizer, such as ozone, or a strongly oxidizing condition, such as concentrated hypochlorite or chlorine dioxide, will rapidly steal electrons from the microbial membrane resulting in the loss of its vital functions. Under milder oxidizing conditions, between 500 and 600 mV, bacterial inactivation will occur but only after much longer contact exposure. Trevor V. Suslow, Ph.D. U.C. Davis