The inactivation kinetics of bacteriophage f2 were studied by using ozone under controlled laboratory conditions. The phage were rapidly inactivated during the first 5 s of the reaction by 5 and 7 logs at ozone concentrations of 0.09 and 0.8 mg/liter, respectively. During the next 10 min, the phage were further inactivated at a slower rate in both treatments. The [ 3 H]uridine-labeled f2 phage and its ribonucleic acid (RNA) were examined to elucidate the mechanism of ozone inactivation, utilizing adsorption to host bacteria, sucrose density gradient analysis, and electron microscopy. The specific adsorption of the phage was reduced by ozonation in the same pattern as plaque-forming unit reduction. RNA was released from the phage particles during ozonation, although it had reduced infectivity for spheroplasts. Electron microscopic examination showed that the phage coat was broken by ozonation into many protein subunit pieces and that the specific adsorption of the phage to host pili was inversely related to the extent of phage breakage. The RNA enclosed in the phage coat was inactivated less by ozonation than were whole phage, but inactivated more than naked RNA. These findings suggest that ozone breaks the protein capsid into subunits, liberating RNA and disrupting adsorption to the host pili, and that the RNA may be secondarily sheared by a reduction with and/or without the coat protein molecules, which have been modified by ozonation.

The effects of ozone and storage temperature on the survival of Giardia lamblia cysts, the cause of human giardiasis, and Giardia muris, a parasite of mice, were compared. The viabilities of the cysts were similar over a period of 25 days of storage in the range of -6" to 37°C; the optimum temperature for their long-term survival was determined to be about 5°C. Ozone was extremely effective for inactivating cysts of both Giardia species, with G. muris being consistently more resistant than G. lamblia at pH 7 and 5°C and 25°C.

Poliovirus 1 isolants were recovered from finished drinking water produced by a modern, well-operated water treatment plant. These waters contained free chlorine residuals in excess of 1 mg/liter. The chlorine inactivation of purified high-titer preparations of two such isolants was compared with the inactivation behavior of two stock strains of poliovirus 1, LSc and Mahoney. The surviving fraction of virus derived from the two natural isolants was shown to be orders of magnitude greater than that of the standard strains. These results raise the question whether indirect drinking water standards based on free chlorine residuals are adequate public health measures, or whether direct standards based on virus determinations might be necessary.

Giardia lamblia cysts were inactivated in water with ozone at pH 7.0 and 5 and 25 degrees C. The concentration-time products for 99% inactivation were 0.53 and 0.17 mg-min/liter at 5 and 25 degrees C, respectively. These products were significantly lower than those reported for chlorine.

The inactivation of HEp-2 cell-associated poliovirus (Sabin 1) and coxsackievirus A9 was investigated in three experimental systems, using ozone as a disinfectant. The cell-associated viral samples were adjusted to a turbidity of 5 nephelometric turbidity units. The cell-associated poliovirus and coxsackievirus samples demonstrated survival in a continuous-flow ozonation system at applied ozone dosages of 4.06 and 4.68 mg/liter, respectively, for 30 s. Unassociated viral controls were inactivated by the application of 0.081 mg of ozone per liter for 10 s. Ultrasonic treatment of cell-associated enteric viruses did not increase inactivation of the cell-associated viruses. The batch reactor with a declining ozone residual did not effect total inactivation of either cell-associated enteric virus. These cell-associated viruses were completely inactivated after exposure to ozone in a batch reactor using continuous ozonation. Inactivation of cell-associated poliovirus required a 2-min contact period with an applied ozone dosage of 6.82 mg/liter and a residual ozone concentration of 4.70 mg/liter, whereas the coxsackievirus was completely inactivated after a 5-min exposure to an applied ozone dosage of 4.81 mg/liter with an ozone residual of 2.18 mg/liter. These data indicate that viruses associated with cells or cell fragments are protected from inactivation by ozone concentrations that readily inactivate purified virus. The cell-associated viral samples used in this research contained particles that were 10 to 15 microns in size. Use of a filtration system before ozonation would remove these particles, thereby facilitating inactivation of any remaining viruses associated with cellular fragments.