The VRE of the test filters was calculated by analyzing the infectivity of viruses collected

on both control and experimental impingers for challenging and penetrating viruses from the

filter. The result is presented as an average of five 2-hr experimental runs for each filter

indicated as No. 1 and No. 2 in Table 3-1 (raw data are available in Appendix C). As shown, the

iodine-treated filter presented a significantly higher VRE than that of the untreated filter (p-value

< 0.05) at various environmental conditions. At HT/LRH, a significantly higher value of the

iodine-treated filter than that of the other conditions was observed, according to one-way

ANOVA (p-value < 0.05), due to increased release of 12 from the filter. Meanwhile, the

difference between RT/LRH and RT/MRH was not significant (p-value > 0.05), indicating that

the release of HOI into air due to the hydrolysis of 12 at increased RH is negligible.

Inactivation Mechanisms of the Iodine-Treated Biocidal Filter

 The effect of sublimation and dissolution of I2 was investigated by using the impingers

containing a virus suspension of known concentration either in the PBS or sodium thiosulfate

solution. As shown in Table 3-2, no surviving virus was detected in the experimental impinger

until > 104 PFU in the PBS was added to the impingers. As the virus concentration in the

impinger increased, the number of surviving viruses also increased. Meanwhile, the survival

fraction of viruses in the thiosulfate solution was much higher than that in the PBS. Most viruses

suspended in the thiosulfate solution survived in the experimental impinger due to quenching by

reaction with thiosulfate of the I2 released from the iodine-treated filter and/or 12 transferred to

viral aerosols. Hatch et al. (1980) proposed spontaneous dissociation of 2 from the

polyiodide-resin complex as one of three possible inactivation mechanisms of their iodinated

resin filter in water treatment. In another study (Marchin et al. 1983), acquisition of l2 by a cyst

during passage through an iodinated resin column was hypothesized. The authors observed that