Effect of Aqueous Chlorine and Oxychlorine Compounds on <i>Cryptosporidium parvum </i>Oocysts

Abstract

Aqueous chlorine, chlorine dioxide, sodium thiosulfate, chlorite, and chlorate were evaluated for their effect on Cryptosporidium parvum oocysts under drinking water disinfection conditions. Experiments were conducted in 40 mL of oxidant demand-free 0.05 M phosphate buffer at pH 8.0 and 22 ± 1 °C. Animal infectivity using neonatal CD-1 mice was used to estimate the viability of the oocysts after disinfection. Chlorine dioxide was an effective disinfectant. Aqueous chlorine, sodium thiosulfate, chlorite, chlorate, and the reaction byproducts of chlorite or chlorate when reduced with sodium thiosulfate had no detectable effect on Cryptosporidium oocysts. These results suggest that chlorine dioxide is the active agent responsible for inactivation of Cryptosporidium oocysts under typical conditions of chlorine dioxide application for drinking water disinfection.