EFFECT OF AQUEOUS CHLORINE AND OXYCHLORINE COMPOUNDS ON CRYPTOSPORIDIUM-PARVUM OOCYSTS

Aqueous chlorine, chlorine dioxide, sodium thiosulfate, chlorite, and chlorate were evaluated for their effect on Cryptosporidium parvum ooc ysts under drinking water disinfection conditions. Experiments were co nducted in 40 mL of oxidant demand-free 0.05 M phosphate buffer at pH 8.0 and 22 +/- 1 degrees C. Animal infectivity using neonatal CD-1 mic e was used to estimate the viability of the oocysts after disinfection . Chlorine dioxide was an effective disinfectant. Aqueous chlorine, so dium thiosulfate, chlorite, chlorate, and the reaction byproducts of c hlorite or chlorate when reduced with sodium thiosulfate had no detect able effect on Cryptosporidium oocysts. These results suggest that chl orine dioxide is the active agent responsible for inactivation of Cryp tosporidium oocysts under typical conditions of chlorine dioxide appli cation for drinking water disinfection.