Enhanced Inactivation of <i>Cryptosporidium parvum</i> Oocysts during Solar Photolysis of Free Available Chlorine

Abstract

Solar irradiation of aqueous solutions containing free available chlorine (FAC) dramatically enhances inactivation of Cryptosporidium parvum oocysts compared to FAC or sunlight alone. In pH 8, 10 mM phosphate buffer at 25 °C, exposure to FAC alone yields no oocyst inactivation at CTFAC ≤ 832 (mg min) L–1, while exposure to simulated sunlight alone for 60 min yields <0.5 log inactivation. In contrast, exposure to simulated sunlight for 60 min in the presence of [FAC]0 = 8 mg L–1 as Cl2 results in photolytic decomposition of FAC to ∼1 mg L–1 as Cl2 [yielding CTFAC ∼ 200 (mg min) L–1] accompanied by >2 log oocyst inactivation. Similar enhancement effects are observed in natural water under natural sunlight. Experiments undertaken in the presence of the reactive oxygen species (ROS) scavenger tert-butanol or in the absence of oxygen indicate that these enhancements are due to in situ ROS and ozone production via FAC photolysis.