Cryptosporidium sp. and Giardia sp. in the St. Lawrence River: Impact on drinking water quality.

Abstract

This study was designed to: (a) describe the occurrence and distribution of the protozoan parasites Cryptosporidium sp. and Giardia sp. in raw and treated water supplies on the St. Lawrence River; (b) to find a suitable microbial indicator for the presence of Cryptosporidium sp. and Giardia sp. in raw water; (c) to measure the survival capability of Cryptosporidium parvum in both the raw water and the treated water supplies of the St. Lawrence River, and (d) to determine whether C. parvum oocysts aged (or stressed) in raw water are more susceptible than fresh oocysts to chlorine and monochloramine disinfection. Twelve sampling sites were chosen on the St. Lawrence River (between Morrisburg and Lancaster, Ontario), consisting of eight raw surface water sites, and four water treatment plant effluents. Two of the plants practiced full conventional treatment of the water, including alum coagulation, rapid-sand filtration and chlorination, while the other two used a one-step chlorination process to treat the drinking water. Each site was sampled three times between July and November 1995, and a further 5 to 7 times between April and October 1996. (Abstract shortened by UMI.)