Occurrence of Cryptosporidium oocysts and Giardia cysts in public water supplies in Vitória, ES, Brazil

Abstract

This study aimed to investigate the occurrence of Cryptosporidium oocysts and Giardia cysts in raw, filtered, and chlorinated waters collected from two drinking water treatment plants (WTP A and WTP B). WTP A uses either direct filtration or flotation-filtration depending on the turbidity of raw water. WTP B has two independent treatment lines, a direct filtration and a conventional treatment line. Cryptosporidium oocysts and Giardia cysts were concentrated by flocculation, identified by direct immunofluorescence microscopy and confirmed by DAPI staining and phase-contrast microscopy. In raw water, the occurrence of cysts was from 75 (WTP A) to 100% (WTP B) of the samples, and of oocysts from 66.6 (WTP A) to 83.3% (WTP B). Both protozoa were detected in water treated by direct filtration (cysts: < 0.27 to 20.0 cysts L-1; oocysts: < 0.48 to 22.5 oocysts L-1) and flotation-filtration (cysts: < 0.27 to 5.0 cysts L-1; oocysts: < 0.48 to 17.5 oocysts L-1). The absence of cysts and oocysts in chlorinated water does not exclude risks, as the limitations of concentration and identification techniques must be considered, given the low recovery rates, especially in water with low turbidity (15.5 – 72.7% of Giardia; 3.6 – 38.5% of Cryptosporidium). In the raw water samples from WTP A, a moderate correlation was observed between the protozoa, and these with the conventional parameters of water quality. In the raw water samples from WTP B, the correlation was insignificant. These results reinforce the importance of monitoring protozoa in water destined for public supply.