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

• Published in: Engenharia Sanitaria e Ambiental 2024, Vol.29
• Main Authors: Keller, Regina De Pinho, Santos, Rodrigo, Covre, Marcus Andrade, Coelho, Edumar Ramos Cabral
• Format: Article
• Language: English
• Subjects: WATER RESOURCES
• ISSN: 1413-4152; 1809-4457; 1809-4457
• DOI: 10.1590/s1413-415220230065

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. RESUMO Este estudo teve como objetivo investigar a ocorrência de oocistos de Cryptosporidium e cistos de Giardia em águas brutas, filtradas e cloradas, coletadas de duas estações de tratamento de água potável (ETA A e ETA B). A ETA A utiliza filtração direta ou flotação-filtração dependendo da turbidez da água bruta. A ETA B possui duas linhas de tratamento independentes, uma de filtração direta e outra de tratamento convencional. Os oocistos de Cryptosporidium e cistos de Giardia foram concentrados por floculação, identificados por microscopia de imunofluorescência direta e confirmados por coloração com DAPI e microscopia de contraste de fase. Na água bruta, a ocorrência de cistos variou de 75% (ETA A) a 100% (ETA B) das amostras, e de oocistos de 66,6% (ETA A) a 83,3% (ETA B). Ambos os protozoários foram detectados na água tratada por filtração direta (cistos: ETA A e B < 0,27 a 20,0 cistos