Investigação da aplicabilidade da turbidez e de bactérias esporogênicas aeróbias na avaliação da remoção de oocistos de Cryptosporidium spp. e cistos de Giardia spp em sistemas de abastecimento de água: uma abordagem de avaliação de risco

Abstract

In recent years, has been the subject of concern to researchers and health authorities the occurrence of pathogenic protozoa Cryptosporidium spp. and Giardia spp. in drinking water supplies, due to its characteristics of environmental persistence, low infective dose and highly resistance to commonly used disinfectants. Moreover, present methods for identification and quantification are expensive and laborious for routine analysis in the water supply systems (WSS). In this sense, the main objective of this study was to evaluate the use of turbidity and aerobic spore-forming bacteria such as parameters for monitoring the removal efficiency of Cryptosporidium spp. and Giardia spp. in WSS, inserted in a risk assessment approach associated with the presence of these protozoa in waters. To this end, the raw and finished water of the Rio das Velhas (RVS) and Vargem das Flores (VFS) systems were evaluated for analysis of Cryptosporidium and Giardia (oo)cysts, fortnightly, aerobic spore-forming bacteria, turbidity and Escherichia coli (this only in the raw water), weekly, from January to October 2011. The removal rates of each parameter were compared. A risk assessment was also performed to calculate the infection probability for both protozoa. There was an average concentration of 0.3 Cryptosporidium oocyst/L and 6.7 Giardia cyst/L, in the Velhas river, while in the dam of Vargem das Flores were detected, on average, 0.1 oocyst and cyst/L. For spore-forming bacteria were found 2.0x103 to 3.4x105 cfu/L in RVS raw water, while in the VFS this microorganism concentrations ranged from ND to 7.4x104 cfu/L. For turbidity, the values in the raw water ranged from 2.71 to 250 NTU at RVS, and finished water obtained values between 0.11 and 5.13 NTU, whereas the VFS values of this parameter were between 0.88 and 7.53 NTU in raw water and 0.11 and 1.08 NTU in finished water. Also in respect to the E. coli concentrations, there were higher values for the RVS, where they accounted from 1.0x102 to 1.5x104 MPN/100 mL while in VFS was founded concentrations from ND to 64.4 MPN/100 mL. Both aerobic spore-forming bacteria as turbidity did not correlate significantly with the protozoa, however, both variables are important as indicators in studies of Cryptosporidium and Giardia (oo)cysts removal. Also it was observed that the RVS and VFS waters shown a risk to the public health in relation to the presence of the protozoa under study higher than acceptable to the American standard, but similar to Canadian law and WHO guidelines. We recommend proceed of studies assessing the pathogenic protozoa occurrence and removal.