Ocorrência de cianobactérias em manancias de abastecimento de água para consumo humano no município de Viçosa MG

• Autor(a) principal: Magalhães, Adriana Barbosa Sales de
• Data de Publicação: 2007
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2542
• topic: Cianobactérias; Toxinas; Mananciais; Cyanobacteria; Toxin; Water sources; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA

Considering the increase in toxic cyanobacterial blooms and the high cost of toxin removal using conventional systems of water treatment, monitoring cyanobacteria in the public supply springs is fundamental to evaluate the risks of a possible toxin-producing strain. The objectives of the present work were to identify and quantify cyanobacteria found in springs of water sources for the public supply system in the municipal district of Viçosa- MG; associate cyanobacterial cell density with limnological variables; identify seasonal patterns of cyanobacteria populations; isolate genera and species of cyanobacteria and store in culture bank and investigate the microcystin production in potentially toxic species using the ELISA Test (Enzime-Linked Immuno Sorbent Assay). Water samples were collected from the rivers São Bartolomeu and Turvo Sujo, both being sources for capturing water used for public supply in the city of Viçosa. The following physical, chemical and physicochemical water variables were analyzed: temperature, pH, dissolved oxygen, total nitrogen, total phosphorus, nitrate, ammonium and alkalinity. Monthly sample collections were carried out in four selected sites (P1, P2, P3 and P4) from September/05 to August/06. The samples for qualitative phytoplankton analysis were collected by horizontal towing a 20 μm plankton net through the surface of the water column. Subsurface crude water samples (20-cm depth) were collected with a flask for the quantitative analysis. The isolated species were kept in growth chamber under photoautotrophic conditions. During the period of study, 18 taxa were identified, totaling four orders: Chrooccocales (11.1%); Oscillatoriales (38.9%); Nostocales (44.4%) and Stigonematales (5.6%). Nostocales and Oscilatoriales were the orders with the largest numbers of representatives, with eight and seven taxa respectively, followed by the orders Chrooccocales (2) and Stigonematales (1). Three genera were identified in the order Nostocales, which were represented by the taxa Anabaena ambigua, A. inaequalis, Calotrhrix braunii, Nostoc cf. carneum, N. commune, N. microscopicum, N. cf. muscorum and Nostoc sp. The order Oscilatoriales had five genera identified, which were represented by the taxa: Geitlerinema splendidum, Limnothrix sp., Oscillatoria subbrevis, Phormudium granulatum, P. cf. retzii, Pseudanabaena galeata and P. catenata. The order Chrooccocales was represented by two genera with a single species in each genus; Synechococcus nidulans and Synechocystis cf. aquatilis. The order Stigonematales included only one genus (Stigonema), with non-identified species. The cyanobacterial cell densities found in the four sampled sites were below the determination of the Brazilian Ministry of Health s Directive 518 of 25 March 2004 on the monitoring the quality of water intended for human consumption. The species Nostoc cf. commune had positive result for microcystin in the sites P1, P2 and P3. The Canonical Correspondence Analysis through the Monte Carlo test showed that the analyzed variables had no significant influence on cyanobacterial cell densities. No regular pattern of cyanobacteria distribution was observed in the sampled sites during the period of study. Routine water source monitoring is recommended as part of ETA's operations, as a preventive measure for the occurrence of potentially toxic cyanobacterium strains. A manual for the identification of the cyanobacteria found in the studied water sources was developed to aid the work of the technicians in charge of the quality of water, which certainly will facilitate species recognition, making it possible the necessary measures in the public water treatment operation, in case an increase in cell density occurs, particularly of potentially toxic species.