Toxicity evaluation of Microcystis aeruginosa cultures and natural cyanobacteria blooms from reservoirs of Tietê river, SP / Avaliação da toxicidade de Microcystis aeruginosa e de florações naturais de cianobactérias de reservatórios do rio Tietê, SP
Renata Akemi Takenaka
DATA DE PUBLICAÇÃO
The effects of cyanobacteria upon aquatic organisms were evaluated, aiming to characterize and quantify the toxins of both, a monospecific cyanobacterial culture and material from natural blooms occurring in the reservoirs of Tietê river, SP. The already known toxic strain NPLJ-4 of Microcystis aeruginosa was cultured in ASM-1 medium at 25 Celsius degrees and 12h light/12h dark in the incubator, in order to evaluate its toxicity at different stages of the culture growth by ecotoxicological tests using the cladocerans Ceriodaphnia dubia and C. silvestrii as test-organisms. These tests were carried out according to the procedures standardized by ABNT, in order to evaluate also the toxicity of natural blooms and the efficiency of different water treatment processes in removing cells, microcystins and by-products of cyanobacteria. The results obtained indicated an increase in the concentration of microcystins along the cyanobacterial culture growth. Extracts from the stationary phase of the culture were less toxic compared with those from the other phases which had acute toxicity and adversely affected cladoceran survival, resulting in EC50; 48h values of 1,4 - 4,7 × 10 POT.6cells/mL (middle exponential phase), 1,6 - 8,7 × 10 POT.6cells/mL (final exponential phase), 7,5 - 14,1 × 10 POT.6cells/mL (stationary phase) and 1,9 - 4,6 × 10 POT.6cells/mL (senescent phase) for C. dubia; and 1,9 - 5,4 × 10 POT.6cells/mL (middle exponential phase), 1,6 - 10,9 × 10 POT.6cells/mL (final exponential phase), 10,2 - 15,4 × 10 POT.6cells/mL (stationary phase) and 2,0 - 4,2 × 10 POT.6cells/mL (senescent phase) for C. silvestrii. Cells of Microcystis (Microcystis aeruginosa, M. panniformis and M. protocystis) and Pseudanabaena mucicola were cyanobacteria species dominant in the Barra Bonita reservoir and cells of Microcystis (M. aeruginosa and M. panniformis), in the Promissão reservoir. The dominance of cyanobacteria in both studied reservoirs was related to the stability of the water column, N/P ratios of 8 to 13 (Barra Bonita) and 19 to 20 (Promissão), high water temperatures (19 - 30°C for Barra Bonita and 26 - 28°C for Promissão) and high nutrient availability (0,05 - 0,26 mg/L total phosphorus for Barra Bonita, and 0,01 - 0,05 mg/L total P for Promissão) as a consequence of the trophic state of the reservoirs. The water from Barra Bonita reservoir during the cyanobacterial blooms was more toxic to daphnids than that from Promissão reservoir. Crude extracts from all cyanobacteria blooms tested presented microcystins (239 - 1647 µg/L for Barra Bonita and 192 - 1295 µg/L for Promissão) and caused acute toxicity to daphnids, resulting in EC50; 48h values of 87 - 282 mg/L (Barra Bonita) and 146 - 428 mg/L (Promissão) for C. dubia, and 98 - 546 mg/L (Barra Bonita) and 110 - 391 mg/L (Promissão) for C. silvestrii. Crude extracts concentrations above 80 mg/L to Barra Bonita and 100 mg/L to Promissão adversely affected the survival and reproduction of daphnids. The results obtained evidenced the risks to the natural biota and possibly to the human health, and can therefore jeopardize the multiple uses of the reservoirs. They reveal the urgent necessity for remedial action, particularly to slow down and to prevent eutrophication.
fitoplâncton testes de toxicidade cyanobacteria microcystins nplj-4 strain extratos brutos toxicity tests linhagem nplj-4 microcystis microcystis dafinídeos phytoplankton daphnids microcistinas crude extracts cianobactérias
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