Analysis of distribution, density and toxicity of cyanobacterial blooms and its toxins in the reservoirs of Middle and Low Tietê river (SP) and its relation with limnological characteristics of this system / Análise da distribuição, densidade e toxicidade de florações de cianobactérias em reservatórios do médio e baixo rio Tietê (SP) e relação com as características limnológicas do sistema

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Reservoirs in Brazil, particularly in São Paulo State, are important ecosystems which were built up successively in the last 40 years. Some of these reservoirs, mainly at the Middle and the Low Tietê river cascade system are eutrophic. Frequently cyanobacterial blooms are related to these eutrophic conditions which compromise the multiple use of the reservoir, implicating risk to human health and aquatic biota. This study aims to investigate occurrence, distribution and frequency of cyanobacterial blooms in these reservoirs, just as quantify cyanotoxin concentrations, and toxicity of these blooms, relating with physical and chemical environmental parameters as inductors of the dominant of cyanobacteria. Samples (10 L) of cyanobacterial blooms were collected near to the six reservoirs of the Middle and Low Tietê river (Barra Bonita, Bariri, Ibitinga, Promissão, Nova Avanhandava and Três Irmãos), between November/2002 and October/2003. Samples of cyanobacterial blooms were taking from each reservoir with plankton net (20 mm). Aliquot (100 mL) of samples were collected and preserved (formalin 4 %) for laboratory identification and quantification. The material remaining were frozen and lyophilized for determination and quantification of cyanotoxins, and for ecotoxicological tests. The water physical and chemical variables were evaluated in situ, as well as complementary water samples were collected with a water-pump integrating all the water column to analysis of total and dissolved nutrients, chlorophyll-a and the composition phytoplankton community. The tests of toxicity of different concentrations of cyanobacterial extracts (lyophilized) were carried out by exposition of neonates of Daphnia similis, Ceriodaphnia dubia, and Ceriodaphnia silvestrii (48h), and intraperitoneal injection in Swiss albino mice (24h). The results demonstrate that the Chlorophyceae class had the higher richness of species, while Cyanophyceae had the higher frequency and density of organisms in analysed samples. Toxic cyanobacteria, mainly of genera Microcystis, Anabaena, Cylindrospermopsis, Raphidiopsis and Planktothrix, were found in all samples collected. Cyanotoxins, mainly microcystins, were detected in the majority of reservoirs which values were between 2.17 and 150 mü g/L. However, paralytic toxins, such as saxitoxins, were found in some reservoirs, which maximum values ranged from 4.53 to 6.93 mü g eq. STX/L. All tested samples were toxic, with range of CE IND.50 -48h in the microcrustaceans, from 0.10 - 1.32 mg/mL (d.w.) to Daphnia similis, from 0.2 - 1.70 mg/mL (d.w.) to Ceriodaphnia dubia and from 0.09 - 1.20 mg/mL (d.w.) to Ceriodaphnia silvestrii. With respect to Swiss albino mice test, DL IND.50 -24h varied from 48 - 904 mg/kg (d.w.). Although was demonstrated gradual reduction of nutrients downstream, mainly phosphorus and nitrogen (total and dissolved), indicating the depurative capacity of cascade reservoirs sequence, the present study still has demonstrated the maintenance of favorable conditions to development of to toxic cyanobacterial blooms in all the reservoirs. Results demonstrate that the continuous eutrophication process and toxic cyanobacterial blooms in these reservoirs could represent a potential risk to the aquatic biota and human populations who use these waters for multiple purposes. This situation represents a challenge in the management of cascade system, according to reservoirs operational system, such as water residence time and other factors which should be considered in these constructions

ASSUNTO(S)

ecotoxicology phytoplankton reservoirs rio tietê cyanobacteria ecotoxicologia tietê river cianotoxinas reservatórios cyanotoxins cianobactérias fitoplâncton

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