Occurrence of toxin-producing cyanobacteria blooms in a Brazilian semiarid reservoir

I A S Costa,S M Costa,P A C Senna,S M F O Azevedo,N T Chellappa,R R Bernardo

doi:10.1590/s1519-69842006000200005

Abstract

We report the occurrence of cyanobacterial blooms and the presence of cyanotoxins in water samples from the Armando Ribeiro Gonçalves reservoir (06 degrees 08 S and 37 degrees 07 W), located in the state of Rio Grande do Norte, in the semiarid region of northeastern Brazil. The cyanobacterial species were identified and quantified during the rainy and dry seasons in the year 2000. Cyanotoxins such as microcystins, saxitoxins and cylindrospermopsins were analyzed and quantified using HPLC and ELISA methods. The mixed toxic blooms of Cylindrospermopsis raciborskii, Microcystis spp (M. panniformis, M. protocystis, M. novacekii) and Aphanizomenon spp (Aphanizomenon gracile, A. cf. manguinii, A. cf. issastschenkoi) were persistent and represented 90-100% of the total phytoplankton species. Toxic cyanobacterial blooms from the Armando Ribeiro Gonçalves reservoir were analyzed and found to have three phases in relation to the annual cycle. During the rainy season, an intense toxic bloom of Cylindrospermopsis raciborskii was recorded along with saxitoxins (3.14 microg.L(-1)). During the transition period, between the rainy and dry seasons, different species of Microscytis occurred and microcystin as high as 8.8 microg.L(-1) was recorded. In the dry season, co-dominance of Cylindrospermopsis raciborskii, Microcystis spp and Aphanizomenon spp occurred and the concentrations of saxitoxin remained very low. Our results indicate the presence of microcystins (8.8 microg.L(-1)) and saxitoxins (3.14 microg.L(-1)) into the crude water, with increasing concentrations from the second fortnight of April to late May 2000. The occurrence of toxic blooms in this reservoir points to a permanent risk of cyanotoxins in supply waters, indicating the need for the implementation of bloom control measures to improve the water quality. Exposure of the local population to cyanotoxins through their potential accumulation in fish muscle must also be considered.

Highlights

Eutrophication is the result of uncontrolled human population growth and the discharge of urban, industrial and agriculture effluents into the aquatic ecosystems of several countries, including Brazil (Tundisi & Matsumura-Tundisi, 1992)
This paper work reports on the presence of high density potentially toxic cyanobacterial cells, and the presence of microcystins and saxitoxins in raw water seston samples from the Armando Ribeiro Gonçalves reservoir, the Pataxó channel, and treated water distributed through this system
The phytoplankton community of the Armando Ribeiro Gonçalves reservoir presented a cyanobacterial predominance of 90-100% of the total phytoplankton density in the raw water in 2000

Summary

Introduction

Eutrophication is the result of uncontrolled human population growth and the discharge of urban, industrial and agriculture effluents into the aquatic ecosystems of several countries, including Brazil (Tundisi & Matsumura-Tundisi, 1992). This represents a primary problem for water management all over the world, especially in dry regions, since one of the major consequences of eutrophication is the appearance of cyanobacterial blooms (Carmichael, 2001; Falconer, 2001; Azevedo et al, 2002). Human deaths occurred through the “Caruaru Syndrome”, attracting worldwide attention when 52 patients died from cyanobacterial hepatotoxins after undergoing renal dialysis (Jochimsen et al, 1998). Teixeira et al (1993) showed a strong correlation between cyanobacterial blooms in the Itaparica reservoir (Bahia) and the death of 88 people, among 200 intoxicated after drinking water from the reservoir between March and April 1988

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