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Water Science & Technology Vol 42 No 10 pp 179–186 © IWA Publishing 2000
Harmful cyanobacterial toxic blooms in waste stabilisation ponds
B Oudra*, M El Andaloussi**, S Franca***, P Barros****, R Martins*****, K Oufdou******, B Sbiyyaa*******, M Loudiki********, N Mezrioui********* and V Vasconcelos**********
*
Lab. d'Algologie, Faculté des Sciences-Semlalia-Marrakech,
Département de Biologie, Marrakech, Maroc
**
Laboratoire de pathologie Tensift 186, Bd. Mohamed -V-Marrakech, 40 000 Maroc
***
Lab. Microbiologia Exp., Instituto Nacional de Saude Ricardo Jorge, Av.
Padre Cruz 1699 Lisboa, Portugal.
****
Lab. Ecotoxicologia, Departemento de Zoologia e Antropologia,
Faculdade de Ciências, Universidade do Porto, 4050 Porto Portugal.
*****
Lab. Ecotoxicologia, Departemento de Zoologia e Antropologia,
Faculdade de Ciências, Universidade do Porto, 4050 Porto Portugal.
******
Lab. de Microbiologie, Faculté des Sciences-Semlalia-Marrakech,
Département de Biologie, Marrakech Morocco.
*******
Lab. d'Algologie, Faculté des Sciences-Semlalia-Marrakech,
Département de Biologie, Marrakech, Maroc
********
Lab. d'Algologie, Faculté des Sciences-Semlalia-Marrakech,
Département de Biologie, Marrakech, Maroc
*********
Lab. de Microbiologie, Faculté des Sciences-Semlalia-Marrakech,
Département de Biologie, Marrakech Morocco.
**********
Lab. Ecotoxicologia, Departemento de Zoologia e Antropologia,
Faculdade de Ciências, Universidade do Porto, 4050 Porto Portugal.
ABSTRACT
A coccoid picocyanobacterium Synechocystis sp. (0.6-2  m of cell
diameter) was found to be dominant during summer period in the experimental
wastewater stabilisation pond of Marrakesh. The taxonomy of this isolated
strain was confirmed by electron microscope study. The general patterns of
ultrastructure and the mode of cell division resemble Chroococcales. The
cyanobacterium strain was axenic and cultured on both inorganic Z8 and
BG13 media. Mammalian toxicity was confirmed by mice bioassay. The major
sympton of poisoning was severe diarrhoea. Histopathological study shows
a slight hepatotoxicosis associated with a pronounced change in the
intestinal mucosa which shows swelling and destruction of villi epithelium
and shedding of enterocytes into the lumen. Although slow, these kinds of
poisoning are comparable to those induced by okadiac acid intraperitoneal
mice injection (diarrhetic shellfish poisoning "DSP" toxins). By
using the enzyme-linked immunosorbent assay (ELISA), the amount ofhepatotoxins "microcystins" was determined. The result shows
that Synechocystis can produce a small amount of total microcystine
[an average of 15 g-1 dry weight corresponding to
20 ng(109cell)-1]. These findings lead us to consider
Synechocystis as both a potent neurotoxin and hepatotoxin producer.
Because of the confirmed cyanobacterium toxicity, an eventual ecological
implication should be considered. However, a toxic chronic test experiment
on Daphnia was simultaneously carried out. Juvenile D. magna (less
than 24 hours old), were fed three concentrations (104,
106, 108 cells / ml) of Synechocystis. A group of
organisms fed with Chlorella vulgaris (3. 105 cells/ml) and
another group without food, were studied as control treatments.
Only animals cultured with 104 cells/ml of cyanobacterium
survived at 80% until the end of the test (21 days). Reproduction and
normal growth occurred in control treatments fed with Chlorella vulgaris
and the group fed with the lowest concentration of Synechocystis. One-way ANOVA statistical analyses show significant differences in Daphnia
survival and growth, between treatments with and without Synechocystis
and between treatments with and without food. In terms of this study,
there is evidence that toxic picocyanobacteria blooms occurring in
wastewater stabilization ponds of Marrakesh, could have harmful
repercussions on zooplanktonic, bacteria and other algae communities.
Consequently, this will constitute a possible hindrance for sewage
self-purification process and system treatment performance. In addition,
the reuse of such treated wastewater effluent for irrigation will
constitute an additional, potent, health hazard for animals and
human's.
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