Harmful cyanobacterial toxic blooms in waste stabilization ponds

A coccoid picocyanobacterium Synechocystis sp. (0.6-2 mum of cell diameter) was found to be dominant during summer period in the experimental wastewat er stabilisation pond of Marrakesh. The taxonomy of this isolated strain wa s confirmed by electron microscope study. The general patterns of ultrastru cture and the mode of cell division resemble Chroococcales. The cyanobacter ium strain was axenic and cultured on both inorganic Z8 and BG13 media. Mam malian toxicity was confirmed by mice bioassay. The major symptom of poison ing was severe diarrhoea. Histopathological study shows a slight hepatotoxi cosis associated with a pronounced change in the intestinal mucosa which sh ows swelling and destruction of villi epithelium and shedding of enterocyte s into the lumen. Although slow, these kinds of poisoning are comparable to those induced by okadiac acid intraperitoneal mice injection (diarrhetic s hellfish poisoning "DSP" toxins). By using the enzyme-linked immunosorbent assay (ELISA), the amount of hepatotoxins "microcystins" was determined. Th e result shows that Synechocystis can produce a small amount of total micro cystine [an average of 15 mug(-1) dry weight corresponding to 20 ng(10(9)ce ll)(-1)]. These findings lead us to consider Synechocystis as both a potent neurotoxin and hepatotoxin producer. Because of the confirmed cyanobacteri um toxicity, an eventual ecological implication should be considered. Howev er, a toxic chronic test experiment on Daphnia was simultaneously carried o ut. Juvenile D, magna (less than 24 hours old), were fed three concentratio ns (10(4), 10(5), 10(6) cells/ml) of Synechocystis. A group of organisms fe d with Chlorella vulgaris (3.10(5) cells/ml) and another group without food , were studied as control treatments. Only animals cultured with 10(4) cell s/ml of cyanobacterium survived at 80% until the end of the test (21 days). Reproduction and normal growth occurred in control treatments fed with Chl orella vulgaris and the group fed with the lowest concentration of Synechoc ystis. One-way ANOVA statistical analyses show significant differences in D aphnia survival and growth, between treatments with and without Synechocyst is and between treatments with and without food. In terms of this study, th ere is evidence that toxic picocyanobacteria blooms occurring in wastewater stabilization ponds of Marrakesh, could have harmful repercussions on zoop lanktonic, bacteria and other algae communities. Consequently, this will co nstitute a possible hindrance for sewage self-purification process and syst em treatment performance, In addition, the reuse of such treated wastewater effluent for irrigation will constitute an additional, potent, health haza rd for animals and human's.