Biology Reference
In-Depth Information
results have been corraborated by the production of MC by the cultured isolates.
M
.
aeruginosa
thus
exhibited variability in MC content either from different blooms or from the same bloom sample
(Moreno
et al
., 2004). Toxic blooms have been frequently reported from Portugal particularly in some
of the rivers that fl ow from Spain (Ferreira
et al
., 2001; Vasconcelos, 1993; Rocha
et al
., 2002). Different
strains of
Oscillatoria
and
Phormidium
producing anatoxin-a or homoanatoxin-a caused dog deaths
(during 2002, 2003 and 2005) on the banks of Tarn River, France and pure cultures of eight strains
produced these neurotoxins (Cadel-Six
et al
., 2007).
A
.
circinalis
is a potential health hazard because of its distribution in freshwaters across Europe,
North America, Asia, South Africa, Japan, New Zealand and Australia (Baker, 1992). Moreover,
there is a geographical segregation in the type of toxins produced by this bacterium. For example,
strains from America and Europe produce only anatoxin-a (Schwimmer and Schwimmer, 1964;
Gibson and Smith, 1982) whereas Australian strains exclusively produce STXs (Carmichael, 1992;
Humpage
et al
., 1994).
No
.
spumigena
is wide spread in its occurrence within estuaries and coastal lagoons of Australia
(Jones
et al
., 1994; Heresztyn and Nicholson, 1997), Baltic Sea (Sivonen
et al
., 1989b), German North
Sea Coast (Nehring, 1993), New Zealand (Carmichael
et al
., 1988b) and North America (Galat
et al
.,
1990). Death of domestic animals upon consumption of bloom material of
No
.
spumigena
due to
massive liver failure has been reported from Australia, the Baltic Sea and New Zealand (Francis,
1878; Carmichael
et al
., 1988b; Nehring, 1993; Ressom
et al
., 1994).
VIII. METHODS OF CYANOBACTERIAL TOXIN REMOVAL
Cyanobacterial toxins are generally intracellular but due to environmental conditions or lysis of
cyanobacterial cells, the toxins tend to become extracellular and thus pose a great health risk to
human beings. For example, CYN can exist in extracellular state up to six weeks even after the
complete disappearance of the bloom of
C
.
raciborskii
(McGregor and Fabbro, 2000). A number of
methods have been proposed for intracellular and extracellular toxin removal. This subject has been
reviewed (Hitzfeld
et al
., 2000).
i) Intracelluar toxin removal
:
There are two methods that are generally employed. The fi rst is slow
sand fi ltration and the second is the membrane fi ltration. Both these methods are practised to remove
toxic cells from the waters by gently subjecting them to be separated from the water either by sand
fi ltration or membrane fi ltration. Slow sand fi ltration is cheap and can be used in large scale. This
generally enables fi ltration to be achieved gradually and slowly without subjecting any pressure on
the cells. A sand bed develops a biofi lm that allows biological degradation of dissolved substances.
At times overloading of cells can limit the effectiveness of sand fi ltration (Chorus and Bartram,
1999). Instead of sand fi ltration, riverbank fi ltration has been advocated in which the lake or river
water is made to pass across the soil on the bank. This has been termed as bank fi ltration (Miller
and Fallowfi eld, 2001). This is a cost effective and low maintenance technique. Batch adsorption
experiments with clay, sand and loam soils revealed more adsorption of MC-LR and nodularin in
clay soils. The soils with highest organic carbon content (2.9%) and the highest clay content (16.1%)
were found to be most effective in removing these toxins completely within 10-16 days in 2/3 soils
incubated in the dark at 20ºC (Miller
et al
., 2001a,b; Miller and Fallowfi eld, 2001). The degradation
has been largely attributed to both adsorption as well as degradation brought about by bacteria. The
German Federal Environmental Agency (UBA) conducted laboratory and fi eld experiments as well
as bank fi ltration studies. These infi ltration and bank fi ltration processes are normally considered as
