CYANOBACTERIAL TOXINS - Cyanobacteria - page 571

not be derived. However, a total guideline value for MC-LR (free plus cell bound) of 1 µg L -1 was set
as a safer MAC (WHO, 2003). Based on the studies available on HABs in different countries, the levels
of cyanobacterial toxins in potable waters and the overall risk assessment to human beings, now draft
guidelines have been prepared by each country (Chorus, 2005). These guidelines cover safer limits
of cyanobacterial toxins for potable and recreational waters. Variations from the general limit of 1
µg L -1 MC-LR equivalents have been proposed taking into consideration the average weight of the
citizen and the proportion of TDI attributed to the consumption of water. In Australia, the guideline
value was set at 1.3 µg L -1 MC-LR equivalents considering the average weight of a citizen as 60 kg
and a proportion of daily intake at 0.9. In the absence of toxin monitoring data it was suggested to
take into account the cell numbers of HABs. If toxic M . aeruginosa occurs in potable waters, 6,500
cells ml -1 is considered equivalent to 1.3 µg L -1 MC-LR equivalents (giving a toxic cell quota of 0.2
pg total MCs cell -1 ). Potential health risk from recreational waters is considered a possibility when
the cell number of toxic blooms would correspond to 20,000 cells ml -1 . Likewise, increasing risk to
livestock health is likely when the concentration of MCs exceeds 2.3 µg L -1 MC-LR equivalents and
a corresponding cell number of Microcystis population estimated to be 11,500 cells ml -1 . Although
guidelines for fi sh and shellfi sh in Australia are not available, health alert levels for toxins in fi shes,
prawns and mussels in the state of Victoria, Australia have been proposed (Van Buynder et al ., 2001).
The critical concentrations in seafood are determined for fi shes (250 µg kg -1 ), prawns (1,100 µg kg -1 )
and mussels (1,500 µg kg -1 ) taking into account TDI level for adults. Brazil adopted the standard
value of 1 µg L -1 for MCs as mandatory and values of 3 µg L -1 for STXs and 15 µg L -1 for CYN were
recommended guidelines. Besides these, a general alert is given when the toxic cyanobacterial cells
exceed 20, 000 cell ml -1 and the application of algicides during water purifi cation process is forbidden.
A MAC of 1.5 µg L -1 for MC-LR in drinking water in Canada was adopted and a comprehensive
plan is under preparation for including other MC variants. In New Zealand, the guideline values
for MCs, nodularins and CYN are 1 µg L -1 whereas 6, 1, 2, and 3 µg L -1 have been prescribed for
anatoxin-a, anatoxin-a(s), homoanatoxin and STXs, respectively. It is to be noted that except for MCs,
WHO (2004) does not have guideline values for other cyanobacterial toxins. Countries such as Czech
Republic, Finland, France, Germany, Hungary, Poland, South Africa and Spain adopted the WHO
guideline value of 1 µg L -1 for MC-LR. Although there are no offi cial guidelines for cyanobacterial
toxins in countries like Belgium and Luxembourg, Denmark, Greece and Italy, depending on the
requirements the WHO guideline of 1 µg L -1 for MC-LR is adopted. There are no federal regulatory
guidelines for either cyanobacteria or their toxins in the USA but they have been included in the
US Environmental Protection Agency “ Contaminant candidate list ” for further research to clarify the
need for further regulation. However, several state or local authorities adopted a regulatory limit
of 1 µg L -1 MC-LR equivalents.
X. PROTOCOLS FOR WATER TREATMENT
In order to provide potable water to the people every regulatory authority takes enough precautions
during water treatment in treatment plants. Conventional water treatment plants during the 1960s and
1970s mainly relied on pre-chlorination and post-chlorination steps combined with the intervening
steps of coagulation, fl occulation, settling and sand fi ltration (Fig. 27 ). The inherent danger invoved in
such treatment is that the pre-chlorination may cause lysis of the toxic blooms leading to an increase
in the toxin content beyond the acceptable guidelines of WHO. In the absence of regular monitoring
of surface waters for the development of blooms and if the number of toxic cyanobacterial cells
exceeds the moderate adverse health effects to high risk level, then such treatments do not meet the