Toxic cyanobacteria (blue-green algae) are becoming recognized as a gr
eater water quality problem as blooms become more common in waters aff
ected by increasing nutrient levels, and knowledge of the properties o
f the toxin increases. Of particular importance are the hepatotoxic cy
clic peptides produced by certain strains of Microcystis species and b
y Nodularia spumigena. The effects of chlorine and chloramine on these
hepatotoxins in both freeze-dried and intact material were investigat
ed. The destruction of the toxins was monitored using HPLC analysis. I
n a number of cases mouse bioassays were used for confirmation of the
destruction of the toxins and to ensure that toxic by-products, not de
tectable by HPLC, were not formed. Contrary to evidence reported in th
e literature, chlorine was effective in destroying toxins, as long as
sufficient chlorine was used. Toxins were destroyed under conditions s
uch that a chlorine residual of at least 0.5 mg/l was present after 30
min contact time. The destruction of toxins was pH dependent; chlorin
ating agents such as calcium and sodium hypochlorite were not as effec
tive at high dose rates due to elevation of pH, Chloramination had lit
tle effect on toxins. Although the degradation mechanisms have yet to
be established, the results show that chlorination may be an effective
and practical method for the removal of cyanobacterial peptide toxins
from drinking water.