*6.1.4 Chlorine*

Chlorine reacts with microcystins, cylindrospermopsin, and saxitoxins to a lesser amount. Anatoxin-a does not seem to react well with chlorine. In addition, saxitoxin inactivation works best at higher pH levels, whereas microcystin inactivation works best at lower pH levels. The pH of the water and the presence of NOM affect the reactivity of chlorine with contaminants. Depending on the water quality circumstances, the contact time (CT) values necessary for the elimination of microcystins with free chlorine may be many times higher than those required for the surface water treatment rule. Chloramine and chlorine dioxide in commonly used levels have not been shown to be effective against any of the four poisons. Chloramines are effective against microcystins at very high doses and over long periods.

## *6.1.5 Ozone*

Microcystins, anatoxin-a, and cylindrospermopsin react more quickly with ozone than with other common oxidants. Saxitoxin is the one that is least affected by ozone. Only 20% of the saxitoxins present would be destroyed under equivalent settings when microcystins would be fully removed. Although hydrogen peroxide alone is ineffective in removing pollutants, ozone combined with hydrogen peroxide is significantly more powerful (**Table 3**).


**Table 3.**

*General effectiveness of blue-green algal toxin inactivation with specific oxidants [19].*
