AN INVESTIGATION OF THE DEGRADATION OF MICROCYSTIN-LR
Report No FR0292

I Cousins and C D Watts

March 1992

SUMMARY

I OBJECTIVES To study the degradation of microcystin-LR in water, and identify degradation products.

II REASONS

Microcystin-LR is believed to be one of the more commonly occurring toxins produced by blue-green algal populations in the UK. Low concentrations of toxins may be released into water by blue-green algae during their normal growth cycle, and significant amounts of toxins may be released during algal cell lysis following blue-green algal blooms. Currently the fate of toxins in reservoirs, lakes or ponds is not known (e.g. they could be adsorbed onto sediments; chemical degradation could occur; biodegradation may take place) and there is concern relating to potential, unknown, degradation products.

III CONCLUSIONS

Chemical degradation of microcystin-LR does not appear to be an important route of removal from water, as the concentration of this toxin was not reduced over a 39 day period under a variety of pH and light regimes.

IV RECOMMENDATIONS

Further studies are necessary, using water samples and/or sediments taken from reservoirs which have experienced or are experiencing blue-green algal blooms, in order to study the microbial degradation of microcystin-LR.

V RESUME OF CONTENTS

Following a review of the literature relating to the degradation of blue-green algal toxins, experiments were designed to study the potential chemical degradation of microcystin-LR.

Four experiments were carried out in duplicate. Three pH regimes (pH 4, pH 7 and pH 9) were used, and in one experiment light was excluded.

No significant loss of microcystin-LR was observed during the 39 days of the experiments, which suggests that chemical degradation is not an important route of removal from environmental waters.

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