THE PERSISTENCE OF ANATOXIN-A IN RESERVOIR WATER
Report No FR0427

C Smith and A Sutton

Dec 1993

SUMMARY

I BENEFITS

It has been shown that anatoxin-a, a neurotoxin produced by several blue-green algae including Anabaena and Oscillatoria species, has a limited persistence in reservoir waters at ambient pH. Its half life is about five days. Following the determination of a level of interest, it will be possible to predict how long it will take high levels of this toxin in water (e.g. following an algal bloom) to fall to acceptable levels. This will be beneficial should additional treatment be required when high levels of anatoxin-a are present in reservoir waters, or if decisions as to recreational use need to be taken.

II OBJECTIVE

To establish the persistence of anatoxin-a in reservoir waters.

III REASONS

Anatoxin-a is a mammalian neurotoxin which is known to have caused animal deaths when large numbers of toxin-containing blue-green algal cells have been ingested. Typical levels of this toxin in water are currently not known, but based on information on levels of another blue-green algal toxin (microcystin-LR) in reservoir waters, it is likely that levels will only be high following algal blooms when toxin is released from large numbers of senescent cells. It is important to determine the persistence of anatoxin-a to allow operational decisions to be taken regarding treatment for water supply, or to decide on access for recreational use, following algal blooms.

IV RESUME OF CONTENTS

The persistence of anatoxin-a was monitored using a previously developed analytical method (FR0363) involving solid phase extraction and analysis by high performance liquid chromatography (HPLC) with ultra-violet (UV) detection. Initial laboratory experiments were carried out with reservoir water spiked with anatoxin-a at different pH under normal day-night light conditions, and in the absence of light. It was found that although anatoxin-a in reservoir water was stable at pH 4 for at least 21 days, at pH 8 or 10 less than 5% of the original level (10 µg1^-1) was detectable after 14 days. Further experiments, with more intensive monitoring, were conducted with and without reservoir bed-sediment present. In the presence of bed sediment, the half-life of anatoxin-a in reservoir water was about five days.

V CONCLUSIONS

In laboratory experiments, under normal pH conditions and in the presence of natural microbial populations from bed-sediment, anatoxin-a is not particularly persistent in reservoir water. Its half life is about five days.

VI RECOMMENDATIONS

Levels of anatoxin-a in reservoir waters should be determined to ascertain typical levels during and after blue-green algal blooms, to confirm the findings of these laboratory experiments.

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