DETECTION AND REMOVAL OF CYANOBACTERIAL TOXINS FROM FRESHWATERS
Report No FR0211

H James and J K Fawell

June 1991

SUMMARY

I OBJECTIVES

  1. To characterise and quantify peptide hepatotoxins (microcystins) from freshwater cyanobacteria.
  2. To investigate the efficiency of water treatment processes to remove or detoxify cyanobacterial toxins in water.
  3. To investigate new methods for toxin removal/detoxification if the standard methods in 2 proved to be inadequate.

II REASONS

Blooms of blue-green algae, which have been increasing in recent years, have the potential to cause problems for the water supply industry. When this research was initiated, little was known about the character of the toxins or the levels at which they occurred in freshwaters. Their behaviour under typically used water treatment regimes was also unclear, and there was a need to establish whether new treatment processes needed to be developed to safeguard public water supplies.

III RESUME OF CONTENTS

A method has been developed for the analysis of microcystins in water. This involves solid-phase extraction, and analysis using high-performance liquid chromatography with diode array (ultra-violet) detection. However, further development of this method is required to reduce the limit of detection and to improve the quantification.

The effects of coagulation, powdered activated carbon (PAC), chlorination and ozonation on the levels of microcystins in waters containing "algal blooms" were investigated. Coagulation resulted in increased levels of microcystins in the treated water, due to release of toxins from cells lysed during the treatment. PAC, used at levels typical for water treatment, reduced the levels of microcystins in treated waters, but complete removal required high PAC doses. There were no detectable chlorinated products produced when microcystin-LR was reacted with dilute sodium hypochlorite, and the effects of chlorination were not pursued. Ozonation rapidly destroyed the toxicity of microcystin-LR. Although the reaction products were not identified, they were shown to be non-toxic in the mouse bioassay test.

IV CONCLUSIONS

A method for analysing microcystins in water has been developed. The use of diode array detection allows greater specificity than single-wavelength UV detection.

Of the treatment processes studied, ozonation appears to be the most promising, as the microcystin toxins are rapidly destroyed. Further work is necessary to confirm that ozonation produced no toxic products.

Copies of the Report are available from FWR, price 15 less 20% to FWR Members.