Evaluation of Copper Algicides for the Control of Algae and Cyanobacteria

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Evaluation of Copper Algicides for the Control of Algae and Cyanobacteria

Report no. UWRAA 130

April 1998

SYNOPSIS

This study reports on laboratory and field trials to compare the relative toxicity and persistence of the algicides, copper sulphate and the copper chelate COPTROL to green algae and cyanobacteria. Laboratory toxicity tests in moderately hard synthetic water showed a wide range of sensitivity of up to an order of magnitude between green algal species. There was no difference in relative toxicity between CuSO4.5H2O and COPTROLÒ  for the most sensitive species (Selenastrum capricornutum, Scenedesmus obliguus), whereas for the more tolerant species(Chlorella vulgaris, Ankistrodesmus sp.) CuSO4.5H2O was approximately 4 to 5 times more toxic than COPTROL on a Cu weight basis under these test conditions. There was also no difference in the relative toxicity of the two algicides to the cyanobacterium Microcystis aeruginosa.

Two separate field trials were carried in a reservoir using large volume environmental enclosures to evaluate the persistence and residual toxicity of the two algicides in natural water. The first trial, at copper concentrations considerably above those normally applied in copper dosing, showed relatively slow loss of copper, and a residual toxic effect in the water for at least 22 days. In the second trial, at lower doses, there was rapid loss of copper from the water whether it was applied as copper sulphate or COPTROL. The toxicity of both algicides declined rapidly and the water was no longer toxic to the cyanobacterium Microcystis aeruginosa after 24 hours.

Field studies were also undertaken to evaluate the use of aircraft versus boats for copper sulphate application. On-site monitoring of copper dispersal following application showed short-term high concentrations of both total and labile copper at the surface, particularly for boat dosing. These high levels were rapidly diluted and complexed to less toxic fractions. The comparison indicated that aerial dosing gave more even dispersal but resulted in lower maximum ionic copper concentrations at the surface immediately after application. This suggested that aerial application may prove less effective in terms of maximising toxic effect to target organisms.

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