Evaluationof Copper Algicides for the Control of Algae and Cyanobacteria

ReportNo WSAA 130

April 1998

SYNOPSIS

Thisstudy reports on laboratory and field trials to compare the relative toxicityand persistence of the algicides, copper sulphate and the copper chelateCOPTROLÒ to green algaeand cyanobacteria. Laboratory toxicity tests in moderately hard synthetic watershowed a wide range of sensitivity of up to an order of magnitude between greenalgal species. There was no difference in relative toxicity between CuSO₄.5H₂Oand COPTROLÒ for the mostsensitive species (Selenastrumcapricornutum, Scenedesmus obliguus), whereas for the more tolerant species(Chlorella vulgaris, Ankistrodesmus sp.)CuSO₄.5H₂O was approximately 4 to 5 times more toxic thanCOPTROLÒ on a Cu weightbasis under these test conditions. There was also no difference in the relativetoxicity of the two algicides to the cyanobacterium Microcystis aeruginosa. Two separate field trials were carried in areservoir using large volume environmental enclosures to evaluate thepersistence and residual toxicity of the two algicides in natural water. Thefirst trial, at copper concentrations considerably above those normally appliedin copper dosing, showed relatively slow loss of copper, and a residual toxiceffect 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 coppersulphate or COPTROLÒ. The toxicity ofboth algicides declined rapidly and the water was no longer toxic to thecyanobacterium Microcystis aeruginosa.Two separate field trials were carried in a reservoir using large volumeenvironmental enclosures to evaluate the persistence and residual toxicity ofthe two algicides in natural water. The first trial, at copper concentrationsconsiderably above those normally applied in copper dosing, showed relativelyslow loss of copper, and a residual toxic effect in the water for at least 22days. In the second trial, at lower doses, there was rapid loss of copper fromthe water whether it was applied as copper sulphate or COPTROLÒ. The toxicity of bothalgicides declined rapidly and the water was no longer toxic to thecyanobacterium Anabaena circinalisafter 24 hours. Field studies were also undertaken to evaluate the use ofaircraft versus boats for copper sulphate application. On-site monitoring ofcopper dispersal following application showed short-term high concentrations ofboth 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 butresulted in lower maximum ionic copper concentrations at the surfaceimmediately after application. This suggested that aerial application may proveless effective in terms of maximising toxic effect to target organisms.

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