Diquat associated with copper sources for algae control: Efficacy and ecotoxicology

Area of Science:

• Environmental Science
• Aquatic Toxicology
• Ecotoxicology

Background:

• Algal blooms pose significant challenges in aquatic ecosystems, impacting water quality and biodiversity.
• Effective and selective control of nuisance algae is crucial for maintaining ecological balance.
• Copper compounds and diquat are commonly used algaecides, but their efficacy and non-target effects require thorough evaluation.

Purpose of the Study:

• To assess the efficacy of copper oxychloride, copper hydroxide, and diquat in controlling Ankistrodesmus gracilis and Pithophora kewesis.
• To determine the acute toxicity of these algaecides and their combinations on non-target aquatic organisms.
• To identify the most effective algaecide and its optimal concentration for specific algal species.

Main Methods:

• Algal growth inhibition was quantified using chlorophyll a and pheophytin a measurements.
• Efficacy was determined by calculating the percentage of growth inhibition at various chemical concentrations.
• Acute toxicity was evaluated by determining the 50% lethal concentration (LC50) for non-target organisms.

Main Results:

• Copper sources demonstrated high efficacy (>95%) against A. gracilis at concentrations as low as 0.1 mg L(-1).
• Diquat and its combination with copper hydroxide were effective against A. gracilis at 0.4 mg L(-1), achieving 95% and 88% control, respectively.
• Copper oxychloride showed 93% efficacy against A. gracilis at 0.2 mg L(-1); however, none of the treatments controlled P. kewesis.
• Lemna minor was the most sensitive non-target organism, while Hyphressobrycon eques was the least sensitive.

Conclusions:

• Copper-based algaecides are highly effective for controlling the unicellular alga A. gracilis.
• Diquat also shows promise for A. gracilis control, but efficacy against filamentous algae like P. kewesis is limited.
• Careful consideration of non-target organism sensitivity, particularly L. minor, is essential when applying these algaecides.