Comparison of Partitioning and Efficacy Between Copper Algaecide Formulations: Refining the Critical Burden Concept

Filamentous mat-forming algae are increasingly impairing freshwater resources. To restore water utility, reactive management programs often involve application of copper-based algaecides. Copper algaecide formulations can differ significantly, and this research outlined an advanced approach to evaluate formulation efficiency for controlling filamentous algae. Two common algal species (Lyngbya wollei, Pithophora varia) were used to assess copper internalization and adsorption as well as relation to control among copper formulations. CaptainA (R) XTR achieved control (7-day EC85) of L. wollei with internal copper concentrations of 0.78 and 0.76 mg Cu/g based on chlorophyll a content or filament viability, respectively. CutrineA (R) Ultra achieved control of L. wollei based on filament viability only at 0.85 mg Cu/g. Internalized copper concentrations required for control following Captain XTR exposures were similar for P. varia, 0.81 and 0.95 mg Cu/g, whereas Cutrine Ultra and copper sulfate did not elicit control nor attain the critical internal copper threshold. The relationship between internalized copper and responses, among all formulations, was significant (P < 0.0001) with R-2 values of 0.920 and 0.935 for L. wollei and 0.807 and 0.826 for P. varia based on filament viability and chlorophyll a content, respectively. Formulation efficiency, internalized copper versus total amended, was greatest with Captain XTR (average 0.17), followed by Cutrine Ultra (0.13), and copper sulfate (0.09). By measuring the efficiency of a specific algaecide and the corresponding amount required to achieve control of targeted algal biomass, management objectives can be achieved while decreasing environmental loads of copper, number of treatments, and operational costs.