Analysis of Algaecide Exposures: an Evaluation of the I3 − Method to Measure Sodium Carbonate Peroxyhydrate Algaecides

Abstract

Algaecides are commonly used to control noxious algal growths in water resources. In order to make accurate predictions about responses of target and non-target species to algaecide exposures, reliable methods are needed to confirm exposures in the laboratory and the field. The focus of this research was to evaluate the I3− method for measuring hydrogen peroxide (H2O2) exposures associated with applications of a sodium carbonate peroxyhydrate (SCP)-based algaecide. To meet this overall objective, method detection limits, interferences from field waters (turbidity, color, and algal cell density), and storage stability of samples were measured. The method detection limits were 0.2 (p < 0.0001) and 0.25 mg H2O2/L (p = 0.0002) for laboratory and field waters, respectively. The upper method detection limit was 7.5 mg H2O2/L for both waters. Turbidity (25.3 NTU) and color of field-collected water did not interfere with measurements. Algal cell densities of 104, 105, and 106 cells/mL of two planktonic algal species in laboratory water did not interfere with measurements. Measurements of samples stored in dark refrigeration and on ice remained stable over 4 days, while measurements of samples stored in direct sunlight in ambient temperatures were altered after 1 day. The I3− method accurately measured H2O2 exposures in the laboratory water, field water, and laboratory water containing planktonic algae used in this experiment within the range of concentrations that would be applied in a field setting. These data demonstrated that this method has utility for confirming exposures after laboratory and field treatments of SCP-based algaecides.