WP9 Pesticide Mixtures
Wednesday, 16 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(SUN-1117-767696) Responses of non-target species to two algaecides and an adjuvant used to control Lyngbya wollei.

Sundberg, S¹, Jones, R¹, Rodgers, Jr., J¹, ¹ Clemson University, Clemson, SC, USA

ABSTRACT- Two algaecides (Algimycin PWF® and PAK-27™) and an adjuvant (Cide-Kick II®) have been used to control the nuisance algal species, Lyngbya wollei, in Lay Lake and Lake Jordon, Alabama. Information regarding the comparative toxicities of these products is essential for assessing potential risks or adverse effects to non-target species. The objectives of this study were: 1) to measure the relative toxicities and potencies of Algimycin PWF, PAK-27, and Cide-Kick II to a vertebrate, Pimephales promelas Rafinesque, and two invertebrates, Hyalella azteca Saussure and Daphnia magna Straus, in static, non-renewal, short-term (96-hr) aqueous and sediment laboratory exposures with survival as the measured endpoint, and 2) to measure the relative toxicities and potencies of mixtures of the two algaecides and adjuvant as they were applied in the Alabama reservoirs. Three replicate test chambers (250-mL beakers), 10 juvenile organisms each, were used for each concentration tested and a control for all experiments using site water. Test chamber temperature was maintained at 25±1^oC in a temperature-controlled incubator with a light:dark photoperiod of 16hr:8hr. Water characteristics including dissolved oxygen, pH, hardness, alkalinity, and conductivity were measured throughout exposure experiments. Relative toxicities (NOECs and LOECs) of each algaecide, adjuvant, and mixture were calculated based on organism survival using analysis of variance (ANOVA, alpha = 0.05). Lethal concentrations (LC₅₀s) of algaecides and/or adjuvant were calculated using the Spearman-Karber method. Estimated aqueous LC₅₀s for PAK-27 were above the targeted concentration of 6.21 mg/L in Lay Lake for treatment of L. wollei, whereas estimated aqueous LC₅₀s for Cide-Kick II were much lower than the targeted concentration of 5 ml/L. However, the presence of sediment in the test chambers helped to alleviate toxicity to organisms. Results from this research provide essential information regarding the risks to non-target species involved in treating L. wollei with these products in these Alabama reservoirs.

Key words: algaecides, lyngbya, non-target species