W10 PM Environmental Interactions of Marine Antifoulants
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 341-342

(DEL-1117-564288) Mixture toxicity of the antifouling compound irgarol to the marine phytoplankton species Dunaliella tertiolecta..

DeLorenzo, M^{1, 2}, Serrano, L³, ¹ University of South Carolina, Columbia, SC, USA² NOAA/National Ocean Service, Charleston, SC, USA³ College of Charleston, Grice Marine Biology Program, Charleston, SC, USA

ABSTRACT- New antifouling compounds such as irgarol are being used to replace organotins on boat hulls, power plant intakes, and other marine applications. Irgarol is a triazine herbicide that works by inhibiting photosynthesis. Due to the prevalent use and persistence of irgarol in the estuarine environment, there is potential for nontarget effects on plants and algae. In coastal areas, irgarol is likely to be found in mixture with other commonly used pesticides. Decreases in phytoplankton population growth rates may impact nutrient cycling rates and food availability to higher trophic levels. Characterizing the toxicity of chemical mixtures likely to be encountered in the environment will improve ecological risk assessment capabilities. This study examined the toxicity of irgarol, individually and in mixture with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D) to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on D. tertiolecta cell density and population growth rate. Mixture toxicity was assessed using the toxic unit approach. Irgarol significantly inhibited Dunaliella tertiolecta cell density and growth rate. Cell density at 96 hours was significantly reduced at all concentrations compared to the control (LOEC = 0.03 g/L), whereas growth rate was significantly reduced at irgarol concentrations >0.09 g/L (LOEC = 0.27 g/L). Irgarol was significantly more toxic to D. tertiolecta than the other pesticides (irgarol 96h EC50 = 0.8 g/L; chlorothalonil 96h EC50 = 64 g/L; atrazine 96h EC50 = 59 g/L; 2,4-D 96h EC50 = 230 g/L). Interactive effects between irgarol and the other pesticides are described and concordance with the response addition mixture model is discussed.

Key words: marine antifoulant, mixture toxicity, phytoplankton, pesticides