Bull. Environm. Contam. Toxicol. 24,562-569 (1980) Interactions between the Solvent Acetone and the Pyrethroid Insecticide Permethrin on Activities of the Blue-Green Alga Anabaena Glenn W. Stratton, Robert E. Burrell, M. Lynn Kurp, and Charles T. Corke Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2Wl The effect of pesticides on non-target organisms is an area of intensive research. Since many pesticides have low water sol- ubility, they are often dissolved in an organic solvent prior to addition into experimental systems. The use of solvents in biol- ogical experiments necessitates the inclusion of solvent controls and the adaptation of a standard solvent concentration for routine use. However, there is little consensus among researchers as to which level of solvent is suitable for any given kifld of exper- iment and little is known about the effects of solvents on biol- ogical systems. The possibility that the solvent interacts with the test compound is ignored. It is possible that one level of solvent may affect the overall response elicited by a chemical, while another concentration of the same solvent would not. Acetone, a common solvent, is known to inhibit the replica- tion of vaccinia and rabbitpox viruses (GHENDON and SAMOILOVA 1968, CHERNOS et al. 1972), the radial growth of fungi (R.E. BURRELL and C.T. CORKE, submitted paper), and is lethal to rain- bow trout (MAJEWSKI et al. 1978). Acetone can both stimulate, and inhibit, the production of aflatoxins in Aspergillus, depend- ing on the concentration used (BENNETT et al. 1976). Acetone was found to have no significant effect on wood-rotting fungi (BEZEMER et al. 1973). In this study the effect of acetone on photosynthesis and nitrogen fixation by three species of the blue-green alga, Anabaena, and the interactions of acetone on the toxicity of the pyrethroid insecticide, permethrin, (3-phenoxybenzyl-3-(2,2- dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate) were stud- ied. Anabaena is an important freshwater blue-green alga (FOGG 1971). 0007-4861/80/0024-0562 $01.60 9 1980 Springer-Verlag New York Inc.