TOXIC RESPONSES AND CATALASE ACTIVITY OF LEMNA-MINOR L. EXPOSED TO FOLPET, COPPER, AND THEIR COMBINATION

Toxicity of copper and folpet-two fungicides widely used on grape-was evaluated on Lemna minor L., a sensitive aquatic weed regularly used f or (eco)toxicological studies. Toxicity assessments were based on inhi bition of growth and chlorophyll content of L. minor cultures after 7 days. IC10, IC50, and IC90 were determined for both compounds alone an d were respectively, 0.03, 0.16, and 0.95 mg liter(-1) for copper and 1.20, 7.50, and >40 mg liter(-1) for folpet. When both compounds were combined, the response oft. minor depended on the initial folpet conce ntration, Indeed, a slight synergy was observed for 5 mg liter(-1) fol pet, while at folpet concentrations of 20 to 35 mg liter(-1), the two fungicides were antagonists, The antagonism was positively correlated with folpet concentration. Antagonism between Cu and folpet could not be explained by a reduced bioavailability of Cu since concentration of free copper in the mixture did not depend on the presence of folpet, One physiological defense response elicited by copper in plants is an increase in catalase activity. Copper and folpet stimulated catalase a ctivity and changes in the activity of the enzyme could not account fo r the synergy but possibly for the antagonism. Nevertheless, catalase activity increased significantly after a 24-h exposure to 25 mu g lite r(-1) of copper, The use of this property as a rapid and sensitive bio marker to monitor the toxicity of xenobiotics alone or in combination and of environmental water is discussed. (C) 1998 Academic Press.