Aquatic Toxicology 74 (2005) 150–159 Determination of photosynthetic and enzymatic biomarkers sensitivity used to evaluate toxic effects of copper and fludioxonil in alga Scenedesmus obliquus David Dewez a , Laure Geoffroy b , Guy Vernet b , Radovan Popovic a,∗ a D´ epartement de Chimie et de Biochimie, Centre TOXEN, Universit´ e du Qu´ ebec ` a Montr´ eal, CP 8888, Succursale Centre-Ville, Montr´ eal, Qu´ ebec, Canada H3C 3P8 b Laboratoire d’Eco-Toxicologie, Unit´ e de recherche “Vignes et Vins de Champagne”, UPRES-EA 2069, Universit´ e de Reims Champagne-Ardenne BP 1039, F51687 REIMS CEDEX 2, France Received 9 July 2004; received in revised form 29 December 2004; accepted 18 May 2005 Abstract Modulated PAM fluorometry and Plant Efficiency Analyser methods were used to investigate photosynthetic fluorescence parameters of alga Scenedesmus obliquus exposed to inhibitory effect of fungicides copper sulphate and fludioxonil (N-(4- nitrophenyl)-N ′ -propyl-uree). The change of those parameters were studied when alga S. obliquus have been exposed during 48 h to different concentrations of fungicides (1, 2 and 3 mg l -1 ). Under the same condition, enzymatic activities of catalase, ascorbate peroxidase, glutathione reductase and glutathione S-transferase were investigated to evaluate antioxidative response to fungicides effects. The change of sensitivity of those parameters was dependent to the mode of fungicide action, their concentration and time of exposure. For copper effects, the most indicative photosynthetic biomarkers were parameters Q N as non-photochemical fluorescence quenching, Q Emax as the proton induced fluorescence quenching and ABS/RC as the antenna size per photosystem II reaction center. Copper induced oxidative stress was indicated by increased activity of catalase serving as the most sensitive and valuable enzymatic biomarker. On the other hand, fludioxonil effect on photosynthetic parameters was very negligible and consequently not very useful as biomarkers. However, fludioxonil induced strong antioxidative activities associated with cytosol enzymes, as we found for catalase, ascorbate peroxidase and glutathione S-transferase activities. By obtained results, we may suggest for the activation of those enzymes to be sensitive and valuable biomarkers of oxidative stress induced by fludioxonil. Determination of biomarkers sensitivity may offer advantages in providing real criteria to use them for ecotoxicological diagnostic studies. © 2005 Elsevier B.V. All rights reserved. Keywords: Copper; Fludioxonil; Scenedesmus obliquus; Biomarkers; Photosynthesis; Fluorescence ∗ Corresponding author. Tel.: +1 514 987 3000x8467; fax: +1 514 987 4054. E-mail address: popovic.radovan@uqam.ca (R. Popovic). 1. Introduction Copper sulphate and fludioxonil (N-(4-nitrophe- nyl)-N ′ -propyl-uree) are commonly used as fungicides 0166-445X/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2005.05.007