A novel approach for phytotoxicity assessment by CCD fluorescence imaging.

Rapidity, cost effectiveness, ecological reliability, and the possibility of the direct interpretation of bioassay results are the main motivations for the development of new approaches in ecotoxicity testing. Color, turbidity, and nutrient content are factors of great importance in phytotoxicity testing of natural samples. Some algal bioassay end points are markedly influenced by such factors or are impossible to estimate in their presence. An algal toxicity test applicable as an early-warning system has to be able to give a signal in the shortest time possible (hours). We used CCD fluorescence imaging to evaluate toxicity effects in algae, cyanobacteria, and vascular plants, and the data were compared with standard end points. Plant physiologists use this device mainly for photosynthesis research, but common photosynthetic parameters used to characterize chlorophyll fluorescence (F(v)/F(m), F(0), and F(m)) or its quenching (NPQ) have only limited ecotoxicological applicability. Previously published estimations based on the geometrical complement to measured data (complementary area) in the fast kinetics (Kautsky effect) respond especially to pollutants affecting electron transport in the PSII. We recommend using a definite integral value combined with relative fluorescence decay (Rfd) to obtain a sensitive and fast toxicity response. Our approach integrates more mechanisms of toxicity (effects on membranes, proton pump, ATP synthesis, etc.) and improves the toxicity signal, which is more ecotoxicologically relevant. This method can give results after 2-6 h of exposure and is especially useful as an early-warning system and for the toxicity assessment of environmental samples with unknown nutrient status. Results with our approach after 4-6 h are comparable with those obtained with a 96-h standard algal assay. A similar methodical approach can be applied for toxicity evaluation of plants or lichens, or for in situ ecotoxicological studies of microphytobenthos communities.