The use of pulse-amplitude modulated (PAM) fluorescence-based methods to evaluate effects of herbicides in microalgal systems of different complexity

Abstract

The herbicides isoproturon and atrazine were employed in microalgal bioassays of varying biological complexity: (i) Microalgal communities attached on surfaces (biofilms) were used for multi-species phytotoxicity assessment. (ii) The sensitivity of individual cells in intact biofilms was evaluated. (iii) Axenic cultures of Scenedesmus vacuolatus and Nitzschia palea were used for single species suspension bioassays. All three test approaches were based on the short-term inhibition of the photosynthetic quantum yield, evaluated by pulse-amplitude modulated (PAM)-fluorescence measurements by applying (i) a multi wavelength-excitation measuring device, (ii) a combination of a PAM-fluorometer with an epifluorescence microscope and (iii) a PAM-fluorometer for suspensions. The investigations revealed comparable sensitivity of all algal systems independent of their biological complexity. EC₅₀ values ranged from 0.008 to 0.11 mg L⁻¹ for isoproturon and 0.032–0.1 mg L⁻¹ for atrazine. Good correspondence of effect data was found for the same phyla in comparable test designs. The combination of the measuring systems revealed that the sensitivity of microalgae varies (i) between different algal phyla, (ii) in dependence to the toxicant applied and (iii) in accordance to the succession status of a biofilm community. The approaches used in this study provide improved tools for assessing ecological risks of PSII herbicides. The results of progressively complex experimental systems will allow extrapolation to realistic outdoor conditions where significantly complex communities of aquatic microalgae are exposed.

Keywords:

• Autotrophic biofilms
• community ecotoxicology
• Scenedesmus vacuolatus
• Nitzschia palea
• atrazine
• isoproturon
• Periphyton

Acknowledgements

We wish to acknowledge skillful support by I. Christmann, J. Krüger, A. Küster and M. Hönemann for technical assistance. Furthermore we would like to thank U. Schreiber and an anonymous reviewer for their helpful comments on the manuscript and P. Juneau for making this special issue possible. The financial support by the Commission of the European Community (Modelkey, SSPI-CT-2003-511237-2) is gratefully acknowledged.