Journal of Applied Phycology 5: 505-516, 1993. © 1993 Kluwer Academic Publishers. Printed in Belgium. 505 Changes in yield of in-vivo fluorescence of chlorophyll a as a tool for selective herbicide monitoring Roswitha Conrad', Claudia Bilchel', Christian Wilhelml ' *, Wafa Arsalane 2 , Claire Berkaloff 2 & Jean-Claude Duval 2 Institut far A llgemeine Botanik, Johannes Gutenberg- Universitiit Mainz, D-55099 Mainz, Germany; 2 Ecole Normale Superieure, 46, Rue d'Ulm, F-75231 Paris, France (*author for correspondence) Received 6 May 1993; accepted 22 June 1993 Key words: fluorescence, bioassay, PSII herbicides, algae, triazines, phenylureas Abstract Triazines and derivatives of phenylurea, which are often found in outdoor water samples, induce spe- cific changes in the yield of the in-vivo chlorophyll a-fluorescence of PSII. These changes are correlated quantitatively with the concentration of the herbicides and can therefore be used to set-up a low-price monitor system. In order to detect selectively the herbicide-sensitive part of the fluorescence emission a pulse amplitude modulated fluorimeter was used. The bioassay system was optimised with respect to test organism, growing and measuring conditions. The relationship between fluorescence yield and herbicide concentrations were experimentally determined for the triazines atrazine and simazine and the phenylurea herbicide DCMU and mathematically fitted (r= 0.99). The I 50 -values were 0.9 MM for DCMU, 2.2 MaM for simazine and 3.3 /M for atrazine. The detection limit of about 0.5 MM clearly shows that the sensitivity of this bioassay system is too low to reach the requirements of the drinking water regulation. However, due to its insensitivity against complex water matrices, there is good hope to combine this fluorometric bioassay with a potent herbicide preconcentration method like a solid-phase extraction procedure. Abbreviations: Chl, chlorophyll; DCMU, dichlorophenyldimethylurea, F, fluorescence, Fm, maximal fluo- rescence; Fo, minimal fluorescence; Fv, variable fluorescence; GC, gas chromatography; HPLC, High performance liquid chromatography; MS, mass spectroscopy; PAM, pulse-amplitude-modulated fluor- ometer; PSII, photosystem II; qN, non-photochemical quenching; 150, concentration required for 50% inhibition of electron transport; CCCP, carbonyl cyanide m-chlorophenylhydrazon Introduction chromatography (HPLC), both coupled with a preconcentration step, are used for the sensitive According to the German drinking water regula- detection of a pesticide pollution (Oehmichen tion (1986), the sum of all pesticides in drinking etal., 1987; Granet etal., 1988; Schlett, 1991; water must not exceed 0.5 pg 1-. Usually, gas Reupert etal., 1992). However, the chemical chromatography (GC) or high performance liquid analysis of a water sample is expensive and very