A NEW FLUOROMETRIC DEVICE TO MEASURE THE IN-VIVO CHLOROPHYLL-A FLUORESCENCE YIELD IN MICROALGAE AND ITS USE AS A HERBICIDE MONITOR

A new fluorometric device was developed to measure the fluorescence yi eld of microalgae in order to detect photosystem II specific herbicide s in outdoor water samples. The system was tested with respect to sens itivity and reliability with two species: Chlorella fusca (a green alg a) and Phaeodactylum tricornutum (a diatom). The main advantages are t he use of cell cultures without preliminary centrifugation, the evalua tion of variable fluorescence from steady-state levels, and the rapidi ty of the measurement. Concentrations around the binding constant of i nhibitors (around 10(-8) M) can be detected for dichlorophenlydimethyl urea, atrazine and simazine. The new system was compared with the comm ercially available pulse amplitude fluorometer PAM 101; it was shown t hat the sensitivity was about 10 times greater than with PAM 101, work ing at optimal chlorophyll concentrations. The advantages and limits o f both systems when applied to free-water samples are discussed.