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 yield of microalgae in order to detect photosystem II specific herbicides in outdoor water samples. The system was tested with respect to sensitivity and reliability with two species: Chlorella fusca (a green alga) and Phaeodactylum tricornutum (a diatom). The main advantages are the use of cell cultures without preliminary centrifugation, the evaluation of variable fluorescence from steady-state levels, and the rapidity of the measurement. Concentrations around the binding constant of inhibitors (around 10(-8) M) can be detected for dichlorophenlydimethylurea, atrazine and simazine. The new system was compared with the commercially available pulse amplitude fluorometer PAM 101; it was shown that the sensitivity was about 10 times greater than with PAM 101, working at optimal chlorophyll concentrations. The advantages and limits of both systems when applied to free-water samples are discussed.