A pulse amplitude modulated fluorometer (PAM) was used to measure the chlorophyll fluorescence induction kinetics (OIDP). The increase of I level, recorded at two different excitation light intensities, was used to monitor atrazine, simazine, diuron and isoproturon. The methods used were applied to a, sensitive chlorophyte, Selenastrum capricornutum. Concentrations of about 0.01 mu M of diuron, 0.04 mu M of isoproturon and atrazine and 0.08 mu M of simazine can be detected significantly. I-50-values obtained by the most sensitive method, corresponding to an excitation light intensity of 130 mu mol photon . m(-2) . sec(-1), are 0.3 mu M for atrazine, 0.5 mu M for simazine, 0.05 mu M for diuron and 0.2 mu M for isoproturon. The inhibition of S. capricornutum growth over a 4 days period was also studied and the I-50 obtained were about 0.4 mu M for-triazines, 0.03 mu M for diuron and 0.2 mu M for isoproturon.
