CHANGES IN YIELD IN IN-VIVO FLUORESCENCE OF CHLOROPHYLL A AS A TOOL FOR SELECTIVE HERBICIDE MONITORING

Triazines and derivatives of phenylurea, which are often found in outd oor water samples, induce specific changes in the yield of the in-vivo chlorophyll a-fluorescence of PSII. These changes are correlated quan titatively with the concentration of the herbicides and can therefore be used to set-up a low-price monitor system. In order to detect selec tively the herbicide-sensitive part of the fluorescence emission e bio assay system was optimised with respect to a pulse amplitude modulated fluorimeter was used. The test organism, growing and measuring condit ions. ale relationship between fluorescence yield and herbicide concen trations were experimentally determin:d for the triazines atrazine and simazine and the phenylurea herbicide DCMU and mathematically fitted (r=0.99). The I-50-values were 0.9 mu M for DCMU, 2.2 mu M for simazin e and 3.3 mu M for atrazine. The detection limit of about 0.5 mu M cle arly 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 hop e to combine this fluorometric bioassay with a potent herbicide precon centration method like a solid-phase extraction procedure.