A pulse-amplitude modulated fluorescence-based method for assessing the effects of photosystem II herbicides on freshwater periphyton

A test was developed that measures in vivo chlorophyll a fluorescence variables to assess the apparent sensitivity of freshwater periphytic algae to photosystem II inhibitors. Natural periphytic communities from rivers were collected on artificial substrata, and the effects of short-term exposures to two PSII herbicides (atrazine and isoproturon) on the fluorescence parameters were measured with a pulse-amplitude modulated fluorometer. The EC50 for each herbicide were calculated from fluorescence yield indices, and these results were compared to C-14-based primary production measurements on the same communities. The fluorescence-based method appears to give very reliable estimations of EC50 for each pesticide we tested, ranging from 0.46 to 5.18 muM and 0.07 to 6.77 muM for atrazine and isoproturon, respectively. This method could be used in ecotoxicology monitoring programs, to detect changes in natural periphyton populations sensitivity, following photosystem II herbicide contamination in rivers or lakes.