Rapid effects of diverse toxic water pollutants on chlorophyll a fluorescence: Variable responses among freshwater microalgae

► Algal chlorophyll fluorescence Fv/Fm declines within minutes with toxin exposure. ► Fv/Fm suppression shows dose-dependence (Km are nanomolar range for PSII inhibitors). ► Fv/Fm suppression also shows concentration-dependence to toxins KCN and glyphosate. ► Effects of toxic pollutants can be effectively and rapidly detected using algal Fv/Fm. ► Field testing of natural communities will be complicated by taxon-specific responses.