Detection of harmful bioactive compounds produced by bloom-forming pelagic algae is important to assess the potential risks to communities. We applied two cell-based assays, an erythrocyte lysis assay (ELA) that assesses membrane integrity, and a RTgill-W1 cytotoxicity assay (RCA) that detects changes in cell metabolism, to evaluate the cytotoxic effects of: (1) individual toxins and noxious compounds; and (2) complex mixtures of compounds produced by cyanobacteria and chrysophyte isolates. ELA was insensitive to toxins and noxious compounds except at exceptionally high concentrations (EC50≥106 nM). RCA was sensitive to noxious compounds only, at concentrations greater than reported environmental averages (EC50≥103 nM). Cultured isolates produced bioactive compounds that had recognizable, dose dependent, toxic effects. Toxicity of these bioactive compounds depended on the taxa (cyanobacteria, not chrysophytes), growth stage (stationary phase more toxic than exponential phase), location (intracellular more toxic than extracellular), and iron status (iron-replete cells more toxic that iron-deplete cells)
