Time- and dose-dependent allelopathic effects and mechanisms of kaempferol on toxigenic Microcystis growth

Low Levels of Contaminants Stimulate Harmful Algal Organisms and Enrich Their Toxins

“…This screening revealed eight additional papers. Thus, a total of 39 papers are included in this review, most of which include multifactorial experiments, such as different contaminants, strains, or additional experimental treatments other than contaminants. − …”

“…This review revealed numerous studies showing that various chemicals often induce hormesis in HAB-forming and toxin-producing cyanobacteria (blue-green algae), in particular, in different strains of Microcystis wesenbergii , and M . aeruginosa . ,,− ,,,− ,− , However, hormetic responses were also revealed in the neurotoxin-producing Anabaena flos-aquae and the bloom-forming haptophyte Prymnesium parvum , which produces the phycotoxin prymnesi . Such hormetic responses were further identified in Synechocystis sp., which may also contribute to bloom formation .…”

“…Hormetic responses of HAB-forming and toxin-producing cyanobacteria are induced by many chemicals, such as arsenate, , environmental estrogens, chlorinated organophosphorus flame retardants (Cl-OPFRs), halogenated organic compounds, heavy metals, hydrogen peroxide (algaecide), and the principal compound of yellow dye luteolin and other allelopathic chemicals/algaecides. ,− They were also induced by various antibiotics, ,,− ,,− nanomaterials, polycyclic aromatic hydrocarbons, rare earths, , and several pesticides and disinfectants. ,,,− Hence, hormetic responses represent a universal phenomenon across chemically diverse contaminants. The studies providing such evidence commonly apply environmentally relevant concentrations, demonstrating that realistic concentrations widely enhance harmful algae and the production of microcystins.…”

“…The hormesis-inducing contaminants include regulated pollutants (e.g., heavy metals) but also many unregulated global contaminants of emerging concern (not subject to regulation limiting their concentrations in the environment), such as various agrochemicals, nanomaterials, and pharmaceuticals. ,− ,,, This is of profound importance since sub-NOAEL stimulation of such HABs-forming and toxin-producing organisms cannot be captured by the traditional dose–response models. Importantly, multicomponent mixtures of the same or different (e.g., herbicide-antibiotics) types of contaminants widely induce hormesis in these cyanobacteria, which can persist in the presence of other costressors too. − ,,,,,− The presence of multiple contaminants can change the concentrations at which low-dose stimulation occurs.…”

“…As a result of the physiological hormetic controls (Figure ), cell density and proliferation, growth rate, as well as biomass exhibit hormetic responses to contaminants. ,− ,,− These hormetic responses appear generally across different stresses, highlighting that low, sub-NOAEL doses of contaminants can act in promoting the growth of the population of harmful algae, forming more robust, dense, and competitive colonies. The broad hormesis literature, including algae, demonstrates that the low-dose enhancement is restricted by the limits of biological plasticity. ,− Thus, the stimulation is modest in amplitude, typically, 30–60%, and rarely exceeding 100%, independently from the organisms, biological mechanisms, and stressors. ,− Similarly modest, but significant, are also the responses of chlorophylls, photosynthesis, and harmful algal growth/densities or proliferation to low doses of contaminants. − ,− ,,− , For instance, the stimulation of M. aeruginosa growth (cell density) by antibiotics was commonly less than 60% and as a rule smaller than 100%. − ,…”