Community succession during the preventive control of cyanobacterial bloom by hydrogen peroxide in an aquatic microcosm

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 .…”

“…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.…”

“…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%. − ,…”

“…We estimated the average stimulation of the production ability or concentration of microcystins by low, sub-NOAEL doses of contaminants at 57.9% of the control value (95% CI estimated at 53.7–62.1%, n = 203 dose responses). − ,,− ,− ,− , This stimulation was induced by contaminant concentrations on average 280.9 μg L –1 (95% CI estimated at 146.9–414.8 μg L –1 , n = 203 dose responses). − ,,− ,− ,− , Low doses enhancing production of microcystins are even 100–20000 times smaller than the lowest toxic concentrations inhibiting algal growth and production of microcystins. ,,,, Among the 203 dose responses analyzed, 93.6% were induced by concentrations ≤100 μg L –1 , while the majority (67.5%) of the dose responses were induced by concentrations ≤10 μg L –1 . As many as 60.6% of the dose responses were induced by concentrations as little as ≤0.6 μg L –1 .…”