Hormetic dose-response of halogenated organic pollutants on Microcystis aeruginosa: Joint toxic action and mechanism

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 .…”

“…In another example, one-week-long singular exposures of M. aeruginosa to the polycyclic aromatic hydrocarbons phenanthrene and benzo­[α]­pyrene and their mixture revealed growth hormesis at ≤1000 μg L –1 phenanthrene and at ≤279 μg L –1 mixture, whereas singular benzo­[α]­pyrene significantly inhibited growth at all tested concentrations (≥200 μg L –1 ) . Concurrent contaminants may even produce additive or synergistic effects on the low-dose hormetic stimulation of microcystins and growth, indicating magnified hazards and risks. ,, Thus, the issue of contaminant-induced hormesis in such cyanobacteria becomes more pressing because mixture effects are commonly neglected in ecological risk assessments.…”

“…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. For example, the cell density of M. aeruginosa significantly increased by the singular antibiotics ciprofloxacin and sulfamethoxazole and their combination at 0.05–0.2, 0.1–0.2, and 0.02–0.1 μg L –1 , respectively, after 8 days of exposure .…”