Blooms of toxic microorganisms in aquatic environments: marine microalgae and freshwater cyanobacteria. A brief review with a particular focus on the Italian situation: Diffusion and health effects of toxic marine microalgae and freshwater cyanobacteria in Italy

In marine and freshwater environments, many species of primary producers (microalgae and cyanobacteria) can synthesize biotoxins, which are harmful to other organisms including humans. Other species are dangerous just for the large amount of biomass they produce during bloom (for the consequent depletion of oxygen, suffocation of other organisms, deterioration of beaches, etc.) with significant economic damages. The proliferations of all these species are defined Harmful Algal Blooms (HAB). The majority of marine and estuarine HABs are algae (eukaryotes), while cyanobacteria (prokaryotes) are responsible for blooms in freshwater environments. Toxin-producing organisms have a significant health impact, as human population can be exposed to toxins through the oral route, by ingestion of contaminated food, by accidental ingestion of contaminated water during bathing and recreational activities and by ingestion of contaminated drinking water. Humans are also exposed through inhalation of aerosols, and through direct contact with contaminated water or microorganisms. In the last 40 years a significant worldwide increase in the number of toxic blooms, toxic species and known toxins has been acknowledged, but there is still no general consensus on the causes. Many countries have implemented monitoring plans to control their blooms and to prevent humans from dangerous exposure. After a brief description of the major health effects worldwide, the state of the art on marine and freshwater species in Italy is described and major research needs are highlighted.