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Introduction
Cyanobacterial blooms remain a global burden, due to the production of cyanotoxins (1). An outbreak of cyanobacterial blooms induces the release of microcystins (MCs) into water, and is a serious threat to aquatic organisms, wildlife and humans that ingest the toxins from cyanobacteria or water aquatic ecosystems (2). MCs are a group of >100 cyanobacterial toxin variants, of which MC-LR is the most common variant and the most potently toxic peptide (3). Furthermore, it has previously been reported that MC-LR is highly hepatotoxic and is a liver tumor-specific promoter (4).
MCs are a group of highly stable environmental pollutants that are not readily hydrolyzed or oxidized at normal pH, thus, they may survive for months to several years (5). Toxins released into the water from broken algal cells are a threat to human health through skin contact, inhalation, hemodialyses and oral ingestion. It has been reported that MCs may cause damage to the respiratory system (6); however, the associated mechanism has yet to be elucidated. Incidents involving poisoning of the respiratory system have been reported in several countries and regions as a result of contact with poisonous algae since the 20th century (7–9). In 1916, respiratory system symptoms were reported in patients following algal poisoning on the West Coast of Florida in the United States (8). Furthermore, in Britain in 1989, pneumonia was detected in patients after direct contact with MCs-contaminated water as a result of swimming or boating (7,9). Toxic cyanobacteria present in water entertainment parks can also generate atomized microcystins that enter the respiratory tract, which is the predominant route leading to disease of the respiratory system (10). Pilotto et al (11) reported that participants exposed to >5,000 cyanobacteria cells/ml for >1 h had a significant increase in flu-like symptoms, such as fever and skin rashes, as compared with unexposed participants over the course of 7 days (11). In lakes with a high concentration of cyanobacteria (cell surface area >12.0 mm2/ml), the probability of individuals developing respiratory symptoms is 2.1 times that of individuals who are exposed to a low concentration of cyanobacteria (cell surface area <2.4 mm2/ml) (12). Water-based recreational activities can expose participants to low concentrations of microcystins via the aerosol; Backer et al (13)...