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Earth and Oceanographic Science

Cyanotoxins as human health hazards: beyond neurodegeneration

Geoffrey A. Codd, College of Life Sciences, University of Dundee, DD1 5EH, UK and School of Biological and Environmental Sciences, University of Stirling, FK9 4LA, UK.

Awareness and risk management plans among health-care professionals, and those in the drinking water supply, recreational water, crop irrigation and aquaculture sectors, of cyanobacterial mass populations and cyanotoxins toxins, are essential to protect human health from these hazards. On several occasions, an earlier lack of awareness and protective measures was followed by human illnesses and deaths. Considerable progress has occurred in communication to end-users and decision-makers about the health risks presented, however, this need continues as the number of recognized cyanotoxins increases, and as understanding of their toxicity via exposure media and routes develops. Emerging cyanotoxins requiring further human health risk assessment include the neurotoxins BMAA (β-N-methylamino-L-alanine) and DAB (α-γ-diaminobutyric acid). Continuing reports of cyanobacterial cell extract toxicities in bioassays, which lack or have been cleared of known cyanotoxins , indicate that further cyanotoxins remain to be identified. This emphasises the continuing need for bioassays to complement physicochemical methods in cyanotoxin discovery and characterisation.

Risk assessment has proceeded along classical lines where effects and levels of exposure, to individual toxins or toxin families, particularly the microcystins of which over 90 structural variants are known, are characterized and estimated. This has led to policies for environmental monitoring, intervention thresholds, and guidelines at state, federal and international level, with corresponding legislation in several countries beyond the USA. The microcystins, though long-recognized as hepatotoxins and tumor-promoters, are now receiving attention as potential, additional neuro- and genotoxins. Whilst risk assessment of individual cyanotoxins continues to be necessary, cyanotoxins do not typically occur in isolation, but in combination with other cyanotoxins (e.g. BMAA plus microcystins, nodularins, anatoxins, cylindrospermopsins, lipopolysaccharide endotoxins), and also with other environmental health hazards (microbial pathogens, metals, physiological stressors et c). Risk assessment of multiple exposures to such multiple insults, including cyanotoxins, is required.