Risk to human health associated with the environmental occurrence of cyanobacterial neurotoxic alkaloids anatoxins and saxitoxins

Abstract

Cyanobacteria are ubiquitous photosynthetic micro-organisms forming blooms and scums in surface water; among them some species can produce cyanotoxins giving rise to some concern for human health and animal life. To date, more than 65 cyanobacterial neurotoxins have been described, of which the most studied are the groups of anatoxins and saxitoxins (STXs), comprising many different variants. In freshwaters, the hepatotoxic microcystins represent the most frequently detected cyanotoxin: on this basis, it could appear that neurotoxins are less relevant, but the low frequency of detection may partially reflect an a priori choice of target analytes, the low method sensitivity and the lack of certified standards. Cyanobacterial neurotoxins target cholinergic synapses or voltage-gated ion channels, blocking skeletal and respiratory muscles, thus leading to death by respiratory failure. This review reports and analyzes the available literature data on environmental occurrence of cyanobacterial neurotoxic alkaloids, namely anatoxins and STXs, their biosynthesis, toxicology and epidemiology, derivation of guidance values and action limits. These data are used as the basis to assess the risk posed to human health, identify critical exposure scenarios and highlight the major data gaps and research needs.

Keywords:

• Cyanobacteria
• cyanotoxins
• human health
• neurotoxins
• toxicological risk assessment

Acknowledgements

The authors wish to thank the three anonymous reviewers, who provided useful suggestions and comments, addressing the quality of the manuscript which was substantially improved.

Declaration of interest

The authors declare that the paper was prepared as part of their normal duties with no external funding and that none of them have appeared in any regulatory or legal proceedings related to the subject matter of the review. The conclusions drawn are exclusively those of the authors and not necessarily those of Istituto Superiore di Sanità. The authors’ affiliations are as shown on the cover page.

Notes

1. Ciguatera Fish Poisoning is characterized by a number of clinical symptoms beginning with gastrointestinal disorders 3–6 h after eating contaminated food followed by neurological disorders in the next 6 h.

2. The new nomenclature is cited at the beginning of the paragraph, although elsewhere the names reported in the original papers are used.

3. Ciguatera-like symptoms in humans include gastrointestinal (nausea, vomiting, and diarrhea), neurological (headaches, muscle aches, paresthesia, numbness, ataxia, vertigo, hallucinations) and/or cardiovascular effects. Recover is generally slow and symptoms can last from days to months.

4. The action levels are the maximum concentration of ATX in edible sport fish and shellfish tissues that a typical consumer (one meal per week) could ingest without exceeding the reference doses (RfDs). For higher consumption rates, the action level is divided by the average number of meals consumed each week.

5. The mouse unit is defined as the amount of injected toxin which would kill a 20 g mouse in 15 minutes.