Review of Cyanobacterial Neurotoxins—Information for Prioritizing Future Science Directions

Science Center Objects

The current state of knowledge on the modes of action, production, fate, and occurrence of the freshwater cyanobacterial neurotoxins, anatoxin-a and saxitoxin, was reviewed and synthesized to identify gaps and critical research needs to better understand the health effects of algal toxins.

Toxins produced by cyanobacteria in freshwater systems can adversely affect wildlife, domestic animals, and human health. Cyanotoxins are classified into three main groups based on the organ system they can affect: dermatoxins (skin), hepatotoxins (liver), and neurotoxins (nervous system). The most frequently studied freshwater cyanotoxins are the microcystins, which are hepatotoxins; however, the neurotoxins anatoxin-a and saxitoxin also have been linked to acute animal poisonings and are understudied in freshwater environments.  


Image: Aphanizomenon Flos-aquae Under the Microscope

Aphanizomenon is a common bloom-forming cyanobacteria, AKA, blue-green algae.  Many strains produce saxitoxin and cylindrospermopsin. (Credit: Barry H. Rosen, Public domain.)

To fill this knowledge gap, the U.S. Geological Survey (USGS), along with academic partners, completed a review of laboratory and field studies worldwide that examines the modes of action, production, fate, and occurrence of the freshwater neurotoxins anatoxin-a and saxitoxin. Their research identified 41 anatoxin-a producing species and 15 saxitoxin-producing species of freshwater cyanobacteria. Studies were reviewed that detected anatoxin-a and saxitoxin on every continent except Antarctica.


The review collates information from numerous publications into one comprehensive resource. This resource provides information on gaps in knowledge, including understanding why these neurotoxins are produced, what happens to them once they are released into the environment, their primary and secondary exposure routes, how their presence changes on time scales ranging from hours to years, and sublethal health effects on individual organisms and populations. 


This review provides information to help scientists prioritize future research on anatoxin-a, saxitoxin, and other cyanotoxins to address health concerns related to toxin exposures. USGS research on algal toxins is continuing through the Toxins and Harmful Algal Blooms Science Team.

The Environmental Health Program (Contaminants Biology and Toxic Substances Hydrology) of the U.S. Geological Survey Ecosystems Mission Area supported this study.