Blue-green algae, or cyanobacteria—arguably the most widespread, abundant and ancient organisms on earth—can produce a toxin called BMAA, which is linked with neurodegenerative disorders such as Alzheimer's and an illness in Guam similar to Lou Gehrig's and Parkinson's diseases. An international team examined cyanobacteria living in marine, brackish and freshwater environments throughout the world along with those living symbiotically with plants and lichens.

Ninety percent of the 41 strains studied generated BMAA, and at the right times or growth conditions all cyanobacteria might produce the toxin, the investigators report in the April 5 Proceedings of the National Academy of Sciences USA. The toxin appeared in samples of Baltic Sea and oceanic cyanobacteria blooms, suggesting the microbes could be releasing significant quantities of BMAA. As water pollution and global temperatures rise and trigger blooms, which can cover thousands of square kilometers, the health consequences could prove of increasing concern, the scientists say.