Microcystin and BMAA toxicity compared to bloom density in South Florida cyanobacterial harmful algal blooms

Harmful algal blooms (HABs) have significant negative impacts on communities and economies along coasts, both marine and freshwater, where the proliferation of algae producing toxins poses a public health concern. In freshwater lakes and rivers across the United States blooms of Microcystis and other cyanobacteria have been found to produce a range of toxins, the most abundant and best studied being microcystin. In addition to this class of hepatotoxins different strains of cyanobacterial HABs have been found to produce a range of other identified and some as yet unidentified toxins. One of the more recently discovered toxins produced by cyanobacteria is beta-N-methylamino-L-alanine (BMAA), which is a modified amino acid that has been linked neurodegenerative diseases including early onset Alzheimer’s, Amytrophic Lateral Sclerosis, and Parkinson’s. Cyanobacterial HABs have occurred with some regularity and sometimes great intensity in densely populated areas across the US, including the Great Lakes and South Florida. In these areas exposure to cyanotoxins including microcystin and BMAA is an important public concern, however the relationship between HAB density and HAB toxicity is not well-defined, and furthermore the expected relative abundance of different toxins—each with different health impacts—has not been established. To assess the relationship between HAB density and HAB toxicity, as well as investigate the relative ratio of different toxins, we collected samples of cyanobacterial HABs across South Florida, from Lake Okeechobee, down the Caloosahatchee river, and into the estuarine environment of Cape Coral. Samples were collected at five to nine sites on three different days across the intense HAB events that occurred in 2018. Water samples were filtered to collect particulate material that was extracted for microcystin and BMAA, with concentrations quantified by liquid chromatography triple quadrupole mass spectrometry. HAB density was assessed by chlorophyll concentration and cell counts by flow cytometry. Across the sites and days sampled we found a consistent relationship between chlorophyll concentration and toxin concentration, as well as a consistent relationship between microcystin concentration and BMAA concentration.