An Assessment of Potential Threats to Human Health from Algae Blooms in the Indian River Lagoon (USA) 2018–2021: Unique Patterns of Cytotoxicity Associated with Toxins

The Indian River Lagoon (IRL), a 156-mile-long estuary located on the eastern coast of
Florida, experiences phytoplankton bloom events due to increased seasonal temperatures coupled
with anthropogenic impacts. This study aimed to gather data on the toxicity to human cells and
to identify secondary metabolites found in water samples collected in the IRL. Water samples
from 20 sites of the IRL were collected during the wet and dry seasons over a three-year period.
A panel of cell lines was used to test cytotoxicity. Hemagglutination, hemolysis, and inhibition
of protein phosphatase 2A (PP2A) were also measured. Cytotoxic blooms were seen both in the
south (Microcystis) and the north (Pyrodinium) of the IRL. Each toxin induced a consistent pattern
of cytotoxicity in the panel of human cell lines assayed. During blooms, cytotoxicity due to a
single type of toxin is obvious from this pattern. In the absence of blooms, the cytotoxicity seen
reflected either a mixture of toxins or it was caused by an unidentified toxin. These observations
suggest that other toxins with the potential to be harmful to human health may be present in the
IRL. Moreover, the presence of toxins in the IRL is not always associated with blooms of known
toxin-producing organisms.