HABs: What are they and how do we measure?

Algae can be problematic in water when they grow in abundance, because when these blooms die, their degradation in the environment can deplete oxygen dissolved in water, killing fish, crabs, and oysters.  Harmful Algal Bloom (HABs) got a lot of attention over the summer of 2019. In large part, this was due to the death of three dogs in North Carolina, which were later identified to have swum in a lake that contained a cyanobacterial bloom.  Cyanobacteria are free-living photosynthetic bacteria, and when they ‘bloom’, are known for vivid, blue-green colors in both freshwater and marine environments.  While they are an important foundation of the world’s oceans, they are also thought to have oxygenated our planet from a toxic atmosphere to the air we breathe today. 

But they also produce different classes of toxins that are so potent, they can have adverse health effects in concentrations of parts per billion!  And that has been just one part of the challenge with assessing water quality during bloom events: these compounds require special instrumentation and has largely been confined to academic institutions until recently. 

First, there isn’t a gold standard where researchers are using the same method to measure these compounds, some studies have utilized high-performance liquid chromatography (HPLC), Liquid chromatography–mass spectrometry (LC-MS), and enzyme linked immunosorbent assay (ELISA) which have differences in precision and accuracy between the methods.  Utilizing these methods are quite costly, and can quickly exhaust funding to obtain a sufficient sample size required of routine monitoring.  Second, monitoring Lake Pontchartrain, which is a large water body at 630 square miles, can be prohibitively expensive to sample enough to account for spatial variability, or the differences that could be measured at various sampling sites.

It would be great if we could use another measure of water quality to predict the concentration of cyanobacterial toxins in water. One great new tool that has emerged is the Harmful Algal Bloom Monitoring System, a satellite remote sensing application developed by the National Oceanic and Atmospheric Administration.  Unfortunately, the amount of cyanobacterial-derived toxins and cyanobacteria are independent of each other. That is, cyanobacterial toxins can be absent in large blooms, and similarly, toxins can persist in the environment after the dissipation of a bloom.  So, using remote sensing tools alone to estimate the concentrations of cyanotoxins are insufficient. 

Prior to May 2019, it was also difficult to understand the implications of cyanotoxins that were measured in recreational waters.  How dangerous is it to measure 9 parts per billion in a water? How is it different from a sample that measures 5 parts per billion? The US Environmental Protection Agency published water quality criteria and swimming advisory values last summer, which established recommended water concentrations at microcystins (8 micrograms per liter) and cylindrospermopsin (15 micrograms per liter).  These values are calculated on the assumption that should a small child accidently ingest a volume of water, the ingested amount of cyanotoxins will not have an adverse health effect.  Should a water sample exceed the calculated concentrations, EPA recommends issuing a swimming advisory.

There are still a number of unknowns: we have limited understanding of the genetics that regulate the production of these toxins, much less the dynamics of cyanobacteria and cyanotoxins within our basin.  Fortunately, we did not measure cyanotoxins in samples during the summer of 2019 that exceeded the EPA criteria.