Abstract
Cyanobacteria harmful algal blooms (cHABs) are associated with a widerange of adverse health effects that stem mostly from the presence ofcyanotoxins. To help protect against these impacts, several healthadvisory levels have been set for some toxins. In particular, one of themore common toxins, microcystin-LR, has several advisory levels set fordrinking water and recreational use. However, compared to other waterquality measures, field measurements of microcystin-LR are not commonlyavailable due to cost and advanced understanding required to interpretresults. Addressing these issues will take time and resources. Thus,there is utility in finding indicators of microcystin-LR that arealready widely available, can be estimated quickly and in situ, and usedas a first defense against high concentrations of microcystin-LR.Chlorophyll a is commonly measured, can be estimated insitu, and has been shown to be positively associated withmicrocystin-LR. In this paper, we use this association to provideestimates of chlorophyll a concentrations that are indicative ofa higher probability of exceeding select health advisory concentrationsfor microcystin-LR. Using the 2007 National Lakes Assessment and aconditional probability approach, we identify chlorophyll aconcentrations that are more likely than not to be associated with anexceedance of a microcystin-LR health advisory level. We look at therecent US EPA health advisories for drinking water as well as the WorldHealth Organization levels for drinking water and recreational use andidentify a range of chlorophyll a thresholds. A 50% chance ofexceeding one of the microcystin-LRadvisory concentrations of0.3, 1, 1.6, and 2 g/L is associated with chlorophyll aconcentration thresholds of 23.4, 67.0, 83.5, and 105.8, respectively.When managing for these various microcystin-LR levels, exceeding thesereported chlorophyll a concentrations should be a trigger for further testing and possible management action.
Highlights
IntroductionNumerous events and legislative activities have raised the public awareness of harmful algal blooms[1,2,3]
Over the last decade, numerous events and legislative activities have raised the public awareness of harmful algal blooms[1,2,3]
Comments: (1) In discussing the lake exceedances of the various recommended levels by EPA, the addition of ‘drinking water’ is appropriate in my opinion. It is mentioned earlier in the methods, further providing the information in the results is helpful to a novice reader or a person just becoming familiar with drinking water regulations and guidelines, as the U.S EPA child level may be presumed by a reader to be a level for recreation in a lake rather than a level associated with finished drinking water after water treatment. (2) “All lakes had reported chl a concentrations that exceeded detection limits” Does this mean that some were over range? Or does this mean that “All lakes had detectable levels of chl a”
Summary
Numerous events and legislative activities have raised the public awareness of harmful algal blooms[1,2,3]. The World Health Organization (WHO) has proposed microcystin advisory levels for drinking water and a range of recreational risk levels[7,8]. While these levels and associated advisories are likely to help mitigate the impacts from harmful algal blooms, they are not without complications. One of these complications is that they rely on available measurements of microcystin-LR. While laboratory testing (e.g., chromatography) remains the gold standard for quantifying microcystin-LR concentrations in water samples, several field test kits have been developed. Each technique requires nuanced understanding of the detection method (e.g., limit of detection, specific microcystin variants being measured, and sampling protocol)
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