Abstract
Cyanobacteria harmful algal blooms (cHABs) are associated with a wide range of adverse health effects that stem mostly from the presence of cyanotoxins. To help protect against these impacts, several health advisory levels have been set for some toxins. In particular, one of the more common toxins, microcystin, has several advisory levels set for drinking water and recreational use. However, compared to other water quality measures, field measurements of microcystin are not commonly available due to cost and advanced understanding required to interpret results. Addressing these issues will take time and resources. Thus, there is utility in finding indicators of microcystin that are already widely available, can be estimated quickly and in situ, and used as a first defense against high levels of microcystin. Chlorophyll a is commonly measured, can be estimated in situ, and has been shown to be positively associated with microcystin. In this paper, we use this association to provide estimates of chlorophyll a concentrations that are indicative of a higher probability of exceeding select health advisory concentrations for microcystin. Using the 2007 National Lakes Assessment and a conditional probability approach, we identify chlorophyll a concentrations that are more likely than not to be associated with an exceedance of a microcystin health advisory level. We look at the recent US EPA health advisories for drinking water as well as the World Health Organization levels for drinking water and recreational use and identify a range of chlorophyll a thresholds. A 50% chance of exceeding one of the specific advisory microcystin concentrations of 0.3, 1, 1.6, and 2 μg/L is associated with chlorophyll aconcentration thresholds of 23, 68, 84, and 104 μg/L, respectively. When managing for these various microcystin levels, exceeding these reported chlorophyll aconcentrations should be a trigger for further testing and possible management action.
Highlights
Over the last decade, numerous events and legislative activities have raised the public awareness of harmful algal blooms[1,2,3]
In their analysis they find that total nitrogen and chlorophyll a show the strongest association with microcystin. They identify chlorophyll a and total nitrogen concentrations that are associated with exceeding 1 μg/L of microcystin. These findings suggest that chlorophyll a concentrations could track the new US Environmental Protection Agency (USEPA) microcystin health advisory levels for drinking water
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 microcystin advisory levels for drinking water and for 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. While laboratory testing (e.g., chromatography) remains the gold standard for quantifying microcystin 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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