Stormwater Irrigation Volume II: Cyanobacteria Counts with Toxin Concentrations in Stormwater Ponds and After Biofiltration to Reduce Health Risks (2006)
The second phase of the research on stromwater reuse by the Stormwater Management Academy. This report summarizes information on the levels of total and potentially toxin Cyanobacteria and the Microcystin toxins that may be present in stormwater ponds. It also examines the potential reduction of these constituents by sand filtration so that the stormwater can be reused for nonpotable purposes.
Algal blooms are a common occurrence in water bodies of all shapes and sizes in the State of Florida as well as all other locations around the world. Cyanobacteria, or blue-green algae, have proven to be of special concern due to proliferation and potential to produce toxins that are harmful to humans, livestock and wildlife. Casual observations of lakes and stormwater ponds in Florida will confirm algal conditions in many. The health risks and the potential for exposure to harmful and possibly fatal toxins associated with these algal blooms are becoming more evident as more nutrients are discharged to our waters.
Data on the counts of Cyanobacteria have been previously reported for large lakes and rivers in the State of Florida, but no studies have been performed regarding stormwater ponds. Since stormwater ponds along roadways and in residential neighborhoods may be a source for irrigation, research to document the occurrence of the algae and their toxins is warranted due to the potential health effects associated with Cyanobacteria.
Fourteen ponds in central Florida were sampled for total and potentially toxin Cyanobacteria and the Microcystin Toxins. These ponds represent different land uses and were chosen because of the visual appearance of Cyanobacteria and in three cases, previously laboratory identified but not quantified levels of Cyanobacteria. Cyanobacteria were found to be in all the stormwater ponds of various sizes associated with watersheds in the central Florida area. Even though the algae and its associated toxins were encountered in the stormwater ponds evaluated for this study, the levels detected were much lower than the values discovered in previous studies performed in the larger lakes and rivers around the State.
The removals of the algae and their toxins were evaluated using a commonly occurring poorly graded sandy soil with construction characteristics common to “A-3” soils. Filtration through 4 feet of the soil using waters from three of the ponds in the study noted removals of the algae and a reduction in the toxins.
The World Health Organization has established a drinking water standard for Cyanobacteria Toxins at 1 ug/L. There is no standard for aerosol levels, and in fact only minor problems health problems have been reported when exposure to aerosols was studied. Of the twenty-eight stormwater pond water samples, two exceeded the drinking water standard. While none of the filtrate samples exceeded the limit. Filtration will help in attenuating the toxin concentrations.