Human activity, endotoxins, and water quality during a cyanobacteria bloom at a recreational beach
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The presence of cyanobacteria blooms (CHABs) may interfere with recreational activities. Endotoxins can occur with CHABs and at high concentrations in air, endotoxins can elicit respiratory illness. We characterized human activity and environmental attributes of a recreational beach impacted by a CHAB and evaluated air and water endotoxin concentrations.
We monitored a single site at an inland lake for ten weekend days in California during summer/fall 2017. We monitored water quality three times daily including: endotoxins, cyanotoxins, phytoplankton cell counts, phycology, chlorophyll-a, phycocyanin, dissolved oxygen, pH, and temperature. We recorded daily weather and air: temperature, humidity, and endotoxin activity. We recorded human activity hourly by age group in, on, and near the water. We t-tested mean numbers of people recreating by categories of endotoxin exposure. We developed two multivariable linear models, one for air, and one for water endotoxin outcomes.
The CHAB was dominated by a Synechocystis spp. bloom. Mean phytoplankton counts (SD) were 351,359 (76090) cells/mL. Microcystin concentrations were all above the LOD of 0.15 ng/mL, mean (SD) = 0.33(0.07) ng/mL. Mean (SD) endotoxin in water and air were 358.11 (140.42) EU/mL, and 4.8 (6.6) EU/m3, respectively. Water endotoxin concentrations were significantly and positively associated with microcystin concentrations, controlling for sample time, water temperature, pH, humidity, chlorophyll-a, and phytoplankton cell count. No covariate remained statistically significant in association with air endotoxin concentrations in a multivariable model. We observed significantly more teenagers recreating on the beach during low air endotoxin study days; no other significant differences among human activity categories by endotoxin category were observed.
Endotoxins in water were positively associated with microcystin concentrations. This finding to deserves further investigation. All air endotoxin concentrations were below irritant thresholds and our highest measured concentrations (18 EU/m3) would not be expected to deter recreational activities. This abstract does not reflect EPA policy.