Hydrogen peroxide, an ecofriendly remediation method for controllingMicrocystis aeruginosatoxic blooms

In February 2017, aMicrocystis aeruginosabloom (maximum 55 mu g L(-1)chlaand microcystin concentration of 40 mu g L-1) occurred in a freshwater pond in Padre Island National Seashore (PINS), TX, USA, causing mortality of migratory redhead ducks and local animals. To treat the pond without further damage to the ecosystem, we proposed the use of H2O2. A nomograph of H(2)O(2)required for oxidizing different initial cyanobacterial biomass levels to achieve desired final microcystin and chlaconcentration was developed. With a chlaconcentration > 50 mu g L-1, the nomograph predicted > 97% removal efficiency when 50 mg L(-1)peroxide was used. Then, an outdoor mesocosm experiment with four treatment levels (0, 10, 50 mg L(-1)H(2)O(2)and 10 mg L(-1)H(2)O(2)with ultrasonication) was tested. In the mesocosm experiment, discrete samples were assessed for cell morphology, pigment, and microcystin toxin content (n = 3) at six different time intervals during the 48-h treatment period. Cell morphology was affected after 4-h exposure at 50 mg L-1 H(2)O(2)treatment. Overall, > 75% of microcystin and > 80% of chlawere destroyed after 48-h exposure to 50 mg L-1 H2O2. The pond was treated with 10 mg L-1 H(2)O(2)which reduced chlaby 60% and microcystin by 35% after 2 days. Control of the cyanobacterial bloom using H(2)O(2)was effective in lab and mesocosm experiments, but the cyanobacterial bloom recovered at PINS 2 weeks after the treatment. The recovery resulted from an insufficient H(2)O(2)addition, identifying a need to re-evaluate current protocols. Overall, no residual H(2)O(2)were detected in any scales of treatment.