Effective Early Treatment of Exponential Growth and Microcystin Production with Hydrogen Peroxide and Hydroxyapatite.

Mitigating cyanotoxin production is essential to protecting aquatic ecosystems and public health. However, current harmful cyanobacterial bloom (HCB) control strategies have significant shortcomings. Because predicting HCBs is difficult, current HCB control strategies are employed when heavy HCBs have already occurred. Our pilot study developed an effective HCB prediction approach that is employed before exponential cyanobacterial growth and massive cyanotoxin production can occur. We used a quantitative polymerase chain reaction (qPCR) assay targeting the toxin-encoding gene to signal the timing of treatment. When control measures were applied at an early growth stage or one week before the exponential growth of (predicted by qPCR signals), both hydrogen peroxide (HO) and the adsorbent hydroxyapatite (HAP) effectively stopped growth and microcystin (MC) production. Treatment with either HO (10 mg·L) or HAP (40 µm particles at 2.5 g·L) significantly reduced both gene copies and MC levels compared with the control in a dose-dependent manner. While both treatments reduced MC levels similarly, HAP showed a greater ability to reduce gene abundance. Under laboratory culture conditions, HO and HAP also prevented MC production when applied at the early stages of the bloom when gene abundance was below 10 copies·mL.