Effect of hydrogen peroxide on microcystin-LR from Microcystis sp

Microcystis spp. blooms in fish ponds can lead to fluctuations in water parameters, and the microcystin-LR (MC-LR) toxin they produce may pose health risks for fish, as well as consumers. Hydrogen peroxide (H2O2) treatment has been demonstrated to reduce populations of Microcystis spp. in aquaculture ponds. This study conducted 2 trials to investigate whether these treatments result in the release of MC-LR under laboratory conditions. We applied 7 mg l-1 of H2O2 to a Microcystis sp. culture and assessed the MC-LR level post-treatment. In the first trial, no MC-LR was detected in the H2O2 treatment group nor the negative control group, while 0.933 ± 0.381 ppb of MC-LR was extracted from 2344230 Microcystis sp. cells in 5 ml of media stock in our positive control group (where all cells were destroyed). In our second trial, where we added almost 30 times more Microcystis sp. to the culture media (i.e. 64125000 cells in 5 ml of stock), 19.333 ± 0.742 ppb of MC-LR were detected in the positive control on average. At this concentration of algae, our negative control (no treatment) and our H2O2 treatment group had 16.933 ± 0.303 ppb and 16.933 ± 0.109 ppb of MC-LR, respectively. The toxin levels were similar between the treated and untreated groups, but significantly less than the positive control group (p = 0.003). The results suggest that 7 mg l-1 H2O2 treatment to Microcystis sp. did not increase the level of MC-LR in the solution, but MC-LR was also not removed by the treatment. The low-dose 7 mg l-1 H2O2 treatment against Microcystis sp. bloom is unlikely to cause extra toxin (MC-LR) release to the medium.