Effects of different algaecides on the photosynthetic capacity, cell integrity and microcystin-LR release of Microcystis aeruginosa

Bench scale tests were conducted to study the effects of four common algaecides, including copper sulfate, hydrogen peroxide, diuron and ethyl 2-methylacetoacetate (EMA) on the photosynthetic capacity, cell integrity and microcystin-LR (MC-LR) release of Microcystis aeruginosa. The release of potassium (K+) from cell membrane during algaecide exposure was also analyzed. The three typical photosynthetic parameters, including the effective quantum yield (φe), photosynthetic efficiency (α) and maximal electron transport rate (rETRmax), were measured by a pulse amplitude modulated (PAM) fluorometry. Results showed that the photosynthetic capacity was all inhibited by the four algaecides, to different degrees, by limiting the energy capture in photosynthesis, and blocking the electron transfer chain in primary reaction. For example, at high diuron concentration (7.5 mg L−1), φe, α and rETRmax decreased from 0.46 to 0.19 (p < 0.01), from 0.20 to 0.01 (p < 0.01) μmol electrons m−2 s−1/μmol photons m−2 s−1, and from 160.7 to 0.1 (p < 0.001) μmol m−2 s−1 compared with the control group after 96 h of exposure, respectively. Furthermore, the increase of algaecide dose could lead to the cell lysis, as well as release of intracellular MC-LR that enhanced the accumulation of extracellular MC-LR. The order of MC-LR release potential for the four algaecides was CuSO4 > H2O2 > diuron > EMA. Highlights: • PAM was used to investigate the effects of algaecides on Microcystis aeruginosa. • We estimate the release of potassium (K+) from cell membrane for cell lysis. • The risk of microcystin-LR release was evaluated after algaecides exposure. • The order of MC-LR release potential was copper sulfate > hydrogen peroxide > diuron > ethyl 2-methylacetoacetate