Influences of the micropollutant erythromycin on cyanobacteria treatment with potassium permanganate

Abstract

Cyanobacteria blooms and micropollutants (e.g., antibiotics) in source waters are two increasing environmental issues worldwide. This study hypothesized that the coexisting antibiotics may possibly alter the efficiency of water treatment processes through affecting the physiological and biochemical characteristics of cyanobacterial cells. A toxic strain of Microcystis aeruginosa was exposed to the common antibiotic erythromycin (ERY) at environmentally relevant concentrations; then, samples were collected on days 1, 4 and 6 to assess the efficiency of potassium permanganate (KMnO 4) in cyanobacteria oxidation. The percentage of intact cells remained constant after treatment with 2 mg L-1 KMnO 4 in M. aeruginosa samples dosed with 0-5.0 μg L-1 ERY. Although 6 mg L-1 KMnO 4 could damage cyanobacterial cells, its ability was considerably reduced as the concentrations of ERY increased. KMnO 4 oxidation degraded the intracellular microcystins (MCs) in all of the cyanobacterial samples, even the samples with intact cells, possibly resulting from the stimulation of intracellular reactive oxygen species (ROS). The highest amounts of total MCs remained after oxidation with 2 and 6 mg L-1 KMnO 4 in 0.2 μg L-1 ERY-treated cyanobacterial samples, which may be due to large amounts of MC production. The 5.0 μg L-1 ERY inhibited the growth of cyanobacterial cells and downregulated the expression of the MC synthesis gene (mcyB), which resulted in the lowest amounts of total MCs. However, it led to the highest concentration (4.6 μg L-1) of extracellular MCs after treatment with 2 mg L-1 KMnO 4 for 300 min. Generally, this study indicates that the effectiveness of KMnO 4 oxidation in cyanobacteria treatment decreased when the concentration of ERY increased. Hence, the possible risks caused by the coexistence of cyanobacteria and antibiotics, such as reduced efficiency of water treatment processes in cyanobacteria inactivation and degradation of the dissolved MCs, need to be taken into account.