Single antibiotics and their mixture at environmentally relevant concentrations may disrupt the physiology of A....

Antibiotics are common pollutants in freshwater ecosystems that can pose a threat to non-target organisms. This represents a serious risk, as antibiotics may affect primary producers, including green algae. In this study, we investigated the influence of three antibiotics and their mixture at environmentally relevant concentrations: chloramphenicol (360 ng L^-1), streptomycin (100 ng L^-1), and sulfamethoxazole (213 ng L^-1) on green algae Acutodesmus obliquus. After 10 days of algal exposure to antibiotics separately and in the mixture, selected parameters were studied. Chloramphenicol caused a decrease in algal growth rate, cells size and ratio of the variable to maximum fluorescence. Streptomycin disrupted only cell size distribution. Sulfamethoxazole decreased growth rate, cells size and caused lower levels of chlorophylls and carotenoids. The mixture of antibiotics altered the biggest number of physiological parameters: it decreased the growth rate, cells size and led to lower levels of chlorophyll a, chlorophyll a/b ratio, while boosting the respiration rate. This may indicate that a cumulative effect of pharmaceuticals had occurred. Photosynthetic activity and lipid peroxidation status remained unchanged compared to the control. Antibiotics at environmentally relevant concentrations can affect A. obliquus physiology. The uniqueness of this study lies in assessing cumulative effects and prolonged exposure.