Physiological and biochemical responses of the freshwater green algae Closterium ehrenbergii to the common disinfectant chlorine

•Toxic effects of biocide chlorine on freshwater green algae Closterium ehrenbergii.•Significant reduction in growth and pigment level of C. ehrenbergii exposed above 0.5 mg L−1 Cl2.•Cl2 causes damage to the photosystem observed by chlorophyll autofluorescence.•Significant increases of antioxidant enzymes activities (LPX, SOD, CAT and GSH) with increasing Cl2.•Cl2 discharged in aquatic environments damages to C. ehrenbergii & other microalgae.

Chlorine (Cl2) is widely used as a disinfectant in water treatment plants and for cleaning swimming pools; it is finally discharged into aquatic environments, possibly causing damage to the non-target organisms in the receiving water bodies. Present study evaluated the effects of the biocide Cl2 to the green alga Closterium ehrenbergii (C. ehrenbergii). Growth rate, chlorophyll a levels, carotenoids, chlorophyll autofluorescence, and antioxidant enzymes were monitored up to 72-h after Cl2 exposure. C. ehrenbergii showed dose-dependent decrease in growth rate and cell division after exposure to Cl2. By using cell counts, the median effective concentration (EC50)−72-h was calculated to be 0.071 mg L−1. Cl2 significantly decreased the pigment levels and chlorophyll autofluorescence intensity, indicating that the photosystem was damaged in C. ehrenbergii. In addition, it increased the production of reactive oxygen species (ROS) in the cells. This stressor significantly increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase, and glutathione, and affected the physiology of the cells. These results indicate that Cl2 induces oxidative stress in the cellular metabolic process and leads to physiological and biochemical damages in the green algae. Cl2 discharged in industrial effluents and from water treatment plants may cause harmful effects to the C. ehrenbergii a common freshwater microalgae and other non-target organisms.