Toxicity of Tetracycline and Metronidazole in Chlorella pyrenoidosa
Antibiotics have become a new kind of organic pollutant as they are widely used in the water environment of China. Tetracycline (TC) is a class of broad-spectrum antibiotics produced or semi-synthesized by actinomycetes. Metronidazole (MTZ) is the first generation of typical nitroimidazoles. The content of nitroimidazoles is relatively high in medical wastewater, and their ecotoxicity is worthy of attention because they are difficult to completely eliminate. In this paper, the effects of TC and MTZ on the growth, cell morphology, extracellular polymer and oxidative stress ofChlorella pyrenoidosa(C. pyrenoidosa) were studied, and the toxic interactions between TC and MTZ mixture components were analyzed. The results showed that the 96h-EC50of TC and MTZ was 8.72 mg/L and 45.125 mg/L, respectively. The toxicity of TC toC. pyrenoidosawas higher than that of MTZ, and the combined toxicity effect of TC and MTZ was synergistic after the combined action of a 1:1 toxicity ratio. In addition, the algal cells ofC. pyrenoidosadied to varying degrees, the membrane permeability of algal cells was increased, the membrane was damaged, the surface of algal cells exposed to higher concentration of pollutants was wrinkled, and their morphology was changed. The extracellular polymer ofC. pyrenoidosawas affected by a change in concentration. The effect of pollutants on the reactive oxygen species (ROS) level and malondialdehyde (MDA) content ofC. pyrenoidosaalso had an obvious dose–effect relationship. This study contributes to the assessment of the possible ecological risks to green algae due to the presence of TC and MTZ in aquatic environments.Keywords:tetracycline;metronidazole;Chlorella pyrenoidosa;single toxicity;combined toxicity
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