Individual and combined toxicity of sulfamethoxazole and desethylatrazine to Chlorella vulgaris: growth inhibition, photosynthetic activity and oxidative stress

ABSTRACT The influence of emerging contaminants on the composition of aquatic ecosystems, including antibiotics and pesticide metabolites, is receiving increasing attention. In this study, the acute and chronic toxic effects of single and combined exposure to sulfamethoxazole (SMX) and desethylatrazine (DEA) on Chlorella vulgaris (C. vulgaris) were evaluated in terms of growth, pigment content and antioxidant systems. The findings demonstrated that cytochrome content and cell growth followed a similar trend for both single and combined exposures, with C. vulgaris being affected in a dose-dependent manner, and chlorophyll content decreasing at high exposures. For SMX and DEA, the maximum inhibition rates at a single exposure were 95.14% and 87.31%, respectively. Cell membrane permeability, superoxide dismutase content and catalase release were significantly increased in the early stages of cultivation. Additionally, cell density was used to calculate the single exposure half effect concentration (EC50), which was then used as part of the toxic unit (TU) method for evaluating mixture interactions. TU analysis revealed that the interaction between SMX and DEA shifted from being synergistic to being antagonistic after 7 d of incubation. These results suggest that SMX and DEA may play a significant role in aquatic ecosystems. GRAPHICAL ABSTRACT