Toxic responses and antioxidative enzymes activity of Scenedesmus obliquus exposed to fenhexamid and atrazine, alone and in mixture

• Toxic effects of atrazine and fenhexamid on microalgae, S. obliquus, were studied.
• Fenhexamid induced antioxidative enzyme activities at different concentrations.
• Antioxidative enzyme activities are good biomarkers of atrazine exposure in microalgae.

Laboratory studies were conducted to determine the effects of different concentrations of fenhexamid and atrazine (25, 50 and 100 µg L−1) on growth and oxidative stress on Scenedesmus obliquus (microalgae) after exposure for 24, 48, and 96 h. In addition, residues of fenhexamid and atrazine were determined in the culture medium after 96 h; 52%, 44% and 43% of fenhexamid remained in the medium for the lowest, middle and highest concentrations, respectively. Atrazine concentration decreased significantly in the medium with time. The reduction was faster with the lowest concentration (−53%), than in the highest concentration (−46%), while it was intermediate with 50 µg L−1 (−47%). The antioxidative enzyme activities were used as biomarkers to evaluate the toxic effects of fenhexamid and atrazine on the microalgae. Enzymatic activities were measured in the presence of each compound alone after 24, 48 and 96 h and also in mixture after 24 h exposure. The results showed that fenhexamid and atrazine induced antioxidative enzyme activities (GST, CAT and GR) at different concentrations. Catalase activities (CAT) in both pesticides treated-algae were significantly increased. Additionally, an increase in gulathione-S-transferase (GST) was observed in algae after 24, 48 and 96 h of exposure to both fenhexamid and atrazine. Antioxidative enzymes in fenhexamid and atrazine mixture treatment showed an antagonistic interaction after 24 h of exposure in algae.