Comparative toxicity of rac- and S-tebuconazole to Daphnia magna

Abstract

Tebuconazole is a chiral triazole fungicide used as raceme in a variety of agricultural applications. Earlier studies showed that tebuconazole is toxic to many non-target aquatic organisms but relative data for tebuconazole enantiomers are lacking. Thus, goal of this study was to evaluate and compare the toxicity of rac- and S-tebuconazole with Daphnia magna at both acute and chronic levels according to Organization for Economic Cooperation and Development (OECD) guidelines 202 and 211 respectively, to provide some guidelines for optimizing chiral pesticides application and management. The exposure concentrations were 0.1, 0.5, 1, 2, 4, 8, 10 mg L⁻¹ for both rac- and S-tebuconazole and their 48-h EC₅₀ values to D. magna were 3.53 (3.32–3.78) and 2.74 (2.33–3.10) mg L⁻¹ respectively, indicating that these both are medium toxic to D. magna with no significant toxicity difference at acute level. In chronic test, <24-h old D. magna were exposed to 0.01, 0.05, 0.10, 0.20, and 0.40 mg L⁻¹ of rac- and S-tebuconazole with one blank and one solvent control for 21 days according to OECD guideline 211. Four developmental (molting rate, days to the 1st and 3rd brood, and body length) and five reproductive (size of the 1st and 3rd brood, number of broods, and number of neonates) parameters for each D. magna were determined. Results showed that both rac- and S-tebuconazole significantly reduced the reproduction and impacted the development of D. magna at concentrations of 0.05 mg L⁻¹ or higher. Furthermore, S-tebuconazole was more toxic than raceme, and the difference between effects on the same parameters induced by rac- and S-tebuconazole was statistically significant. These results demonstrated that the chronic toxicity of S-tebuconazole might be underestimated in general use, and further studies should focus more on the biological behaviors of enantiomers and not just the raceme of tebuconazole and other chiral pesticides in the environment.

Keywords:

• Rac-tebuconazole
• S-tebuconazole
• Daphnia magna
• toxicity

Acknowledgments

We thank Dr. Shirong Gao in the Chinese Academy of Protection Medicine Science for providing the test organisms, and also thank Dr. Jinling Diao (Department of Applied Chemistry, China Agricultural University) and Stephen R. Lantz (Department of Environmental Science, Policy and Management, University of California at Berkeley) for many nutritious advices on writing the manuscript.

Funding

The present study was financially supported by National Twelfth Five-Year Plan for Science and Technology (Grant No. 2011BAE06B09) and Special Fund for Agro-Scientific Research in the Public Interest: Study on Comprehensive Cultivation Techniques for Pesticide Risk Assessment (Project No. 200903054-02).