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1H c (2) - Pharmaceuticals (TH6/3) Phytotoxicity of Antibiotics and Antibiotic-Containing Mixtures to Aquatic Macrophytes in Laboratory Studies and Aquatic Microcosms. Brain, Richard1, Johnson, David1, Sanderson, Hans1, Wilson, Christian1, Hanson, Mark1, Mabury, Scott2, Sibley, Paul1, Solomon, Keith1, 1 University of Guelph, Guelph, Ontario, Canada2 University of Toronto, Toronto, Ontario, Canada ABSTRACT- Antibiotics are known to have antichloroplastic properties, yet, their effects on aquatic higher plants are largely unknown. Antibiotics are the primary group of medical substances investigated for environmental impacts as a result of their extensive use in both, human therapy and animal husbandry, easily detectible effect endpoints, and greater probability for introduction into the environment. In laboratory screening assays with Lemna gibba, fluoroquinolone, sulfonamide and tetracycline antibiotics have shown the greatest phytotoxic potency out of the twelve different classes of antibiotics assessed. To further quantify the effects of antibiotics and antibiotic-containing mixtures on aquatic macrophytes, microcosm and laboratory experiments were conducted with several pharmaceutical compounds, singularly and in combination. Two pharmaceutical studies were conducted in 12000 L microcosms during the summer of 2002. These studies included an eight pharmaceutical mixture (50 day) with five treatments and a singular macrolide antibiotic study (35 day) with seven treatments. Several growth and pigment endpoints were measured in the test species L. gibba, Myriophyllum sibiricum and Myriophyllum spicatum. In the eight pharmaceutical mixture growth endpoints were significantly inhibited in M. sibiricum, particularly root number, and all endpoints were significantly inhibited in L. gibba plants. Levofloxacin and sulfamethoxazole have been implicated as the phytotoxic agents in this mixture as supported by laboratory studies with L. gibba. In the second microcosm study the macrolide antibiotic tylosin was found to significantly increase several endpoints in L. gibba and M. spicatum, especially growth endpoints. Laboratory screening assays with mixtures of antibiotics and herbicides commonly found in agricultural runoff, including tetracyclines, suflonamides, atrazine, and glyphosate, revealed additive phytotoxic potency in L. gibba at low Key words: macrophytes, antibiotics, microcosms, mixtures |
g/L concentrations. The underlying biochemical mechanisms of toxicity will also be further discussed.