M7 PM Metals in the Environment: Aquatic Biological Perspectives
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 327-329

(GRE-1117-816574) Assessment of mixture toxicity of metals, PAHs and oxyPAHs to Daphnia magna: Synergistic toxicity via ROS.

Xie, F¹, Koziar, S¹, Lampi, M¹, Dixon, D¹, Norwood, W², Borgmann, U², Huang, X¹, Greenberg, B¹, ¹ Department of Biology, University of Waterloo, Waterloo, ON, Canada² Environment Canada, National Water Research Institute, Burlington, ON, Canada

ABSTRACT- Metals, polycyclic aromatic hydrocarbons (PAHs) and their derivatives are commonly present in complex mixtures in the environment. Strikingly, little is known about mixture toxicity and specific mechanisms of mixture toxicity. Cu, Ni and Cd were selected, representing a highly redox-active, a moderately redox-active and a non-redox active metal, respectively. We have found synergistic effects for the combinations of Cu or Ni with phenanthrenequinone (PHQ), a major photoproduct of phenanthrene (PHe). In contrast, additive toxicity was observed in mixtures of Cd plus PHQ, as well as in mixtures of Cu plus PHE. The increased toxicity of Cu plus PHQ is physiologically based because assimilation of Cu was similar with or without PHQ. We have shown using the dichlorofluorescein (DCF) fluorescence assay that Cu and Ni alone induce ROS formation in D. magna, whereas PHQ and Cd had no effect on ROS production. Relative to the individual metals, enhanced ROS production was observed in D. magna treated with mixtures of Cu plus PHQ, and Ni plus PHQ, but not with Cd plus PHQ mixtures. Furthermore, the increased toxicity and RIS production were attenuated by the antioxidants L-ascorbic acid, beta-carotene or dimethylthiourea (DMTU). The results indicate that there are potential toxic interactions between redox-active metals and modified PAHs, and provide evidence for a ROS-mediated mechanism for mixture toxicity.

Key words: modified PAHs, metals, reactive oxygen species (ROS), antioxidants