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(PW033) A QSAR for the photoinduced toxicity of PAHs to plants and bacteria is predictive for Daphnia magna.
Lampi, M.1, Gurska, Y.1, Huang, X.-D.1, Dixon, D.1, Greenberg, B.1, 1 Department of Biology, University of Waterloo, Waterloo, ON, Canada
ABSTRACT- Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants known for their photoinduced toxicity. The characteristic chemical structure of PAHs consists of conjugated orbitals, facilitating absorption of light in the UV/far blue region of the solar spectrum. Upon absorption of a photon, photoinduced toxicity of PAHs is manifested through two mechanisms: photosensitization, and photomodification. The photosensitized production of highly reactive singlet oxygen has been widely studied as a major mechanism of photoinduced toxicity. PAH photomodification, generally through photooxidation, results in a wide array of products, many of which are more toxic than the parent compound. Both are known to occur at environmentally relevant levels of solar radiation in aquatic systems. An empirical model predicted the photoinduced toxicity of 16 PAHs in Lemna gibba. This QSAR model showed that a photosensitization factor (PSF) and a photomodification factor (PMF) could be additively combined to accurately describe photoinduced toxicity. This model was subsequently found to correlate well with toxicity to the luminescent bacterium Vibrio fischeri. To further validate this model, it was necessary to determine whether it is predictive in other organisms of ecotoxicological importance. Daphnia magna was chosen as the next model organism. Toxicity was assessed as LT50 for immobility, and assays were performed under simulated solar radiation. As with both L. gibba and V. fischeri, neither the PSF nor the PMF demonstrated great correlation to toxicity to D. magna individually. However, a PSF modified for D. magna did in fact exhibit correlation with toxicity (r2 = 0.716), which was further improved (r2 = 0.846) when summed with a modified PMF. This data provides further evidence that this model, which was developed based on the assumption of a bipartite mechanism of PAH phototoxicity, is applicable across a broad range of species of interest.
Key words: photoinduced toxicity, QSAR, PAHs, Daphnia magna
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