Ref ID : 7010
Christopher P. Tatara, Michael C. Newman, John T. McCloskey, and Phillip L. Williams; Predicting relative metal toxicity with ion characteristics: Caenorhabditis elegans LC50. Aquatic Toxicology 39:279-290, 1997
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Quantitative Structure Activity Relationships (QSAR) predict relative toxicity of a family of chemicals from fundamental and surrogate molecular qualities. Most QSARs are developed for organic toxicants, with inorganic toxicants (metals) being under-represented. Successful predictive models for relative toxicity of divalent metal ions using ion characteristics have been produced using Microtox, a 15 min microbial bioassay. The present study extends this approach to longer exposure durations (24 hr), and a more complex organism (metazoan). Twenty-four hour LC50s (expressed as total metal concentration) for the free-living soil nematode, C. elegans were determined for Ca, Cd, Cu, Hg, Mg, Mn, Ni, Pb, and Zn in an aqueous medium. Relative metal toxicity was predicted with least squares linear regression and several ion characteristics. Toxicity was most effectively predicted ((r2)=0.89) with [logK(OH)] (where K(OH) is the first hydrolysis constant), which reflects a metal ion's tendency to bind to intermediate ligands such as biochemical functional groups with O donor atoms. The best fitting model was obtained using LC50 metameters based on total metal concentration, indicating that the identification of the bioactive species of metals can be ambiguous, and does not necessarily aid in the prediction of relative metal toxicity with ion characteristics. The modelling of relative metal toxicity using ion characteristics was successful for 24 hr exposure durations using this more complex organism.