PREDICTING RELATIVE METAL TOXICITY WITH ION CHARACTERISTICS - CAENORHABDITIS-ELEGANS LC50

Quantitative Structure Activity Relationships (QSAR) predict relative toxicity of a family of chemicals from fundamental and surrogate molec ular qualities. Most QSARs are developed for organic toxicants, with i norganic toxicants (metals) being under-represented. Successful predic tive models for relative toxicity of divalent metal ions using ion cha racteristics have been produced using Microtox(R), a 15 min microbial bioassay. The present study extends this approach to longer exposure d urations (24 h), and a more complex organism (metazoan). Twenty-four h our 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 pred icted with least squares linear regression and several ion characteris tics. Toxicity was most effectively predicted (r(2) = 0.89) with \ log k(OH) \ (where K-OH is the first hydrolysis constant), which reflects a metal ion's tendency to bind to intermediate ligands such as bioche mical functional groups with O donor atoms. The best fitting model was obtained using LC50 metameters based on total metal concentration, in dicating that the identification of the bioactive species of metals ca n be ambiguous, and does not necessarily aid in the prediction of rela tive metal toxicity with ion characteristics. The modelling of relativ e metal toxicity using ion characteristics was successful for 24 h exp osure durations using this more complex organism. Published by Elsevie r Science B.V.