USE OF ION CHARACTERISTICS TO PREDICT RELATIVE TOXICITY OF MONOVALENT, DIVALENT AND TRIVALENT METAL-IONS - CAENORHABDITIS-ELEGANS LC50

Predictive models for relative toxicity of divalent metal ions using i on characteristics have been produced with both Microtox(R), a 15 min microbial bioassay, and the 24 h Caenorhabditis elegans bioassay. Rela tive toxicity of mono-, di- and trivalent metal ions has also been suc cessfully modeled using ion characteristics with the Microtox(R) bioas say. This study extends this approach to include longer exposure durat ions (24 h) and a more complex organism (metazoan). Twenty-four-hour L C50s (expressed as total and free ion concentrations) for the free-liv ing soil nematode, C. elegans, were determined for Li: Na, Mg, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Cs, Ba, La, and Pb in an aqueous m edium. Relative metal toxicity was predicted with least squares linear regression and several ion characteristics. Toxicity was most effecti vely predicted (r(2) = 0.85) with a two-variable model containing \log K-OH\ (where K-OH is the first hydrolysis constant) and chi(m)(2)r (t he covalent index). The first hydrolysis constant reflects a metal ion 's tendency to bind to intermediate ligands such as biochemical groups with O donor atoms, while X(m)(2)r reflects binding to soft ligands s uch as those with S donor atoms. The use of LC50s based on free ion co ncentrations did not significantly improve model fit. The results of t his study are consistent with earlier models generated with Microtox(R ) data, with the exception of barium, which was much more toxic to C. elegans than would be predicted from the model. We conclude that, with thoughtful application, ion characteristics can be used to predict th e relative toxicity of metal ions that vary widely in both valence and binding tendency. (C) 1998 Elsevier Science B.V. All rights reserved.