SREL Reprint #2304

Use of ion characteristics to predict relative toxicity of mono-, di- and trivalent metal ions: Caenorhabditis elegans LC50

 Christopher P. Tatara1,2, Michael C. Newman3, John T. McCloskey1, and Phillip L. Williams4

1University of Georgia, Savannah River Ecology Laboratory, P.O. Drawer E, Aiken, SC 29802, USA
2Institute of Ecology, University of Georgia, Athens, GA 30602-2202, USA
3College of William and Mary, Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062, USA
4Environmental health Science Program, University of Georgia, Athens, GA 30602, USA

Abstract: Predictive models for relative toxicity of divalent metal ions using ion characteristics have been produced with both Microtox®, a 15 min microbial bioassay, and the 24 h Caenorhabditis elegans bioassay. Relative toxicity of mono-, di- and trivatent metal ions has also been successfully modeled using ion characteristics with the Microtox® bioassay. This study extends this approach to include longer exposure durations (24 h) and a more complex organism (metazoan). Twenty-four-hour LC50s (expressed as total and free ion concentrations) for the free-living 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 medium. Relative metal toxicity was predicted with least squares linear regression and several ion characteristics. Toxicity was most effectively predicted (r2 = 0.85) with a two-variable model containing |log KOH| (where KOH is the first hydrolysis constant) and X2mr (the 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 X2mr reflects binding to soft ligands such as those with S donor atoms. The use of LC50s based on free ion concentrations did not significantly improve model fit.  The results of this study are consistent with earlier models generated with Microtox® 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 the relative toxicity of metal ions that vary widely in both valence and binding tendency.

Keywords: Caenorhabditis elegans; Metal; Nematode; Prediction; Toxicity

SREL Reprint # 2304

Tatara, C.P., M.C. Newman, J.T. McCloskey, and P.L. Williams. 1998. Use of ion characteristics to predict relative toxicity of mono-, di- and trivalent metal ions: Caenorhabditis elegans LC50. Aquatic Toxicology 42:255-269.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).