SREL Reprint #2116

 

 

 

Predicting the relative toxicity of metal ions using ion characteristics:
Microtox bioluminescence assay


McCloskey, J.T., M.C. Newman and S.B. Clark. 1996


ABSTRACT:
Quantitative structure-activity relationships (QSAR's) have been used to predict the relative toxicity of organic compounds. Although not as common, ion characteristics have also proven useful for predicting the relative toxicity of metal ions. The purpose of this study was to determine if the relative toxicity of metal ions using the Microtox® bioassay was predictable using ion characteristics. Median effect concentrations (EC50's) were determined for 20 metals in a NaNO3 medium, which reflected freshwater speciation conditions, using the Microtox® bacterial assay. The log of EC50 values were modeled using several ion characteristics and Akaike’s Information Criterion (AIC) was calculated to determine which ion characteristics provided the best fit. Whether modeling total ion (unspeciated) or free ion (speciated) EC50 values, the one variable which best modeled EC50's was the softness index (sp) ([coordinate bond energy of the metal fluoride - coordinate bond energy of the metal iodide]/coordinate bond energy of the metal fluoride), while a combination of cm2r (cm = electronegativity, r = Pauling ionic radius) and |log KOH | (absolute value of the log of the first hydrolysis constant (KOH for Mn+ + H2O ® MOHn-1 + H+)) was the best two variable model. Other variables including DE0, cm2r (one variable models) and (AN/DIP, DE0), (cm2r, Z2/r) (two variable models) also gave adequate fits. Modeling with speciated (free ion) versus unspeciated (total ion) EC50 values did not improve fits. Modeling mono-, di- and trivalent metal ions separately improved the models. We conclude that ion characteristics can be used to predict the relative toxicity of metal ions whether in freshwater (NaNO3 medium) or saltwater (NaCl medium) speciation conditions, and that this approach can be applied to metal ions varying widely in both valence and binding tendencies.

SREL Reprint #2116

McCloskey, J.T., M.C. Newman, and S.B. Clark. 1996. Predicting the relative toxicity of metal ions using ion characteristics: Microtox bioluminesence assay. Environmental Toxicology and Chemistry 15:1730-1737.

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