Modelling toxicity of metal mixtures: A generalisation of new advanced methods, considering potential application to terrestrial ecosystems

ABSTRACT

No chemical properties have been found to be a reliable predictor of metal toxicity, attributed to the influence of various specific processes on metal toxicokinetics and toxicodynamics.Metal toxicity is affected by interactions between metal ions and of metals with organisms. The present review aims to provide an outlook on recent progress in estimating toxicity of metal mixtures. Three methods applied recently have the potential of accounting for the interactions between metals as well as the interactions of metals with organisms. The methods are based on the Biotic Ligand Model (BLM), electrostatic interactions, and Windermere Humic Aqueous Model (WHAM). These methods can be generalised to a common principle that affinity of metals for binding sites on sorption surfaces (i.e., biotic ligands on organisms, plasma membrane surface, and humic acid-surrogated biological surface) is a unifying factor for the biological response. The scientific basis for these approaches was reviewed in the present study, accompanied by a preliminary assessment on the toxicity of Cu²⁺, Ag⁺, Zn²⁺, and their binary mixtures to lettuce, Lactuca sativa, using previously published data. The difference in the predictive performance of the modelling approaches reflects the difference in the simulation of metal-ligand binding and is related to the specific exposure conditions considered.

KEYWORDS:

• Biotic ligand
• electrostatic
• metal mixture
• plant
• toxicity
• WHAM

Acknowledgments

The authors would like to thank Dr. Thomas Kinraide (U.S. Department of Agriculture, retired) for helping them to improve the figure simulating theories of the electrostatic model.