Extended biotic ligand model for prediction of mixture toxicity of Cd and Pb using single metal toxicity data

The combined toxic effects of Cd and Pb in the presence of different concentrations of Ca2+ were predicted using the biotic ligand model (BLM), with the parameters derived from the Cd‐only and Pb‐only toxicity data. The BLM‐based toxic unit (TU) approach and the proposed BLM‐based fmix approach were used for prediction. The predicted mixture toxic effects using the BLM‐based fmix approach were closer to the observed mixture effects (root mean square error [RMSE] = 9.7 at 25 mM Ca2+) than that using the BLM‐based TU approach (RMSE = 25.6 at 25 mM Ca2+). This can be attributed to the fact that the BLM‐based TU approach only considers the competition between Ca2+ and Cd or Pb, whereas the BLM‐based fmix approach considers both the competition between Cd and Pb and the competition between Ca2+ and Cd or Pb for biotic ligand sites. In addition, the parameters derived from the Cd‐only and Pb‐only solutions in the presence of the background Ca2+ concentration (0.025 mM) could be used to predict the mixture toxic effects at higher Ca2+ concentrations. The BLM‐based fmix approach proposed in the current study suggests a new way of predicting the Cd–Pb mixture toxicity from the single metal toxicity data by adopting the fmix values. Environ. Toxicol. Chem. 2011; 30:1697–1703. © 2011 SETAC