Modeling toxicity of binary metal mixtures (Cu2+–Ag+, Cu2+–Zn2+) to lettuce, Lactuca sativa, with the biotic ligand model

Authors

  • T.T. Yen Le,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, Nijmegen, The Netherlands
    2. National Institute for Public Health and the Environment, Laboratory for Ecological Risk Assessment, Bilthoven, The Netherlands
    Search for more papers by this author
  • Martina G. Vijver,

    1. Leiden University, Institute of Environmental Sciences, Department of Conservation Biology, Leiden, The Netherlands
    Search for more papers by this author
  • A. Jan Hendriks,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, Nijmegen, The Netherlands
    Search for more papers by this author
  • Willie J.G.M. Peijnenburg

    1. National Institute for Public Health and the Environment, Laboratory for Ecological Risk Assessment, Bilthoven, The Netherlands
    2. Leiden University, Institute of Environmental Sciences, Department of Conservation Biology, Leiden, The Netherlands
    Search for more papers by this author

Abstract

The biotic ligand model (BLM) was applied to predict metal toxicity to lettuce, Lactuca sativa. Cu2+ had the lowest median effective activity (EA50M), compared with Ag+ and Zn2+ (EA50Cu = 2.60 × 10−8 M, EA50Ag = 1.34 × 10−7 M, EA50Zn = 1.06 × 10−4 M). At the 50% response level, the fraction of the total number of biotic ligands occupied by ions (f50M) was lowest for Ag+ among the metals (f50Ag = 0.22, f50Cu = 0.36, f50Zn = 0.42). Cu2+ had the highest affinity for biotic ligands compared with Ag+ and Zn2+, as shown by stability constants of the cation–biotic ligand binding, expressed as log KMBL (log KCuBL = 7.40, log KAgBL = 6.39, log KZnBL = 4.00). Furthermore, the BLM was combined with the toxic equivalency factor approach in predicting toxicity of mixtures of Cu2+–Zn2+ and Cu2+–Ag+. The fraction of biotic ligands occupied by ions was used to determine the relative toxic potency of metals and the toxic equivalency quotient (TEQ) of mixtures. This approach allowed for including interactions in estimating mixture toxicity and showed good predictive power (r2 = 0.64–0.84). The TEQ at the 50% response level (TEQ50, Cu2+ equivalents) for Cu2+–Zn2+ mixtures was significantly lower than the value for Cu2+–Ag+ mixtures. Joint toxicity depended on both TEQ and specific composition of the mixture. The present study supports the use of the accumulation of metal ions at the biotic ligands as a predictor of toxicity of single metals and mixtures. Environ. Toxicol. Chem. 2013;32:137–143. © 2012 SETAC

Ancillary