Mixture toxicity of copper and zinc to barley at low level effects can be described by the Biotic Ligand Model

Background and aims: The biotic ligand model (BLM) is a bioavailability model for metals based on the concept that toxicity depends on the concentration of metal bound to a biological binding site; the biotic ligand. Here, we evaluated the BLM to interpret and explain mixture toxicity of metals (Cu and Zn). Methods: The mixture toxicity of Cu and Zn to barley (Hordeum vulgare L.) was tested with a 4 days root elongation test in resin buffered nutrient solutions. Toxicity of one toxicant was tested in presence or absence of a low effect level of the other toxicant or in a ray design with constant toxicant ratios. All treatments ran at three different Ca concentrations (0.3, 2.2 and 10mM) to reveal ion interaction effects. Results: The 50 % effect level (EC50) of one metal, expressed as the free ion in solution, significantly (p