Assessing metal contamination of soils has been a difficult task because the metal concentration in soil is not directly correlated to its potential effects. We review an approach, termed the Terrestrial Biotic Ligand Model (TBLM), in which partitioning of metal from soil to soil solution is modelled and the metal in solution interacts with an organism, the biotic ligand, to cause toxicity. The toxicity is modulated by other cations in the soil solution, principally H+, Ca2+, and Mg2+. New results for the model using Ni as the toxic species and barley root elongation as the biological response are presented.
