Surface Complexation Modeling THE USE OF ASSEMBLAGE MODELS TO DESCRIBE TRACE ELEMENT PARTITIONING, SPECIATION, AND FATE: A REVIEW

The fate of trace elements in soils, sediments, and surface waters is largely determined by their binding to reactive components, of which organic matter, metal oxides, and clays are considered most important. Assemblage models, combining separate mechanistic complexation models for each of the reactive components, can be used to predict the solid-solution partitioning and speciation of trace elements in natural environments. In the present review, the authors provide a short overview of advanced ion-binding models for organic matter and oxides and of their application to artificial and natural assemblages. Modeling of artificial assemblages of mineral components and organic matter indicates that the interactions between organic and mineral components are important for trace element binding, particularlyforoxyanions.Themodelingofsolid-solutionpartitioninginnaturalsystemsisgenerallyadequateformetalcationsbutlessso for oxyanions, probably because of the neglect of organic matter-oxide interactions in most assemblage models. The characterization of natural assemblages in terms of their components (active organic matter, reactive oxide surface) is key to successful model applications. Improved methods for characterization of reactive components in situ will enhance the applicability of assemblage models. Collection of compositional data forsoilandwater archetypes,or thedevelopmentof relationships toestimate compositions fromgeospatially available data, will further facilitate assemblage model use for predictive purposes. Environ Toxicol Chem 2014;33:2181-2196. # 2014 SETAC