Partitioning of Trace Metals in a Macrotidal Estuary. Implications for Contaminant Transport Models

The estuarine geochemical behaviour of trace metals has been studied in a series of experiments using samples from the Dee Estuary (north-east Wales) spiked with radiotracers 109Cd, 51Cr, 137Cs, 59 Fe, 55Mn and 65Zn. The solid-solution phase partitioning, quantified using KDs, is dependent on salinity, particle size/composition (operationally separated in settling experiments), pre-equilibrated speciation of isotopes, and the phase selected to encompass flocculant products. Although quantitatively the results are metal-specific and site-(estuary-) specific, these concepts are generally applicable to predictive estuarine contaminant transport models. To this end, a model for the removal of dissolved Cr in an estuarine turbidity maximum is developed.