Kd distributions in freshwater systems as a function of material type, mass-volume ratio, dissolved organic carbon and pH

The contamination of freshwater systems by metals is a worldwide problem due to their toxicity, abundance and persistence in the environment. One of the main processes affecting their residence time in freshwater systems is their solid-liquid fractionation, often modeled by the Kd approach defined as the concentration ratio between the particulate and dissolved phases under the assumptions of reversibility, equilibrium and trace conditions. Because Kd is an empirical parameter that depends on several environmental factors, its variability can cover orders of magnitude for a single element. Such variability is unknown for most case studies, but the modelers need it to evaluate the uncertainty of their calculations. In order to fill this gap, this paper presents statistical Kd distributions for in situ suspended matters as a function of suspended load, dissolved organic carbon and pH. They were obtained using a database containing 8564 Kd values from 50 elements, classified as a function of three exchange conditions (adsorption, desorption and in situ) and two environmental components (suspended and deposited sediments). These distributions and relations can be used to reduce of several order of magnitudes the global variability of Kd values in the case where in situ data are not available.