Operational Method to Easily Determine the Available Fraction of a Contaminant in Soil and the Associated Soil-Solution Distribution Coefficient

Abstract

Well understanding the solid/solution partitioning of a contaminant is of first importance to determine its residence time in the environment, environmental availability, or bioavailability. Currently, parameters of contaminant transfer models are derived from two conceptually different approaches: one considering that the totality of the contaminant is in equilibrium between the solid and the solution and the other one considering that only a part of the contaminant can be transferred from the solid to the solution without considering equilibrium. Our work offers to reconcile these two approaches by assuming that the contaminant associated with the solid is present under two fractions: one available at equilibrium with the solution and a second one not available and nontransferable to the solution. We propose to use simple operational batch methods (successive desorption batch experiments or batch desorption conducted at different volumes of solution/mass of solid (V/M) ratios) to check this assumption and to determine the real available contaminant fraction (i.e., the contaminant in the solid which can be at equilibrium with the solution) and its associated solid/solution distribution coefficient. The robustness of the proposed method was tested on simulated conditions, on experiments performed to validate the approach, and on the reinterpretation of literature data. Finally, the use of the available contaminant fraction and its associated solid/solution distribution coefficient in transfer models can improve the predictive modeling of contaminant transfer in the soil/solution/plant system.