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

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.