Solid-solution partitioning of metals in contaminated soils:: Dependence on pH, total metal burden, and organic matter

Environmental risk assessment of metals depends to a great extent on modeling the fate and the mobility of metals based on soil-liquid partitioning coefficients. A large variability is observed among the reported values that could be used to predict metal mobility and bioavailability. To evaluate this, soil-liquid partitioning coefficients (K-d) for many elements but especially for the meta Is cadmium, copper, lead, nickel, and zinc were compiled from over 70 studies of various origins collected from the literature. The relationships between the reported values are explored relative to variations in soil solution pH, soil organic matter (SOM), and concentrations of total soil metal. The results of multiple linear regressions show that K-d values are best predicted using empirical linear regressions with pH (with R-2 values of 0.29-0.58) or with pH and either the log of SOM or the log of total metal and with resulting R-2 values of 0.42-0.76. A semi-mechanistic model based on the competitive adsorption of metal and H+ [dependent on solution pH, total metal content, and log(SOM)] was a better tool to predict dissolved metal concentrations (with R-2 values of 0.61-0.88), with the exception of Pb (at 0.35).