Examination of cadmium sorption characteristics for a boreal soil near Fairbanks, Alaska

The objective of this research was to better understand cadmium (Cd)mobility in an organic-rich, boreal soil. Cadmium was selected for the study because of its tendency to be more mobile in soils than other heavy metals, such as lead or mercury. The release of metals from soil is a concern for northern regions where soils are gradually warming, resulting in an increased rate of natural organic matter (NOM)decomposition and soil erosion. Soil samples were collected from three principle soil horizons at a research site in the Caribou-Poker Creeks Research Watershed (CPCRW), near Fairbanks, Alaska. A dilute Cd solution was added to the soil and the soil solution was allowed to mix for 72 h. The soil solution was then passed through a 75 m sieve and a 0.3 m filter. Particulate samples retained on the sieve and filter were analyzed by atomic absorption (AA)to determine how much Cd was bound to the different size particles. The NOM in each particle size fraction was analyzed by pyrolysis-gas chromatography/mass spectrometry (py-GC/MS)to determine the nature of the NOM present. Our results showed that the concentration of Cd was almost equal for the different particle sizes in each horizon. That is, the amount of Cd associated with particles larger than 75 m was nearly the same, on a per mass basis, as the amount of Cd associated with particles ranging in size between 0.3 and 75 m. Since the mass ratio of Cd to solids normally increases as particle size decreases, this result suggested unusual sorption behavior. Based on the Cd distribution among the particles and the percentage of NOM in each particle size range, it is believed that NOM is a primary factor influencing the sorption behavior of Cd in the boreal soil tested.