Trace Elements in Benchmark Soils of Oklahoma

Abstract

Natural background concentrations of trace elements in soils must be determined to establish baseline levels for soil remediation and to avoid the establishment of inaccurate or unrealistic guideline levels. The objectives of this study were to establish the background total trace element concentrations including As, Cd, Cr, Cu, Mn, Mo, Ni, Se, Pb, and Zn in 28 Oklahoma benchmark soils and to determine the relationship between soil properties and natural trace element concentrations. Soil samples were analyzed for total trace elements, pH, organic C, clay content, and oxalate‐extractable Al (Alox) and Fe (Feox). Both multiple regression and path analysis were used to examine the relationship between total trace elements and soil properties. The background concentrations of trace elements were (mg kg−1): As (0.75–33.6), Cd (0.13–0.80), Cr (4.30–69.7), Cu (1.94–32.7), Mn (27.4–2165), Mo (0.18–1.80), Ni (2.41–57.3), Pb (2.60–31.7), Se (below detection limit, i.e., <1.25), and Zn (15.3–142). Path analysis confirmed the relationships of the multiple regression but in some cases allowed us to more specifically identify the soil property most associated with the total trace element. In our study, total soil Cd, Cr, Cu, Ni, Pb, and Zn concentrations were dependent largely on clay content. Organic C content also significantly affected total soil Pb concentrations. Total soil As, Mn, and Mo concentrations were most dependent on Alox levels. Path analysis separated direct effects from indirect effects and proved to be an asset when determining which soil properties controlled total soil trace element concentrations.