Naturally elevated metal contents of soils in northeastern North Dakota, USA, with a focus on cadmium

Abstract

Association of element concentrations for the escarpment soils of northeastern North Dakota formed from different geologic parent materials was determined based on geochemical data. These soils overlie the Cretaceous Pierre Formation, and parent materials consist of shale rich glacial till, residual shale, and colluvial materials. Samples were analyzed for cadmium and other trace elements using nitric acid digestion followed by optical emission spectroscopy. Morphologic and laboratory analysis of soil cores indicate high clay content, indicative of the influence of shale residuum on the parent materials of the escarpment soils. An average, cadmium concentration of 0.24±0.22 mg/kg was determined for 136 samples from eight (approx. 2.4 m deep) cores. The concentration of molybdenum had a range between 0.00 and 7.99 mg/kg. Zinc levels determined in the samples had a wide range between 18.76 and 128.02 mg/kg. Principal component analysis revealed that elevated trace element concentrations for the shale-rich portion of the soils in northeastern North Dakota are linked to a variety of factors including organic matter content, pH, elevation, and electrical conductivity. Results of this study suggest that erosion and transport of Cretaceous shales downslope on the escarpment have resulted in enriched trace element concentrations in the soils.