A baseline characterization of trace elements in Texas soils

Abstract

A baseline survey of concentrations of Mn, Fe, Zn, Cu, Se, As, Cd, Cr, Co, Pb, Ba, and Ni was performed for 100 soils from seven Land Resource Areas of Texas. Nearly 300 soil samples from the upper, middle, and lower depths of selected pedons were analyzed for trace element concentrations by three extraction methods using inductively coupled plasma-atomic emission spectroscopy. The first method utilized DTPA, which quantities concentrations that are considered ''plant available''. A nitric acid (HNO₃) digestion was used to quantify element concentrations that are acid-extractable while a hydrofluoric acid (HF) digestion gave total element concentrations. Results were compared to the United States Environmental Protection Agency's (USEPA) maximum allowable background concentrations of elements in soils for sewage sludge application. Elements in the study soils were well below USEPA limits. When compared to the median concentration of elements on a worldwide basis, all except Co, As, and Se were found in concentrations lower than the worldwide median but even these elements were well within the published range. Trends in the depth distribution of elements were observed. In general, the surface horizons of the Edwards Plateau/Grand Prairie and Blackland Prairies' soils were higher in trace elements than the middle or lower depths due to the dominance of Mollisols and Vertisols with mollic epipedons. Alfisols and Ultisols of the East Texas Timberlands and Claypan Region lead to trace element concentration in the control section. Concentrations of trace elements were found in the deepest horizons studied for the Central Basin due to the igneous parent materials. No distribution trend was observed for the soils of the Coast Prairie. Soil properties that influence the amount of trace elements in soils as well as their location in the soil profile were investigated by correlation analysis. Sand, clay, and CEC appeared to be the best soil properties correlated to trace element concentrations, while organic C and CaCO₃ equivalent showed fair correlations.