A modified method of total elemental analysis for determining background metals in Tennessee

In order to assess the impact of metal pollution, a knowledge of indigenous metal levels is required. Data for background metal concentrations for soils and parent materials in Tennessee are not available in scientific literature.

The objective of this study was to establish background metal concentrations on the major physiographic regions or Major Land Resource Areas (MLRAs) of Tennessee. Background metal concentration information will serve as a future reference for interpreting metal data. To meet this objective, it was necessary to test and evaluate an acid digestion procedure using a microwave oven for preparing soil samples for total analysis.

An acid digestion procedure for total elemental analysis was evaluated on soils of different textures to establish background metal concentrations. Samples were dissolved in 5 ml of aqua-regia and 2 ml of hydrofluoric acid (HCI-HNO₃-HF). Samples were heated in a microwave oven to facilitate reactions. Boric acid (1 gm) was then added to neutralize the hydrofluoric acid. The solutions were transferred to 100 ml volumetrics and brought to volume for analysis. The elements: Al, Ca, Fe, K, Mg, Na, P, S, Si, and Ti, were analyzed by inductively coupled argon plasma atomic emission spectrometer (ICAPAES). Recovery rates were established by analysis of a coal fly ash standard (National Bureau of Standards). Recovery rates ranged from 88.9 percent for Fe to 101 percent for Si and Na. The procedure was tested over a broad range of textures using deep core samples. These samples were of loess, alluvium, and Tertiary Sand parent materials from the University of Tennessee Ames Plantation in Southwest Tennessee. A modification for sandy textured samples involved overnight digestion in hydrofluoric acid to achieve total dissolution.

This digestion procedure was applied to samples from thirteen selected pedons from six of the eight MLRAs in Tennessee. Total analysis for twenty-three elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Si, Sr, Ti, Zn, Zr) were then completed on these samples using ICAPAES. Generally, metal concentrations, in all regions of the state, were within the established ranges for average elemental concentrations in soils and crustal rocks.