Comparison of two extraction procedures for determination of trace metals in soil by atomic absorption spectrometry

The study compares nitric acid and ethylenediaminetetraacetic acid (EDTA) extraction of forest soils for the analysis of trace metals Fe, Mn, Zn, Cu, Pb, and Cd. Fifty forest soil samples from ten different locations were extracted using both methods. The two extraction procedures were compared through regression analysis for each element. All elements were analysed by flame atomic absorption spectrometry method (AAS). The results show that both extracting procedures are only partially effective for most of the measured trace elements in soil. The extraction with diluted HNO3 was incomplete, as large amounts of siliceous material remained undigested. Recoveries obtained by this method for Fe, Mn, Zn, Cu, Pb, and Cd on certified reference material (San Joaquin Soil) were 34, 79, 47, 56, 71, and 102%, respectively. EDTA extraction was even less effective and is considered to reflect the quantity of bioavailable metals. The respective recoveries were 2, 45, 7, 20, 38 and 74%. The regression analyses performed for EDTA-extractable vs. HNO3-extractable metals of forest soils showed high and significant correlation for all examined metals, except Fe.