SEQUENTIAL EXTRACTION OF SOILS FOR MULTIELEMENT ANALYSIS BY ICP-AES

Realistic environmental interpretation of soil contamination depends on an understanding of how metals are bound to the various phases in the soil. A five-step sequential chemical extraction scheme, originally designed for sediment analysis by flame atomic adsorption spectroscopy (FAAS), has been developed for the multielement analysis of soils by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Each of the chemical fractions is operationally defined as follows: (1) exchangeable; (2) bound to carbonates or specifically adsorbed; (3) bound to Fe-Mn-oxides; (4) bound to organic matter and sulphides; and (5) residual. The number of elements determined by ICP-AES has been extended to fifteen (Be, Ca, Co, Cr, Cu, Fe, K, Li, Mn, Ni, P, Pb, Ti, V, Zn), which include most of the major elements, thereby increasing the potential of the sequential extraction method by enabling broader studies of geochemical associations in soils. The precision was estimated to be similar to 5% (2 sigma) for each extraction step. The overall recovery rates of international reference materials were between 85 and 110% for most elements, with an average of 92%. There is good agreement between the results for the international reference material (USGS MAG-1) in each extraction step and published values. A wide range of soil reference materials, including SO-1-SO-4 and BCR141-BCR143, were also analysed for future comparison. The application of the method to soils contaminated by past mining and smelting activities showed distinctive partitioning patterns of heavy metals from the two sources. The multielement measurements gave useful information to assist in the interpretation of the possible geochemical forms and sources of the trace elements in soils.