SEQUENTIAL EXTRACTION OF SOILS FOR MULTIELEMENT ANALYSIS BY ICP-AES

Realistic environmental interpretation of soil contamination depends o n an understanding of how metals are bound to the various phases in th e 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). Eac h of the chemical fractions is operationally defined as follows: (1) e xchangeable; (2) bound to carbonates or specifically adsorbed; (3) bou nd to Fe-Mn-oxides; (4) bound to organic matter and sulphides; and (5) residual. The number of elements determined by ICP-AES has been exten ded to fifteen (Be, Ca, Co, Cr, Cu, Fe, K, Li, Mn, Ni, P, Pb, Ti, V, Z n), which include most of the major elements, thereby increasing the p otential of the sequential extraction method by enabling broader studi es of geochemical associations in soils. The precision was estimated t o be similar to 5% (2 sigma) for each extraction step. The overall rec overy rates of international reference materials were between 85 and 1 10% for most elements, with an average of 92%. There is good agreement between the results for the international reference material (USGS MA G-1) in each extraction step and published values. A wide range of soi l reference materials, including SO-1-SO-4 and BCR141-BCR143, were als o analysed for future comparison. The application of the method to soi ls contaminated by past mining and smelting activities showed distinct ive partitioning patterns of heavy metals from the two sources. The mu ltielement measurements gave useful information to assist in the inter pretation of the possible geochemical forms and sources of the trace e lements in soils.