Determination of heavy metals in lake and river sediments by selective leaching

The sequential extraction procedure developed by Ure et al.(1) as a reference method for speciation of heavy metals in sediments has been extended. The three fractions as 1. exchangeable and bound to carbonate, 2. reducible, bound to Fe/Mn oxides, 3. oxidizable, bound to organic and sulfide compounds, were further completed by a strong acid-soluble fraction, the "pseudototal fraction." The extracting solutions were cone. nitric acid and perchloric acid. This fraction has the advantage of giving a better insight into the association mechanism of metals with mineralogical phases of the sediments. Zinc, Ni, Cd, Cr, Cu, and Pb were determined in the extracts. The sum of the contents obtained with the four-step selective leaching method was compared with those obtained with the total acid-soluble procedure and a good agreement was found. Most of the elements were found in the acid-soluble fractions indicating stable species of sediments. The critically examined three-step sequential extraction method should be used to compare the data produced by different laboratories, but the strong acid-soluble fraction of elements could add more valuable information.