Radiochemical assessment of the readsorption and redistribution of lead inthe SM&T sequential extraction procedure

The objective of this study was to employ radiochemical methods to assess t he importance and extent of the readsorption and redistribution of lead in the standards, measurement and testing programme's (SM&T) sequential extrac tion procedure. Step-wise tests indicated that 60% to over 90% of the lead extracted from the exchangeable fraction was readsorbed. Approximately 35% to over 85% of the lead extracted from the reducible fraction was readsorbe d, while negligible readsorption was detected for the oxidisable fraction. Statistically significant correlations were observed between readsorption f rom the first two fractions and both the total iron content and the organic carbon matter even at low organic contents (i.e. less than 6 wt.%). By fol lowing the radiotracer activity through the first two steps of the method, the reducible fraction was shown to play an important role in scavenging le ad released from the exchangeable soil fraction. The radiotracer partitioni ng results were employed to "correct" for the redistribution effects yieldi ng the "true" fractionation of the Pb in the samples. (C) 2001 Elsevier Sci ence B.V. All rights reserved.