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

The objective of this study was to employ radiochemical methods to assess the importance and extent of the readsorption and redistribution of lead in the standards, measurement and testing programmeʹs (SM&T) sequential extraction 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 readsorbed, while negligible readsorption was detected for the oxidisable fraction. Statistically significant correlations were observed between readsorption from the first two fractions and both the total iron content and the organic carbon matter even at low organic contents (i.e. less than 6wt.%). By following the radiotracer activity through the first two steps of the method, the reducible fraction was shown to play an important role in scavenging lead released from the exchangeable soil fraction. The radiotracer partitioning results were employed to "correct" for the redistribution effects yielding the "true" fractionation of the Pb in the samples.