Lead isotope ratio analysis by inductively coupled plasma sector field mass spectrometry (ICP-SMS) in soil digests of a depth profile

The application of inductively coupled plasma sector field mass spectrometr y (ICP-SMS) (Finnigan-MAT, Element) to lead isotope ratio determination in soil samples is described. Discrimination of anthropogenic and geogenic lea d sources requires both precise and accurate isotope ratio determination an d also high versatility due to the complex matrix, which is typical for soi l extracts. Moreover, a high sample throughput is required. ICP-SMS could t herefore be implemented as the method of choice. Precision of isotope ratio s of Pb-206/Pb-207 of better than 0.03% was obtained throughout the investi gations in a concentration range of 5-50 ng g(-1) in solution. Accuracy was illustrated by using the NIST SRM 981 isotopic ratio reference standard an d was 0.03% for both the Pb-207/Pb-206 and Pb-208/Pb-207 ratios. In order t o differentiate between anthropogenic and geogenic sources of lead in soils , both lead concentration and isotopic composition were determined by ICP-S MS along a soil profile collected from a Dystric Cambisol in Eastern Austri a. Along the soil profile, a significant change of lead isotopic compositio n could be detected, showing the difference between anthropogenic (surface) and geogenic (parent rock) sources. Along with the total concentration of lead and other soil properties, the contribution of anthropogenic sources t o the lead concentration of soils and their participation in lead mobilizat ion can be estimated.