ICP-MS-based tracing of metal sources and mobility in a soil depth profile via the isotopic variation of Sr and Pb

• Published in: International journal of mass spectrometry Vol. 242; no. 2; pp. 243 - 250
• Main Authors: Prohaska, T., Wenzel, W.W., Stingeder, G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-2005
• Subjects: Inductively coupled plasma mass spectrometry; Isotope ratios; Metals; Soil science; Soil science; Inductively coupled plasma mass spectrometry; Isotope ratios; Metals
• ISSN: 1387-3806; 1873-2798
• DOI: 10.1016/j.ijms.2004.11.028

The isotopic compositions of lead and strontium and the total concentration of 11 elements (Rb, Sr, Ca, Ba, Cu, Zn, Mn, Fe, Pb, Cr, Cd) in NH
4NO
3 extracts (reflecting the mobile, bioavailable fraction) and total digests of soil fractions along a soil depth profile were analyzed using sectorfield ICP-MS. This information allows distinguishing between recent external (atmospheric deposition) and primary geogenic sources. Both isotopic systems indicate a clear difference between the surface composition and the composition of lower geogenic levels within the investigated soil profile. An increase of the
87Sr/
86Sr isotope ratio can be observed in the total digest down to a depth of about 120
cm for Sr, whereas Pb shows a stable isotopic composition starting from a depth of about 60
cm. We found increased isotopic ratios of
87Sr/
86Sr in the mobile fraction of the topsoil compared to the subsoil and to the total digest in the topsoil. This observation and the increased Sr levels in the mobile fraction of the topsoil are an indicator for recent deposition of Sr along with the dust derived from the paving of the forest roads in the study area. The significant change of the
87Sr/
86Sr ratios in the total digest at 120
cm depth can be related to a variation in the lithology of this layer, which was confirmed by a concomitant change of the conventionally applied Ti/Zr ratio. This lithogenic inhomogeneity was not apparent from the fairly homogenous distribution of total Sr in the soil profile. Similarly, we were able to distinguish the accumulation of anthroponic heavy metal sources and their recent mobilization within the topsoil from long-term leaching of geogenic sources in deeper soil layers.