Possible application of stable isotope compositions for the identification of metal sources in soil

Metals in soil are potentially harmful to humans and ecosystems. Stable isotope measurement may provide fingerprint information on the sources of metals. In light of the rapid progress in this emerging field, we present a state-of-the-art overview of how useful stable isotopes are in soil metal source identification. Distinct isotope signals in different sources are the key prerequisites for source apportionment. In this context, Zn and Cd isotopes are particularly helpful for the identification of combustion-related industrial sources, since high-temperature evaporation-condensation would largely fractionate the isotopes of both elements. The mass-independent fractionation of Hg isotopes during photochemical reactions allows for the identification of atmospheric sources. However, compared with traditionally used Sr and Pb isotopes for source tracking whose variations are due to the radiogenic processes, the biogeochemical low-temperature fractionation of Cr, Cu, Zn, Cd, Hg and Tl isotopes renders much uncertainty, since large intra-source variations may overlap the distinct signatures of inter-source variations (i.e., blur the source signals). Stable isotope signatures of non-metallic elements can also aid in source identification in an indirect way. In fact, the soils are often contaminated with different elements. In this case, a combination of stable isotope analysis with mineralogical or statistical approaches would provide more accurate results. Furthermore, isotope-based source identification will also be helpful for comprehending the temporal changes of metal accumulation in soil systems.

Automated summary

Stable isotope measurements hold great potential for identifying metal sources in soil, with specific isotopic signals serving as key prerequisites for source allocation. In particular, zinc and cadmium isotopes are valuable for identifying combustion-related industrial sources, while uncertainties may arise from biogeochemical low-temperature fractionation of other elements. Isotope-based source identification, in combination with other analytical approaches, can offer more accurate results for understanding the temporal changes of metal accumulation in soil systems.