Urban soils can be exposed to many potential sources of trace elements. This can be problematic if, for example, one wanted to establish a community garden but the soil at the site is not safe for growing plants for human consumption due to the contamination. | Photo courtesy of Pacific Regional Soil Science Society. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives International License. Depending on the study objectives, it may be of interest to differentiate between the different forms (species) of an element present in a soil. Sometimes this is done using a sequential extraction, which extracts the same sample with a series of solutions, of increasing strength. Sequential extractions can be problematic in that the fractions may not actually remove specific chemical forms that are identifiable. Further, the sum of the fractions may not match with the total metals analysis. Using a combination of single extractants can be an alternative. Speciations will be specific to an element. As with any analysis, it is important to consider the source of your samples, sample characteristics, and the purpose of the analysis. Resources and References Bertsch, P.M. and P.R. Bloom. 1996. Aluminum. In Sparks, D.L. (ed). Methods of Soil Analysis: chemical methods. Part 3. Soil Sci. Soc. Am. Book Series No. 5. ASA-SSSA, Madison, WI. Gleyzes, C., S. Tellier, and M. Astruc. 2002. Fractionation studies of trace elements in contaminated soils and sediments: a review of sequential extraction procedures. Trends in Analytical Chemistry 21:451-467. Hendershot, W.H., H. Lalande, D. Reyes, and J.S. MacDonald. 2008. Trace element assessment. In Carter, M.R., and E.G. Gregorich (eds). Soil Sampling and Methods of Analysis. 2nd ed. Canadian Society of Soil Science, CRC Press and Taylor & Francis Group. Oxford, UK. Kabata-Pendias, A. 2004. Soil–plant transfer of trace elements – an environmental issue. Geoderma 122:143-149.