When we used the DTPA method to extract heavy metals (Zn, Pb, Cd and Cu) from soils, which fractions exactly extracted by the DTPA (water soluble, exchangeable, organic-bound, carbonate-bound...etc.). I am sure that the DTPA will extract the soluble and exchangeable fractions, but I have not any information about the other fractions. I want any references about these information. I think the DTPA will extract some of the other fractions but which one and how? I want to know that exactly. I don't need information about fractionation methods, they are available everywhere, I want to know exactly which metal fractions could be extracted by the DTPA method.
I think the following might answer your question. www.agriculturejournals.cz/publicFiles/53925.pdf
Read this article as well. international Research Journal of Environment
Sciences ISSN 2319–1414 Vol. 2(4), 59-64, April (2013). It might be of importance.
The DTPA representing plant available forms but for Pb, DTPA isn't a good extractant. For Pb is better CaCl2 0.01 M (acidified with HCl) (Houba et al. 2000) http://www.tandfonline.com/doi/abs/10.1080/00103620009370514
DTPA is a chelatin agent that forms complex with metas, it is the way to extract Fe, Zn, Cd, Ni, Cr, Cu. it a ususal method in agriculture for minoritary elemts in soil.
It could be useful to chech the following link (USD and EPA web pages)
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1244466.pdf
http://agsci.psu.edu/aasl/soil-testing/soil-methods
In these page you can find recommendation about differente SEP (sequential extraction procedures)
DTPA-extractable fractions of heavy metals were extracted from 10 g weighing samples of soil with 20 ml of extracting solution (0.005M DTPA, 0.01M CaCl2 and 0.1M TEA adjusted to pH 7.3) according to Lindsay and Norvell (1978) procedure.
Lindsay W.L., Norvell W.A. (1978): Development of a DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Amer. J., 42: 421–428.
Mamdouh, the DTPA is able to extract a portion of each of the pools that you suggested, and especially from the Fe and Al sesquioxides as the chelating agent is able to complex and solubilize those minerals in addition to the heavy metals directly. Since much of the heavy metals are typically bound to the Al and Fe minerals, the heavy metals bound to them will be relinquished into solution from the chelating agent. How much of each pool is plant available? that is another question.
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