Sequential chemical extraction

Gibson, M.J. and Farmer, J.G., Multi-step sequential chemical extraction of heavy metals from urban soils, Environ. Poll. (Ser. B), 11, 117, 1986. 

Ma L.Q., Rao G.N. Effects of phosphate rock on sequential chemical extraction of lead in contaminated soils. J Environ Qual 1997b 26 788-794. 

The next step is to select a protocol for isolating cell walls that suits the type of material to be investigated and the reasons for doing the research (see Critical Parameters). Two basic protocols are described, one for plant tissue that does not contain starch (see Basic Protocol 2) and one for plant tissue that does contain starch (see Basic Protocol 3), as well as three alternate protocols that can be used and modified to suit (see Commentary). The final step is fractionation of cell wall polysaccharides, which is a sequential chemical extraction of polysaccharides from the walls (see Basic Protocol 4). Table E3.1.1 provides a more detailed description of the protocols presented in this unit. 

Speciation science seeks to characterise the various forms in which PTMs occur or, at least, the main metal pools present in soil. This chapter provides a review of the single and sequential chemical extraction procedures that have been more widely applied to determine the plant and the human bioavailability of PTMs from contaminated soil and their presumed geochemical forms. Examples of complementary use of chemical and instrumental techniques and applications of PTMs speciation for risk and remediation assessment are illustrated. 

This chapter provides a review of the single and sequential chemical extraction procedures that have been more widely applied to estimate the plant and the human bioavailability of PTMs from contaminated soil and their presumed geochemical forms. 

Ryan, P. C., Wall, A. J., Hillier, S., and Clark, L. (2002). Insights into sequential chemical extraction procedures from quantitative XRD A study of trace metal partitioning in sediments related to frog malformities. Chem. Geol. 184, 337-357. 

Kennedy, V. H., Sanchez, A. L., Oughton, D. H., and Rowland, A. P. (1997). Use of single and sequential chemical extractants to assess radionuclide and heavy metal availability from soils for root uptake. Analyst 122, 89R-100R. 

Despite of clear advantages of a differentiated analysis over investigations of total sample - sequential chemical extraction is probably the most useful tool for predicting long-term adverse effects from con-tamined solid material - it has become obvious that there are many problems associated with these procedures (e.g., Kersten Fdrstner, 1986 Rapin et al. 1986) ... 

Kim CS, Bloom NS, Rytuba JJ, Brown GE Jr (2002a) Mercury speciation by extended X-ray absorption fine structure (EXAFS) spectroscopy and sequential chemical extractions An intercomparison of speciation methods. Environ Sci Technol (submitted)... 

Geochemical analyses of the contaminated sediments in the root zone using sequential chemical extractions showed that greater than half of the arsenic is strongly adsorbed (Keon et al. 2000, 2001). A mixture of arsenic oxidation states and associations was observed and supported by bulk XANES and EXAFS data collected at the SSRL. Arsenic in the upper 40 cm of the wetland, which contains the peak corresponding to maximum deposition, appears to be controlled by iron phases, with a small contribution from sulfidic phases. The results suggest that iron oxide phases may be present in the otherwise reducing wetland sediments as a substrate onto which arsenic can adsorb, perhaps due to cattail root plaque formation. 

Metal-complexation/SFE using carbon dioxide has been successfully demonstrated for removal of lanthanides, actinides and various other fission products from solids and liquids (8-18), Direct dissolution of recalcitrant uranium oxides using nitric acid and metal-complexing agents in supercritical fluid carbon dioxide has also been reported (79-25). In this paper we explored supercritical fluid extraction of sorbed plutonium and americium from soil using common organophosphorus and beta-diketone complexants. We also qualitatively characterize actinide sorption to various soil fractions via use of sequential chemical extraction techniques. 

Post-SFE soils and the liquid extract were radiologically characterized using both gamma-ray spectroscopy and alpha spectrometry techniques. Sequential chemical extractions were performed on both pre-SFE and post-SFE soils to obtain information related to the percent plutonium and americium removed from the various soil fractions. Sequential chemical extraction analysis was performed on 1 g batches of soils. Sequential chemical extraction techniques were the same as those employed by Litaor and Ibrahim (26) and Tessier et al (27). Both techniques were employed for comparative purposes on pre-SFE samples, but only the technique of Litaor et al was used to characterize plutonium and americium in the post-SFE samples. 

Sequential chemical extraction techniques are widely published in the literature and useful for determining the geochemical fractionation of metals in soils and sediments (27-29). Even though some methods may suffer from limitations (e.g., re-adsorption) the data are useful for assessing die conditions under which bound metal can be released from the soil. 

Figure 4, Sequential chemical extraction results for plutonium on pre-SFE...

Sequential chemical extractions on pre-SFE soils, using two different procedures for comparison, were conducted. The results for plutonium are found in Figure 4. The data indicate there is variability in the results between different procedures. The procedure of Litaor and Ibrahim was viewed as the most conservative because it tended to extract plutonium from all phases leaving approximately 12.8% 1 assigned to the residual. The sequential chemical extraction results for americium on pre-SFE soil are found in Figure 5. Results indicate americium is primarily associated with the reducible soil fraction. Comparison of the data from the two different sequential chemical extraction techniques shows similar results. 

Experimental results from sequential chemical extractions performed on post-Sra soils (Figure 6) using the TBP - HFA system show that most (86% 2) of the remaining plutonium not removed by SFE is associated with the reducible (sesquioxide) mineral fraction of the soil. Approximately 10% of the remaining plutonium is partitioned into the residual fraction and the balance ( 4%) is found in the oxidizable and carbonate bound fractions. 

Table 1.1. Sequential chemical extraction steps for isolation of phytate (de Groot and Golterman, 1993). (NTA, nitriloacetic acid EDTA, ethylenediaminetetraacetic acid.) ...

Sequential chemical extraction involves treatment of a sample of soil or sediment with a series of reagents in order to partition the trace element content. The principal advantage claimed for sequential extraction over the use of single extractants is that the phase specificity is improved. This technique has been used to determine the chemical forms of trace elements in soils, sediments, and suspended solids in natural waters, and is based theoretically and experimentally on more than 100 years of research (Jackson, 1985). A basic requirement of any extraction procedure should be the ability of the extractant to dissolve a specific component of a soil or sediment (Chao, 1984). Many different methods have been employed to fractionate trace elements, and these have proved useful for metal speciafion (Jones and Hao, 1993). Reviews of the fractionation methods used to determine the chemical forms of trace elements in soils and sediments (e.g. Pickering, 1981, 1986 Ross, 1994 Sheppard and Stevenson, 1997), in geochemical exploration (Chao, 1984), and in natural waters (Florence and Batley, 1977) are available. A few commonly used fractionation schemes for delineating different forms of trace elements are given in Table 6. 

Morrison et al. (1989) stated research has so far failed to provide a realistic estimate of the toxic or available fraction in soils by chemical tests. Elaborate sequential chemical extraction schemes, designed to release a particular geochemical fraction, have frequently been used. However, little progress has been made in identifying the particular species of the element that may contribute to its bioavailability. 

Characterization of sediment components can be achieved directly using sequential chemical extractions. The advantages and limitations of this approach are discussed in the section, Partial chemical extractions and sediment sourcing. In this section, numerical approaches to determining the sediment components are addressed. 

Table 2 Sequential chemical extraction for isolation of various phosphate fractions involving use of chelating agents at near-neutral pH ...

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