Sequential organic-bound

Thorium is a highly insoluble element, mainly carried in the particulate form in river waters. This is well shown by Th data for the MacKenzie river (Vigier et al. 2001) and for the Kalix river (Andersson et al. 1995 Porcelli et al. 2001) in both cases, more than 95% of Th is carried by >0.45 pm particles. An important part of this Th is included within detrital material. This is illustrated by sequential extractions performed on sediments from the Witham river (Plater et al. 1992), which show the very low amount of Th in ion-exchangeable and organic-bound fractions compared to Th in Fe-Mn oxides... 

Denmark 1.5 days after the explosion. Air samples collected at Roskilde, Denmark on April 27-28, contained a mean air concentration of 241Am of 5.2 pBq/m3 (0.14 fCi/m3). In May 1986, the mean concentration was 11 pBq/m3 (0.30 fCi/m3) (Aarkrog 1988). Whereas debris from nuclear weapons testing is injected into the stratosphere, debris from Chernobyl was injected into the troposphere. As the mean residence time in the troposphere is 20-40 days, it would appear that the fallout would have decreased to very low levels by the end of 1986. However, from the levels of other radioactive elements, this was not the case. Sequential extraction studies were performed on aerosols collected in Lithuania after dust storms in September 1992 carried radioactive aerosols to the region from contaminated areas of the Ukraine and Belarus. The fraction distribution of241 Am in the aerosol samples was approximately (fraction, percent) organically-bound, 18% oxide-bound, 10% acid-soluble, 36% and residual, 32% (Lujaniene et al. 1999). Very little americium was found in the more readily extractable exchangeable and water soluble and specifically adsorbed fractions. 

Shan and Chen [32] reported that various proportions of metals released from exchangeable, carbonate-bound iron, manganese oxide-bound and organic-bound fractions were readsorbed onto the other solid geochemical phases during sequential extractions. 

The metal phases which are presumed to be sequentially extracted are step 1, soluble, exchangeable and carbonate-bound metals step 2, metals occluded in easily reducible manganese and iron oxides step 3, organically bound metals and sulphides step 4 , metals in non-silicate minerals lattice structure. It is important to emphasise that these metal phases are nominal target only, operationally defined by the extraction used. Consequently, is highly desirable and recommended to refer to the sequentially extracted metal fractions as easily extractable , reducible , oxidi-sable and residual , respectively. 

Sediment samples on the other hand may be treated in different ways, depending on the information required. Water contained in sediments can be removed and analyzed by the same methods as for aqueous samples, but speciation information on the solid fraction is more difficult to acquire. Series of sequential extractions are already employed to acquire the information needed to understand the cycling of As in sediments, for example, on water-soluble, phosphate-exchangeable, organically-bound and residual phases in such media." Literature on extraction procedures for detection, hyphenated by chromatographic techniques, is much more recent extractions of... 

Figure 9. Geochemistry of P with age at Sites 1033 (a) and 1034 (b). The geochemical fractionation was performed via a sequential extraction technique (Ruttenberg 1992, Filippelli and Delaney 1996, Anderson and Delaney 2000), which separates reducible and adsorbed phases (P red), authigenic phases (likely CFA-P auth), organically-bound P (P org) and detrital P (P detr). Note an overall decrease in the reducible and organic fractions and an increase in the authigenic fraction in the older sediments.

Shuman (1982, 1985), working on the speciation of Cu, Mn, Fe and Zn, modified the sequence of the extraction as exchangeable, oxidizable (organically bound), easily reducible (Mn oxides-bound), moderately reducible (amorphous Fe oxides-bound), strongly reducible (crystalline Fe oxides-bound), and residual. The low percentages of the oxidizable fractions obtained following the sequential extraction scheme of Shuman (1985) as compared to those obtained following the scheme of Tessier et al. (1979) were attributed to the lack of selectivity of the method used (Charlatchka et al, 1997). 

Results of the five-step sequential extraction are presented in Fig. 2, which illustrates the distrihution of exchangeable (Exc.), carbonate-associated (Car.), Fe-Mn oxides-bound (Oxi.), organic-bound (Org.) and residual (Res.) metals found in the soil sample. 

Bound residnes are those chemicals retained in the subsurface matrix in the form of the parent organic contaminant or its metabolites these residnes remain after subsequent extractions, dnring which the nature of the compound or of the matrix is not altered by the extraction procedure. An example of sequential extraction of... 

Johnston AE, Goulding KWT, Poulton PR (1986) Soil acidification during more than 100 years under permanent grassland and woodland at Rothamsted. Soil Use Manage 2 3-10 Kahn SU (1982) Bound pesticides residues in soil and plant. Residue Rev 84 1-25 Kan AT, Chen W, Tomson MB (2000) Desorption kinetics from neutral hydrophobic organic compounds from field contaminated sediment. Environ Pollution 108 81-89 Kang SH, Xing BS (2005) Phenanthrene sorption to sequentially extracted soil humic acids and humans. Environ Sci Technol 39 134-140... 

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