Sequential extraction studies

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. 

Some work on sediments is reported here in the belief that it may also be useful in the analysis of soil samples. Thus Asikainen and Nikolaides [33] have carried out a sequential extraction study of chromium from contaminated aquifer sediments and found that 65% of the chromium was extractable. Of this amount 25% was exchangeable, 11% was bound to organic matter and 30% was bound to iron and manganese oxide surfaces. Thomas et al. [34] also investigated the use of BCR sequential extraction procedures for river sediments, and found the method to work well. Real et al. [35] improved sequential extraction by optimising microwave heating. 

Arunachalam, J., Emons, H., Krasnodebska, B. and Mohl, C. (1996) Sequential extraction studies on homogenised forest soil samples. Sci. Total Environ., 181, 147-159. 

Table 7 shows a summary of the findings of various sequential extraction studies on contaminated soils. The data from individual studies in Table 7 are averages of soil from more than one source. No studies of artificially spiked soils have been included, because they exhibit very different behaviour to waste site soils (Tuin Tels 1990). Despite the wide range of soil and contaminant sources included in Table 7 some clear trends are apparent. For example, extractable copper is mainly associated with the oxidiz-able phase, which may indicate that it is bound to organic matter (Cu can be strongly bound by soil organic matter Baker Senft 1995). 

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

In the present work it has been shown that on-line coupling of flowthrough fractionation in RCC with ICP-EAS detection enables not only the fast and efficient fractionation of trace elements (TE) in environmental solids to be achieved but allows real-time studies on the leaching process be made. A novel five-step sequential extraction scheme was tested in on-line mode. The optimal conditions for the fractionation were chosen. Investigating elution curves provides important information on the efficiency of the reagents used, the leaching time needed for the separation of each fraction, and the potential mobility of HM forms. 

Ahnstrom and Parker (2001) studied Cd reactivity in metal-contaminated soils using a coupled stable isotope dilution-sequential extraction procedure. They found that in uncontaminated arid soil and in... 

Badri M.A., Aston S.R. A comparative study of sequential extraction procedures in the geochemical fractionation of heavy metals in estuarine sediments. International Conference Amsterdam, pp 705-708. 1981. 

In this study, 30 soil samples from rice farmland in Zhejiang province, in eastern China. We sampled the cultivation layer soils during rice harvest season. The soils are acidified and the average value of pH is 5.82. A sequential extraction procedure... 

Gleyzes C, Tellier S, Astruc M. Fractionation studies of trace elements in contaminated soils and sediments a review of sequential extraction procedures. TrAC Trend Anal. Chem. 2002 21 451—467. 

Much work has been reported on the evaluation of sequential extraction procedures. The three-stage sequential extraction procedure for speciation of heavy metals proposed by the Commission of the European Communities Bureau of References (BCR) was found to be acceptable and reproducible with some modifications [29]. In another study, when applied to real soils and sediments, this (unmodified) BCR method was queried [30]. Lopez-Sanchez et al. [31 ] found that significant results can be obtained when different sequential extraction procedures are used. 

The sequential extraction of chromium from soils has been studied [89]. A three-step sequential extraction scheme has been proposed using acetic acid, hydroxylamine hydrochloride and ammonium acetate as extracting agents. Steps 1 and 2 were measured by electrothermal atomic absorption spectrometry (ETAAS). Step 3 was measured by flame atomic absorption spectrometry. Interfering effects when measuring chromium in soils were circumvented through the use of a 1% 5-hydroxyquinoline suppressor agent. 

Campbell et al. (1967) applied sequential extraction to characterize FA, HA, and humin from gray podzolic and chemozemic soils. The fractions of FA and HA extracted by 0.5 M NaOH without acid pretreatment, which they called mobile humates (since the researchers assumed that they are not bound to minerals), had a lower mean residence time (ranging from 85 to 785 for HA, respectively, in the chernozemic and gray podzolic soils) as compared to Ca-humates extracted from humin (1410 years in the chemozemic soil) and to the total FA and HA extracted after acid pretreatment (195-1235 years for HA). This study showed that in the chernozemic soil, Ca-humates and clays play an equally important role in the stabilization of HS, whereas in the podzolic soil the oldest fraction was associated with clays. 

The philosophy and limitations of sequential extraction are described in detail in Chapter 11, where the use of the approach in sediment research is also reviewed. Although originally developed for application to sediments, sequential extractions have since been applied successfully in many soil studies. Recent work... 

Recently, a group of experts working under the auspices of the Commission of the European Communities, Community Bureau of Reference (BCR) sought to improve comparability between sequential extraction results obtained by different laboratories, and proposed a simple, three-stage sequential extraction procedure for sediment (Table 10.3) (Ure et d., 1993a, b). The protocol was then refined through two sets of interlaboratory trials (Quevauviller et d., 1994) and studies were conducted to assess whether adequate homogeneity and stability could be achieved to allow certification of a reference material for metals extractable by the procedure (Fiedler et d., 1994). 

In common with other sequential extraction procedures, the BCR scheme suffers from a degree of non-specificity (Whalley and Grant, 1994 Coetzee et d., 1995) and redistribution of analytes during extraction (Raksasataya et d., 1996). Some success in limiting lead redistribution by addition of cryptand 2.2.2 or nitriloacetic acid to the acetic acid in Step 1 has been reported, but the effectiveness of the complexing agent was found to be strongly dependent on the bulk composition of the model soil system studied (Raksasataya et d., 1997). 

A major limitation to the widespread adoption of sequential extraction for trace element speciation is the lengthy sample processing time (e.g. three 16-h periods of mechanical shaking for the BCR method). Various authors have attempted to develop more rapid means of extraction, involving ultrasonic or microwave assistance. The goal of such studies is generally to obtain performance similar to... 

Chemometrics can also be used to overcome some of the intrinsic deficiencies of sequential extraction, such as non-specificity. Barona and Romero (1996a) used principal components analysis (PCA) to establish relationships between the amounts of metals released at each stage of a sequential extraction procedure and bulk soil properties, and demonstrated that carbonates played a dominant role in governing metal partitioning in the soil studied. The same workers employed multiple regression analysis to study soil remediation (see Section 10.11.1.1). Zufiaurre et al. (1998) also used PCA to confirm their interpretation of phase association and hence potential bioavailability of heavy metals in sewage sludge. 

The effect of amending soil with other types of organic-rich material has also been investigated by sequential extraction. These materials include chicken manure and cowpea leaves (Li et al, 1997) spent mushroom compost, commercial humic acid and poultry litter (Shuman, 1998) and cow manure, pig manure and peat soil (Narwal and Singh, 1998). The mechanisms by which inorganic additives (zeolite, apatite and iron oxide) reduce uptake of Cd and Pb by crops have also been studied (Chlopecka and Adriano, 1997). 

The behaviour of landfill liners with respect to metal sorption has also been investigated by the novel technique of combined sequential extraction-sorption isotherm analysis (CSSA) (Salim et al, 1996). The study demonstrated that Pb and Ni would be effectively immobilised by the clayey calcareous sediment studied, but Cr would not. Roehl and Czurda (1998) applied a similar approach in their investigation of clay landfill liners and showed that speciation was dependent on heavy metal load, with weaker binding at higher concentrations of Cd and Pb. 

Copper, lead, cadmium and zinc have been found predominantly in potentially mobile forms by sequential extraction of material collected during road cleaning (Colandini et al, 1995). Cadmium and zinc were found to be more labile than lead and copper. A study of street dust and gully pot sediments confirmed this order of potential availability (Striebel and Gruber, 1997) and also suggested that lead levels in material of the types studied had decreased since the introduction of unleaded fuel in Germany. Lead has also been studied in street dusts from Brisbane, Australia. The element was found mainly in the carbonate phase and in the smaller particle size fraction (Al-Chalabi and Hawker, 1996) except where resuspension caused particle aggregation. 

Campos, E., Barahona, E., Lachica, M. and Mingorabce, M.D. (1998) A study of the analytical parameters important for the sequential extraction procedure using microwave heating for Pb, Zn and Cu in calcareous soils. Anal. Chim. Acta, 369, 235-243. 

Fiedler, H.D., Lopez-Sanchez, J.F., Rubio, R., Rauret, G., Quevauviller, Ph., Ure, A.M. and Muntau, H. (1994) Study of the stability of extractable trace metal contents in a river sediment using sequential extraction. Analyst, 119, 1109-1114. 

Userno, J., Gamero, M., Morillo, J. and Gracia, I. (1998) Comparative study of three sequential extraction procedures for metals in marine sediments. Environ. Int., 24, 487-496. 

---