Sequential extraction experiments

Sequential extraction experiments have been shown to provide a convenient means to determine the metals associated with the principal accumulative phases in sedimentary deposits, to elucidate the mechanisms of their diagenetic transformation, and to elucidate release processes upon changing environmental conditions (Kersten and Forstner, 1989). A general goal of all studies involving selective chemical extraction is the accurate determination of partitioning of elements of environmental concern among different discrete phases of a sample. 

Brady et al. (2003) proposed that a site-specific screening approach followed by sequential extraction measurements could be an appropriate method to determine if a contaminated site is suited for MNA. In the first step, the site s chemical and hydrological conditions are assessed from standard site characterization data. The MNAtoolbox (www.sandia.gov/eesector/gs/gc/na/mnahome.html) provides a rapid initial assessment of the chemical and hydrologic conditions for MNA. The site-specific assessment for natural attenuation is then evaluated using sequential extraction experiments that enhance the site s characterization, determine the hioavailability, fate, and transport of the metal(loid)(s) in question, and assess natural attenuation against other remediation options (such as phytoremediation). 

From results obtained by sequential extraction experiments, as well as from measurements of radioactivity of samples from Fruska Goia National Park, it can be concluded that ... 

Table I. Kesttlts of the V isotope exchange experiments f Fig. I) and of the sequential extraction es/ieriments of Del Nero et al. (1999a), using Bangombe samples collected in the weathered pelites (6.2 and 6.B) and in the Fe-crust (10.3)...

Just choosing the most widely applied procedure (namely that of Tessier et al., 1979) could yield data of doubtful reliability for a particular matrix or objective, but may nevertheless allow comparison with results of many other studies. In practice, there is always an optimisation necessary between compatibility and reliability. The limitations reported here and elsewhere lead to the conclusion that results given by sequential sediment extraction experiments can be used for an assessment of specific release scenarios particularly related to changing pH, complexing ligand availability and redox environments rather than for true metal speciation in sediments. The latter can be achieved only by using intrumental speciation techniques, either alone or in combination with sequential extraction. It is in this area of research that new developments have appeared since the first edition of this volume. Particularly... 

The results of sequential leaching experiments and the bioaccumulation studies reveal a selective assimilation of certain chemical forms of some trace metals by molluscs. There seems to be a relationship between seawater-soluble chromium levels and accumulation of the element in the kidneys of exposed bivalves. Particulate forms of chromium, while present in the digestive glands, do not appear to have been assimilated by the organisms, even though much of the total chromium was dissolved by a relatively mild extractant -25% acetic acid. Thus, an estimation of the bioavailability of particulate metals based on their solubility in dilute acetic acid can be erroneously high, at least for herbivorous filter feeders. 

In Chapter 3.4 a method has been presented for long-term prognosis of metal pollutant mobility, which combines column circulation leaching experiments at variable pH/E -conditions with sequential extraction procedures on the solid waste material before and after these experiments (Schoer FSrstner, 1987). Temporal release patterns are different for the individual elements (Figure 6-5) While at pH 5/400 mV release of cadmium seems to be completed within the experimental period mobilization of copper is still going on and the end point cannot be estimated from the data of the "kinetic" experiments. The same effect has been found for the examples of thallium and vanadium. For the other elements, the endpoint of release can be determined as approximately 10 mg cobalt, 0.6 mg cadmium, 600 mg zinc and 0.3 mg chromium, 2 mg barium and 20 mg lead (per 100 g of solid substrate treated with 140 L solu-... 

In spite of intensive investigations (sequential extractions and specific extractants) on prediction of the availability of trace metals, there are still not easy and good estimates of the general bioavailability of a given trace element. However, based on results of long-term experiments, some specific extractants - as well as weak neutral salt solutions - seem adequate to assess... 

The primary objective of this study was to investigate the fractionation of copper, cadmium and lead in the rhizosphere soil in an attempt to obtain a better understanding of their availability and subsequent uptake by plants. In this regard, the present chapter focuses on (1) root-induced changes in various fractions of copper, cadmium and lead in the maize rhizosphere using rhizobox and sequential extraction techniques and (2) influences of pH, root exudates and microbial activity on metal fractionation in the rhizosphere of maize, wheat, pea and soybean, based on the results of specially designed experiments. 

An investigation of toxicity of scrap tires leachates in estuarine salinities was conducted by Hartwell et al. [31] to determine if tires are acceptable for artificial reefs. It was found that tire leachates are toxic to some marine species and their toxicity varied inversely with salinity. Toxic effects were not apparent at 25%o salinity. This may be due to differential leachability of toxic chemicals, differential interaction of salts and toxicants, and an effect of salinity on tolerance of the organism, or some combination of these factors. Toxicity diminished substantially with sequential extraction and quickly, rather than gradually and steadily over several weeks. Similar results were observed in freshwater experiments [ 32 ]. The toxicity values do not suggest a substantial threat by tire reefs to water quality. The use of tires in higher salinity environments appears to pose little direct toxicological risk to resident organisms. However, bioaccu-mulative effects are possible. 

Combining both heating and nonheating protocols employed in a sequential order were evaluated, but without any advantage (Fig. 3.4). RT-PCR was performed by standard methods, RNA extracted from fresh MDA cells and human tissue of breast cancer with known tested genes was used as positive control, and pure water was used to replace template (cDNA) as negative control for every experiment of PCR. To assure the accuracy of PCR tests, all reactions were performed in triplicate. 

The reaction catalyzed by KDO 8-phosphate synthetase (reaction 2, Scheme 35) was first observed by Levin and Racker9 in extracts from Pseudomonas aeruginosa (see Scheme 1), and later by Ghalambor and Heath29 in extracts from Escherichia coli 0111 B4 and J-5. In the initial experiments of Levin and Racker,135 the fate of D-ribose 5-phosphate in crude bacterial extracts was studied, and the KDO 8-phosphate discovered by the authors is really derived from D-ribose 5-phosphate by three, sequential, enzyme-catalyzed reactions (see Scheme 36). 

The MS analysis using ESI was applied for the determination of an unknown surfactant compound contained in an extract of a shampoo formulation [44]. MS leading to sequential product ions helped to identify the constituents. The MS4 experiments together with other spectral observations confirmed the hypothesis that the unknown compound was a N-( 2-aminoethyl) fatty acid amide with the general formula R-C(0)-NH(CH2-CH2-N)R/R,/. An authentic sample of the proposed laury ampho mono acetate (LAMA) (R = -CH2-CH2-OH and R" = -CH2-CH2-COOH) that was available led to the same [M + H]+ parent ion at m/z 345. The fragmentation that could be observed under ESI-FIA-MS-MS(+) conditions resulted in an intensive examination of amide surfactants. However, only two of them—lauryl diethanol amide ([M + H]+ m/z 288), a non-ionic surfactant and laurylamido-(3-propyl betaine ([M + H]+ m/z 343)—... 

PUF, unlike other polymeric sorbents, tends to be a nonhomoge-neous product containing a number of additives and artifacts in variable quantities from lot to lot. Our experience, however, indicates that these contaminants can be sufficiently reduced to permit trace organic analysis by employing a sequential solvent extraction procedure in conjunction with stringent quality control criteria prior to actual use. This observation is consistent with the experience of other investigators who have used flexible foams extensively in analytical environments. 

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