Sediments sequential extraction

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... 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

Ruttenberg, K. C. (1992). Development of a sequential extraction method for different forms of phosphorus in marine sediments. Limnol. Oceanogr. 37, 1460-1482. 

Thomas, R. R, Ure, A. M., Davidson, C. M., Littlejohn, D., Rauret, G., Rubio, R., and Lopez-Sanchez, J. F., Three-Stage Sequential Extraction Procedure for the Determination of Metal in River Sediments, Analytica Chimica Acta 286, 1994, 423 29. 

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... 

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. 

Mahan K.I., Foderaro T.A., Garza T.L., Martinez R.M., Maroney G.A., Trivisonne M.R., Willging E.M. Microwave digestion techniques in the sequential extraction of cadmium, iron, chromium, manganese, lead and zinc in sediments. Anal Chem 1987 59 938-945. 

Rapin F., Tessier A., Campbell P.G.C., Carignan R. Potential artifacts in the determination of metal partitioning in sediments by a sequential extraction procedure. Environ Sci Technol 1986 20 836-840. 

Shannon R.D., White J.R. The selectivity of a sequential extraction procedure for the determination of iron oxyhydroxides and iron sulfides in lake sediments. Biogeochem 1991 14 193-208. 

Keon, N.E., Swartz, C.H., Brabander, D.J., Harvey, C., Hemond, H.F. 2001. Validation of an arsenic sequential extraction method for evaluating mobility in sediments. Environmental Science and Technolology, 35, 2778-2784. 

Whalley C, Grant A. Assessment of the phase selectivity of the European Community Bureau of Reference (BCR) sequential extraction procedure for metals in sediment. Anal. Chim. Acta 1994 291 287-295. 

Mossop KF, Davidson CM. Comparison of original and modified BCR sequential extraction procedures for the fractionation of copper, iron, lead, manganese and zinc in soils and sediments. Anal. Chim. Acta 2003 478 111-118. 

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. 

Tiyapongpattana, W., Pongsakul, P., Shiowatana, J., and Nacapricha, D. (2004). Sequential extraction of phosphorus in soil and sediment using a continuous-flow system. Talanta 62 765-771. 

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... 

R. Santamaria-Fernandez, A. Moreda-Pineiro and S. J. Hill, Optimisation of a multielement sequential extraction method employing an experimental design approach for metal partitioning in soils and sediments, J. Environ. Monit., 4(2), 2002, 330-336. 

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. 

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. 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. For example, selective sequential extraction procedures are used to isolate metals associated with the water/acid soluble , exchangeable , reducible , oxidisable and residual fractions in a sediment. The reducible, oxidisable and residual fractions, for example, are often equated with the metals associated, bound or adsorbed in the iron/manganese oxyhydroxide, organic matter/sulfide and silicate phases, respectively. While this is often a convenient concept it must be emphasised that these associations are nominal and can be misleading. It is, therefore, sounder to regard the isolated fractions as defined by the operational procedure. Physical procedures such as the division of a solid sample into particle-size fractions or the isolation of a soil solution by filtration, centrifugation or dialysis are also examples of operational speciation. Indeed even the distinction between soluble and insoluble species in aquatic systems can be considered as operational speciation as it is based on the somewhat arbitrary definition of soluble as the ability to pass a 0.45/Am filter. 

Single and sequential extraction schemes have been designed in earlier years and widely used to assess the different retention/release of metals in soil and sediment samples (Tessier et al., 1979 Salomons and Forstner, 1980 Thomas et al., 1980 Meguellati et al., 1987). However, the lack of uniformity in the different procedures used did not allow the results to be compared worldwide or the procedures to be... 

This chapter considers methods of trace element speciation, and their application to soils, that involve selective chemical extraction techniques. It will be concerned firstly with extraction by single selective reagents and secondly with the development and application of sequential extraction procedures for soils and related materials. Sequential extraction procedures for sediments are discussed in depth in Chapter 11. Speciation in the soil solution and modelling aspects of its interaction with soil solid phases are comprehensively covered in Chapter 9 and will not be considered here. 

Sequential extraction involves treatment of a sample of soil or sediment with a series of reagents in order to partition the trace element content. The reagents used are generally similar to those employed as single extractants to liberate metals bound to particular components of the sample matrix, discussed above. The growth in popularity of the approach is demonstrated by the marked increase in publications in which it has featured over the past decade (Fig. 10.2). 

Various workers have questioned the ability of sequential extraction to provide accurate information on the mineralogical phases with which trace elements are associated in soil or sediments (e.g. Nirel and Morel, 1990). Problems, including non-selectivity of reagents and readsorption of analytes following release, are frequently reported. Hence, nowadays, most environmental analytical chemists accept that sequential extraction should be considered an operational form of speciation, in which the fractions isolated are defined purely by the sequence of reagents used, and not as a means to determine information on the specific mineralogical phases to which trace elements are bound. Modern sequential extraction procedures label the fractions obtained in terms of the type of chemical reaction used to isolate them, in order to emphasise this, e.g. reducible or oxidisable species. Unfortunately, this distinction is not always made clear in the wider environmental literature. 

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). 

Sediment obtained from several sites in Lake Flumendosa, Italy, was collected, homogenised and, following a certification campaign, became available as BCR CRM 601 lake sediment certified for its extractable trace metal contents -sequential extraction (Quevauviller et d., 1997). In sediment CRM 601, concentrations of extractable Cd, Cr, Ni, Pb and Zn are certified in Step 1, but only Cd, Ni and Zn in Step 2, and Cd, Ni and Pb in Step 3. Indicative values are also given for extractable Cu in Step 1 and Pb in Step 2 (European Commission, 1997). The long-term stability of the extractable trace metal content of the reference material was recently demonstrated in a European intercomparison exercise (Lopez-Sanchez, 1998). 

A modified BCR sequential extraction was recommended based on this work, and its performance compared with the original BCR procedure via an interlaboratory trial (Rauret et al, 1999). Improved reproducibility was obtained. A new sediment reference material CRM 701 has been certified for metals extractable by the modified BCR procedure (Pueyo et al., 2001). The modified extraction protocol is given in the Appendix. It is important to emphasise that extractions should be performed exacdy as described if results comparable with other users are to be obtained. 

The reference materials currendy certified for metals extractable by a sequential extraction procedure are BCR CRM 601 and BCR CRM 701. The lack of reference materials in this area has prompted many workers to apply sequential extraction to other reference soils and sediments, certified for total metal contents, in an attempt to provide interim data useful in method validation. 

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. 

The impact of heavy metals from highways on adjacent soils and receiving waters has also been investigated by sequential extraction (Stone and Marsalek, 1996). Airborne dust, at least partly derived from motorways, was found to be a significant source of soil contamination in two satellite cities of Seoul, South Korea (Chon et al., 1998). A comparison between roadside soil and sediment from... 

A further area in which sequential extraction continues to be applied successfully is in assessment of the likelihood of mobilisation of metal contaminants from sediment-derived soil. When dredged sediment is used to reclaim land from the coastal margins or applied to arable soil to improve fertility, there is concern that potentially toxic elements accumulated under reducing conditions may be released on exposure to an oxygen-rich environment. Sequential extraction can be used to characterise the sediment prior to application, or to monitor changes in metal availability in the soil with time (e.g. Singh et al, 1998). 

Sequential extraction is now a well-established tool in soil and sediment analysis. Although the approach is unlikely to provide precise information on the mineral phases to which trace metals are bound, it does provide useful information on potential mobilities of heavy metal contaminants which is not available from (pseudo)total metal determination. The adoption of standard protocols, such as that recommended by BCR, means that reliable and comparable data can be obtained by different laboratories. 

Borovec, Z. (1996) Evaluation of the concentrations of trace elements in stream sediments by factor and cluster analysis and the sequential extraction procedure. Sci. Total Environ., 177, 237-250. 

Coetzee, P.P., Gouws, K., Pluddemann, S., Yacoby, M., Howell, S. and Drijver, L. den (1995) Evaluation of sequential extraction procedures for metal speciation in model sediments. Water SA, 21, 51-60. 

European Commission (1997) The certification of the extractable contents (mass fractions) of Cd, Cr, Ni, Pb and Zn in sediment following a three-step sequential extraction procedure (CRM 601). Report EUR, EN 17554, ISBN 92-828-0127-6. 

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. 

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