Since their introduction in the late 1970s, sequential extraction procedures have experienced a rapid increase in use. They are now applied for a large number of potentially toxic elements in a wide range of sample types. This review uses evidence from the literature to consider the usefulness and limitations of sequential extraction and thereby to assess its future role in environmental chemical analysis. It is not the intention to provide a comprehensive survey of all applications of sequential extractions or to consider the merits and disadvantages of individual schemes. These aspects have been covered adequately in other, recent reviews. This review focuses in particular on various key issues surrounding sequential extractions such as nomenclature, methodologies, presentation of data and interpretation of data, and discusses typical applications from the recent literature for which sequential extraction can provide useful and meaningful information. Also covered are emerging developments such as accelerated procedures using ultrasound- or microwave energy-assisted extractions, dynamic extractions, the use of chemometrics, the combination of sequential extraction with isotope analysis, and the extension of the approach to non-traditional analytes such as arsenic, mercury, selenium and radionuclides.

Is there a future for sequential chemical extraction

A comprehensive review of the single and sequential extraction schemes for metal fractionation in environmental samples such as soil and industrially contaminated soils, sewage sludge and sludge amended soils, road dust and run off, waste and miscellaneous materials along with other approaches of sequential extraction methods are being presented. A discussion on the application of chemometric methods in sequential extraction analysis is also being given. The study of single and sequential extraction methods for various reference materials are also being looked into. The review covers several aspects of the single and sequential extraction methodologies. The use of each reagents involved in these schemes are also discussed briefly. Finally the present upto date information by different workers in various fields of environmental geochemistry along with the possible future developments are also being outlined.

A Review of the Different Methods Applied in Environmental Geochemistry For Single and Sequential Extraction of Trace Elements in Soils and Related Materials

It is important to evaluate different digestion methods to accurately determine elemental concentrations in soils. Three commonly used digestion procedures, hotplate aqua regia, microwave aqua regia, and microwave aqua regia + HF, were compared for digestion of three standard reference materials (SRMs 2704, 2709, and 2711) and 20 Florida soils (three groups of Quartzipsammemts, one group of Alaquods, and one group of Paleudults). Sixteen elements (Al, Ba, Ca, Fe, K, Mg, Mn, P, Zn, As, Cd, Cr, Cu, Ni, Pb, and Se) were analyzed using either an inductively coupled plasma optical emission spectrometer (ICP-OES) or a graphite furnace atomic absorption spectrophotometer (GFAAS). Precise analysis was achieved for all elements except As (1.0-25%), Cd (1.8-22%), and Se (4.1-22%) in the SRMs using all three procedures, with the microwave aqua regia + HF procedure having slightly better precision (3.7%) averaged across all elements. Compared with the elemental recoveries in SRMs by the microwave aqua regia digestion (80%), microwave aqua regia + HF digestion achieved greater accuracy (94%), whereas the hotplate aqua regia digestion achieved less accuracy (74%). In general, the microwave aqua regia + HF digestion was overall the best procedure for determining concentrations of most metals in SRMs and Florida soils, followed by the microwave aqua regia and the hotplate aqua regia digestion. However, this so-called total-total digestion procedure (microwave aqua regia + HF) may underestimate total Pb concentration in Florida soils and total Al, Ca, Fe, Mg, and Ba concentrations in the Florida Paleudults.

Comparison of Three Aqua Regia Digestion Methods for Twenty Florida Soils

A glance into aluminum toxicity and resistance in plants.

Use of the modified BCR three-step sequential extraction procedure for the study of trace element dynamics in contaminated soils

Utilization of optimized BCR three-step sequential and dilute HCl single extraction procedures for soil-plant metal transfer predictions in contaminated lands.

Green algae, especially Cladophora species, are generally considered as the best bioindicator of aquatic bodies contamination by nutrients as well as by heavy metals. Therefore, the object of this study was to investigate to which extent toxic metals (Ni, V, Cd, Pb, Cr) are present in algal biomass and to establish the bioaccumulation coefficients in correlated algae / water environments in a sewage lagoon, which represents the tertiary stage of a refinery waste water treatment plant (Slovnaft, Bratislava). Due to the orographic depression between the Eastern Alps and Western Carpathians and the characteristic atmospheric circulation with predominance of NW wind direction, the deposition of heavy metal aerosols from closed industrial activities is expected to contribute to bioaccumulation capacities of algae for these elements. The water of the refinery sewage lagoon has been monitored for BOD, COD, petroleum hydrocarbons, pH, BTX, halogenated hydrocarbons, some polyaromates, phosphates, ammonium, sulfates and suspended matter. From the viewpoint of heavy metal contents in agricultural composts, a management scenario for algal biomass reutilization, i.e. recycling nutrients and proteins back into the biosphere, via compost processing, is proposed.

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Bioaccumulation of heavy metals by green algae cladophora gramerata in a refinery sewage lagoon

An optimised BCR three steps sequential extraction procedure (BCR SEP) and several single extractions with KCl, NH(4)Cl, Na(4)P(2)O(7) and 0.5 mol L(-1) HCl were used for the fractionation of Al, Cu, Fe, Mn, Pb and Zn in CRMs and in samples from a mining area with sulphidic deposits. A good interlaboratory comparability was obtained for Cu, Pb and Zn in CRM 483, CRM 701, SRM 2710 and SRM 2711 by BCR SEP. The reliability of the results obtained is also very satisfactory. Some differences were found between our results and the indicative data for Al and Fe fractionation. However, serious discrepancies were found for Mn, not only for individual steps of the fractionation, but for the data obtained overall (sum of 1-3 steps), and for the total concentration as well. Our results could be utilized as a contribution to the existing indicative values for CRM 483, SRM 2710 and SRM 2711 for interlaboratory study. Moreover, data for the fractionation of elements mentioned above for CRM 701 are first presented here.A high correlation between 0.5 mol L(-1) of HCl-extractable amounts of the elements studied, and the sum of the three steps of BCR SEP in acid sulphatic weathering products and naturally acidified soils was established, which allows us to suggest this rapid and cost-effective single extraction procedure as a valuable tool in contamination assessment.

Ján Medved

Papers

Utilization of optimized BCR three-step sequential and dilute HCl single extraction procedures for soil-plant metal transfer predictions in contaminated lands.

Bioaccumulation of heavy metals by green algae cladophora gramerata in a refinery sewage lagoon

Fractionation of various elements in CRMs and in polluted soils

Determination of lead and cadmium in human hair by atomic absorption spectrometric procedures after solid phase extraction

Free aluminium extraction from various reference materials and acid soils with relation to plant availability.