Elemental fractionation of Si, Al, Ti, Fe, Ca, Mn, P, and Ba in five marine sedimentary reference materials: results from sequential extractions

The geochemical and environmental characteristics of trace metals in surface sediments of the river estuarine mouths around the Taiwan Island and the Taiwan Strait

The trace metals species in surface sediments of the Taiwanese river estuarine mouths and the Taiwan Strait were examined by sequential extraction method. Based on the metal species present in sediments, trace metals can be divided into three groups: (1) Co, Cr, Fe, Ni and Zn; (2) Cu and Hg; and (3) Mn and Pb. The total concentrations of trace metals in the first two groups are dominated by the residual fraction. While, Cu and Hg their organic species also contributes a significant percentage and reduces the residual fraction portion. Lead and Mn are dominated by the labile fraction. The total metal concentrations in the analyzed sediments seem to be influenced by Fe oxides, TOC and grain size. The metals contamination status assessed by three environmental indices suggests that the analyzed sediments are minor contaminated by trace metals, with a few exceptions of Cu and Hg at some stations.

Investigation of metal mobility in gold and silver mine tailings by single-step and sequential extractions

Metal leachate from mine tailings has the potential to release toxic metals into the surrounding environment. A single-step extraction procedure mimicking rainwater and a three-step BCR sequential extraction procedure (acid, reducing and oxidizing conditions) were applied to gold (GMT) and silver (SMT) mine tailings. Major (Al, Ca, Fe, Mg, and Mn) and trace metals were monitored to better understand the mobility and geochemistry of these metals when exposed to various environmental leaching conditions. Rainwater extraction released only small quantities of metals, while the three-step BCR extraction was more effective in mobilizing metals from the tailings. Under the acidic conditions of BCR step 1, Ca, Mg, Cd, Cu, and Mn were released in high concentrations. The dissolution of Fe, Ca, and Mg were dominant along with Pb in step 2 (reducing conditions). In step 3 (oxidizing conditions), Fe was the most dominant species together with Co, Cu, Ni, and Se. A high fraction of Al, Be, Cr, Li, Mo, Sb, Tl, and V remained in the residue. From SMT, larger quantities of As, Ca, Cd, and Zn were released compared to GMT. The BCR extraction could be applied to tailings to predict the potential release of toxic metals from mine wastes; however, excessive amounts of Ca and Fe in the tailings could cause carry-overs and incomplete extraction and carry-overs, resulting in a misinterpretation of results.

Distribution of Geochemical Species of P, Fe and Mn in Surface Sediments in the Eutrophic Estuary, Northern Taiwan

The Danshuei River Estuary (DRE) in northern Taiwan is a seriously eutrophic estuary due to the domestic effluent discharge. Surface sediment samples were collected from the DRE to study the concentrations and spatial distributions of different fractions of phosphorus through the five-step sequential extraction method which chemically divides the sedimentary P into five fractions: PSORB, PCDB, PCFA, PDET, and PORG. The Fe and Mn contents in the extracted solution were also determined. The total organic carbon (TOC) and grain size in sediment samples were analyzed as well. The sedimentary total P (TP) concentrations ranged within 537–1310 mg/kg and mostly exceeded 800 mg/kg, suggesting that the DRE sediments were moderately polluted by phosphorus. The PCDB was the dominant fraction of P, averagely contributing 58% of TP, followed by PDET 31%. The contributions of the PSORB and PCFA fractions to the TP were relatively minor. Two fractions, FeCDB and FeORG, of sedimentary Fe equally shared approximately 70% of total Fe, followed by FeDET with 22%. The contribution of different fractions of sedimentary Mn followed the sequence: MnCDB (36%) > MnCFA (29%) > MnORG (14.7%) > MnDET (14.5%) > MnSORB (5.3%). The sedimentary P, Fe, and Mn within the DRE are easily mobilized because they were mainly present in the reducible fraction. The concentrations of sedimentary TP positively correlated with the TOC contents and inversely negatively correlated with grain size, suggesting that the TOC and grain size play the crucial roles in influencing the distribution of sedimentary P within the DRE. Finally, the Fe(III) (hydro)oxides seems to play an important carriers to adsorb dissolved P because PCDB positively correlated with FeCDB.

Determination of 27 metals in HISS-1, MESS-4 and PACS-3 marine sediment certified reference materials by the BCR sequential extraction

The BCR sequential extraction procedure developed by the European Community Bureau of Reference was applied to the three marine sediment certified reference materials (CRMs). These CRMs are designated as HISS-1, MESS-4, and PACS-3 and comprise respectively pristine, moderately-contaminated, and highly-contaminated sediments, respectively. The study aimed to provide values of extractable elements in reference materials of varied geological origin to support method development and quality control efforts. Concentrations of 27 elements extracted in the three sequential extraction steps and in the residue were determined. The extraction steps consisted of: Step 1 - acetic acid extraction (targeting the exchangeable, water- and acid-soluble fraction); Step 2 - hydroxylammonium chloride extraction (targeting the reducible fraction); and Step 3 - hydrogen peroxide extraction (targeting the oxidizable fraction). The results from two independent laboratories using the sequential extraction procedure for the 27 elements were combined using the DerSimonian-Laird method of analysis implemented in the NIST Consensus Builder software. The percent recovery (sum steps vs total metal content) of 27 elements ranged from 68% to 125% in HISS-1, 76%-119% in MESS-4, and 70%-125% in PACS-3, based on the certified values. The combined uncertainty (k = 2) was from 1% to 39% for HISS-1, 3%-45% for MESS-4, and 3%-21% for PACS-3. Comparing the three extraction steps, the uncertainty of Step 3 was the highest for all the three CRMs. The agglomerate sediments in MESS-4 resulted in high uncertainty when compared to HISS-1 and PACS-3. The method validation showed the BCR sequential extraction procedure can apply to other elements including As, Co, Li, Mn, and V.

Speciation of potentially mobile Si in Yangtze Estuary surface sediments: estimates using a modified sequential extraction technique

To improve our understanding of the Si-related biogeochemical processes that occur in estuarine ecosystems with large subaqueous deltas (e.g., the Yangtze Estuary; YE), the speciation of Si in the surface sediments of the YE was investigated. The relationships between the different Si species and sediment bulk parameters were also discussed. Based on modified sequential extraction method, we can successfully estimate the following five sedimentary potentially mobile Si pools: weak acid leachable Si (W-Si); Si bound to organic matter (H-Si); Si coprecipitated with amorphous Fe/Al oxides (O-Si); Si coprecipitated with crystalline Fe/Al oxides (Ouv-Si), and biogenic silica (B-Si). The total potentially mobile Si pool (T-Si) ranged between 1689.31 and 5487.10 μg/g, with high values observed in deltaic mud deposits. The Si fractions were closely correlated with grain size compositions, except for O-Si. In deltaic mud deposits, efficient loss of organic matters and recycling of Fe oxides probably resulted in the amorphous or poorly crystalline Fe oxides uncoupled with the clay fractions, and thus leading to the lack of correlation between O-Si and grain size. As compared with Ouv-Si, the O-Si should possess stronger mobility, which highlights the importance of quantifying the O-Si pool in deltaic sediments.

Is there a future for sequential chemical extraction?

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.