Sequential Extraction Technique Research Articles

Changes of soil phosphorus speciation along a 120-year soil chronosequence in the Hailuogou Glacier retreat area (Gongga Mountain, SW China)

The Hailuogou Glacier (Gongga Mountain, SW China) has been retreating in response to global warming. A soil chronosequence (Hailuogou Chronosequence) has developed in the retreat area, and a primary plant succession has developed on it. To investigate the changes of soil phosphorus (P) fractions along the young soil chronosequence in the cold and humid climate, soil samples were collected at seven sites of different ages (0 to 120years). In all soil samples, concentrations of total P and of different P fractions (Bioavailable P, Al/Fe-bound P (P bound by Al and Fe oxides or hydroxides), Ca-bound P, and residual P) were determined using a sequential extraction technique. Organic P was determined using the high temperature ignition method. For the youngest (0years, 12years) soils, P forms were dominated by residual P, and topsoil forms of Ca-bound P, Al/Fe-bound P, organic P, microbial biomass P and bioavailable P were less than 1.86%. From 30 to 120years, for the topsoil, concentrations of Ca-bound P and organic P gradually increased; the concentration of bioavailable P in surface soil also showed a trend of increase, with percentages of 5–11.5% to total soil P; the concentration of residual P decreased; the concentration of Fe/Al-bound P contributed less than 5% to total soil P at all sites. Ca-bound P and organic P were the dominant P fractions at the older sites (ages: 80 and 120years). Soil P bioavailability and solubility were influenced by the changes of pH, and concentrations of Fe and Al oxide and hydroxide. The variations of vegetation and microbial activity are also considered as the impact factors of soil P forms. In the later stage of soil development (80~120years), plenty of soil P was transformed into biomass P pool (299.3kgha−1).

Organic acids inhibit the formation of pyromorphite and Zn-phosphate in phosphorous amended Pb- and Zn-contaminated soil

Pyromorphite (PY) and some zinc phosphates (Zn-P) are very sparingly soluble minerals and hence can immobilize Pb and Zn in contaminated soils. However, mechanisms leading to the poor efficiency of PY and Zn-P formation in contaminated soils amended with P still remain unclear. We studied the influence of two low molecular weight organic acids (LMWOA) – oxalic acid and citric acid and diethylene triamine pentaacetic acid (DTPA) – in PY and Zn-P formation in a P-amended contaminated soil. Despite the high levels of metals (∼4% Pb and 21% Zn) in the study soil, the addition of up to 1% inorganic P transformed only up to 37% and 17% of the total Pb and Zn to PY and Zn-P, respectively. Semi-quantitative estimates from a linear combination fitting of X-ray absorption near edge spectra (LC-XANES fitting) showed that the formation of PY decreased from 37% to 3% of the total Pb in the presence of oxalic acid and the addition of 1% P. The reduced PY formation may be associated with the increase in organic-bound Pb from 9% to 54% and decrease in carbonate associated Pb from 42% to 12% with oxalic acid addition as indicated by a chemical sequential extraction (SE) technique. Citric acid seemed to have a less adverse effect in PY formation than oxalic acid. Our data also suggests both oxalic and citric acids have less adverse effects on the efficiency of Zn-P formation. From this study we conclude that the abundance of LMWOA in soil environments can be one factor contributing to the poor efficiency of P amendments practices to effectively immobilize Pb and Zn in metal contaminated soils.

Significant correlation of Cd, Cu, Pb and Zn in sediments and oysters (Saccostrea cucullata) collected from Qeshm Island, Persian Gulf, Iran

The relationships are evaluated between the heavy metal species in sediments and the accumulation by the soft tissues of Saccostrea cucullata collected from the northern and southern coasts of Qeshm Island, Persian Gulf. The sequential extraction technique was employed to fractionate the sediment into non resistant and resistant fractions. Data from sequential extractions indicated that the metals were mainly associated with the residual fraction at the north coast and with non residual fractions at the south coast. The results showed that the best correlations were observed between heavy metals concentrations in soft tissues and the fractions in the southern sediment. Note that the bioavailability of trace metals is influenced by the chemical characteristics and properties of the sediment. Therefore, the present results generally supported the use of soft tissues of S. cucullata as a more accurate biomonitoring organism for Cu, Pb and Cd in sediments from the southern coast of Qeshm Island, Persian Gulf.

PH dependent dissolution of sediment aluminum in six Danish lakes treated with aluminum

The possible pH dependent dissolution of aluminum hydroxides (Al(OH)3) from lake sediments was studied in six lakes previously treated with Al to bind excess phosphorus (P). Surface sediment was suspended for 2 h in lake water of pH 7.5, 8.5, or 9.5 with resulting stepwise increments in dissolved Al observed in all lakes. The amount of dissolved Al increased proportional to the sediment content of Al(OH)3 as quantified by a sequential extraction technique. Up to 24% of the sediment Al(OH)3 could dissolve within 2 h at pH 9.5 and a portion of sediment P was dissolved concomitantly. Lowering pH to 7 caused 30–100% of the dissolved Al to precipitate again after 24 h. Re-precipitation of mobilized P varied from 50% to more than 100%. A test with untreated sediment showed the same proportionality which means that also indigenous Al(OH)3 can dissolve frequently in lakes with high pH water. Release rates of dissolved Al from intact sediment cores at the same three pH values was measured in three of the lakes, and showed increased Al release rates at pH 8.5 in one of the lakes and 9.5 in two of the lakes. Our study demonstrates a risk of dissolution of sediment Al(OH)3 to form aluminate in shallow lakes, where resuspension and high pH in the water occurs frequently. In the worst case dissolved Al may reach toxic levels in lakes treated by Al but also the concomitant release of P and the possible loss of dissolved Al to downstream ecosystems are negative effects that may occur already at more modest dissolution of Al(OH)3 and Al-bound P.

Chemical fractions and potential mobility of lead in soils irrigated by sewage in Pearl River Delta, South China

The chemical fractions, i.e., water soluble (WS), exchangeable (Ex), carbonate (Car), weakly organic (WO), Fe-Mn oxide (FMO), strongly organic (SO), residual (Res) fraction, of Pb in irrigated soils in South China were investigated by a modified Tessier sequential extraction technique. The results show that the chemical fraction of Pb in soil is mainly the Res fraction and followed by FMO fraction, and the WS, WO, FMO, and SO fractions in topsoils (0–10 cm) are higher than those in subsoils (30–40 cm). The sum of contents of WS and Ex fractions (S WE) in topsoils is significantly positively related with that in subsoils, indicating the strong mobility of Pb in WS and Ex fractions in soils, and the S WE in soils is higher than the German trigger value for the transfer path soil-plant, indicating the high bioavailability of Pb in soils of this area. Fortunately, S WE and the ratio of WS and Ex fractions (R WE) to the sum of all fractions generally decrease with the soil depth in soil profile and the R WE in soil profile is lower than 0.5%, indicating the low pollution risk for Pb in groundwater. In addition, soil particles, pH and Fe2O3 play an important role in the impact of mobility and chemical fractions of Pb in soils.

The distribution and chemical speciation of dissolved and particulate phosphorus in the Bering Sea and the Chukchi–Beaufort Seas

Water samples were collected from the Bering Sea and the Chukchi–Beaufort Seas during the 4th Chinese Arctic Research Expedition in summer 2010 to examine the abundance, spatial distribution and phase partitioning of phosphorus (P) between dissolved and particulate, inorganic and organic phases. Measurements of P species included dissolved inorganic P (DIP), dissolved organic P (DOP) and five particulate P species operationally defined by sequential extraction techniques. Inorganic P was generally the predominant form of both dissolved and particulate P, comprising on average up to 91±13% of the dissolved phase and 72±23% of the particulate phase in the study area. Concentrations of DIP in the water column of the Chukchi Sea and Bering Sea were considerably higher than those in the Beaufort Sea (>3μM vs. ∼1μM), showing a strong influence of North Pacific inflow waters. The percentage of DOP in the dissolved P pool was generally higher in surface waters than deeper waters, and higher in the Chukchi Sea than in the Bering Sea, consistent with their difference in primary productivity and reflecting sources of DOP from the surface waters. Within the particulate P pool, the labile P and ferric bound P were the two predominant species, especially in the upper water column (<1000m), while authigenic or CaCO3 bound P and detrital P were the two least abundant particulate P species. A positive correlation between labile particulate P and particulate organic carbon (POC) or particulate nitrogen (PN) was observed, where labile P concentrations decreased with increasing DIP concentrations and decreasing biological activity in the upper water column, indicating the contribution of labile particulate P from biological production. Labile P was an active component in regeneration of particulate P in the water column. The authigenic P was relatively abundant in deeper waters, especially in the Bering Sea, suggesting an active transformation between labile-P and authigenic P and a possible sink for P as authigenic particulate P in the deeper water column. In contrast to labile P, authigenic P, and organic P, the distributions of ferric-bound P and detrital P were mostly regulated by physicochemical processes, such as lateral transport and sediment resuspension. Therefore, different particulate P species could play a distinct role in biogeochemical cycling of P in the water column and understanding the detailed chemical and phase speciation of P should provide a better understanding of the dynamic cycling of P in the marine environment.

Chemical speciation and contamination assessment of Pb and V by sequential extraction in surface sediment off Nile Delta, Egypt

Environmental pollution caused by lead and vanadium is almost entirely due to industrial activities, such as the production of steel, pigments, photographic materials and insecticides.The concentration and chemical speciation of Pb and V were studied in surface sediments from 11 stations off Nile River Delta. Sequential extraction technique was applied to assess the four (exchangeable, acid-reducible, oxidizable-organic and residual) fractions in surface sediment, also to obtain an overall classification of lead and vanadium pollution in this area through its spatial distribution. This investigation was the first study on the basis of the chemical speciation of Pb and V in surface sediments off Nile Delta.The total concentrations of metals were ranged (22.8–41.3μgg−1) for Pb and (66.6–142.5μgg−1) for V. The chemical speciation in most sampling stations was in the order of Residual>acid-reducible>oxidizable-organic>exchangeable for Pb and in the order of Residual>oxidizable-organic>exchangeable>acid-reducible for V. The results showed that the Pb in surface sediments off Nile River Delta existed in the nonresistant fractions while vanadium existed in the resistant fractions. The degree of surface sediments contamination was determined for individual contamination factors (ICF) and global contamination factor (GCF). The result of ICF and GCF values showed that those stations located in the vicinity of municipal area (especially Lake Burullus outlet) had high potential risk to fauna and flora of study area. Risk assessment code (RAC) analysis indicated that although Pb presented a moderate overall risk to the aquatic environment, vanadium showed a low risk (RAC<10%) at six sites.

Sediment Pollution, Transport, and Abatement Measures in the City Canals of Delft, the Netherlands

This paper presents an overview of a long-term study on sediment pollution in the city canals of Delft, the Netherlands. This pollution was most evident for the inner city canal system, with copper, lead, zinc, and polycyclic aromatic hydrocarbons (PAHs) as main pollutants. Sediments of the outer city canals generally had a much better quality. Pollution levels, mutual correlations, and spatial variations were investigated for the various sediment parameters. Also, heavy metal binding forms onto Delft sediments were assessed with the help of sequential extraction techniques; results were found to be in line with expected preferential physicochemical binding processes. Input of sediments into the Delft inner city canals was shown to be largely driven by busy shipping traffic on the main canal surrounding the inner city. Mass balances for the inner city were used to quantify internal and external pollution sources; 65–85 % of the heavy metal pollution can be attributed to sources outside the Delft area. As shown by factor and cluster analyses, it is highly probable that these external sources derive from the river Rhine. A gradual improvement of the sediment quality has set in; it is expected that, due to further pollution abatement measures, this improvement will continue over the years to come. With respect to the ship-induced sediment input into the inner city canals, it was estimated that a reduction of ship velocities to <1.5 m/s will bring down the sediment input mentioned above to about 85 %.

An Investigative Study on the Chemical, Morphological and Mineralogical Alterations of Dry Disposed Fly Ash During Sequential Chemical Extraction

The hazardous elements associated with various physicochemical forms in coal fly ash are of environmental concern due to their leaching potential and subsequent contamination of surface and groundwater in the vicinity of the ash dump. Selective sequential extraction was performed on dry disposed fly ash samples from a coal-fired power station in Mpumalanga province, South Africa. The alteration of the chemical, morphological and mineralogical species of weathered fly ash during the selective sequential extraction was investigated using X-ray fluorescence (XRF), Nano-scan electron microscopy (NANOSEM) and X-ray powder diffraction (XRD). Insoluble residue from the water-soluble fraction is composed of amorphous alumino-silicate. The residues from exchangeable carbonate and Fe and Mn fractions consisted mostly of amorphous alumino-silicate spheres with a lesser quantity of iron-rich spheres. The iron-rich spheres are surrounded by amorphous alumino-silicate spheres. The leaching behavior of trace metals (such as Ce, Y, Nb, Rb, U, and Tl) in weathered dry disposed fly ash was considered to have a dependency relationship with the components of SiO 2 , CaO, MgO, P 2 O 5 , and amount of unburned carbon. The decrease in the quantities of calcite with successive extraction could be considered as a marker of progress of sequential extraction technique. At the same time, the increase in the quantities of quartz could be also considered as an indicator of progress of the sequential extraction scheme. Trace elements bound to exchangeable or carbonate fraction during sequential chemical extraction were found associated with calcite. The elemental concentrations, as determined by electron dispersive x-ray spectroscopy (EDS), were consistent with XRF and XRD data. Therefore, the chemical extractant used in this study proved efficient for extraction of inorganic metals associated with various physicochemical forms in weathered fly ash. Key words: Coal fly ash; Selective sequential extraction; Major components; Trace elements; Morphology; Mineralogical composition

Geochemical fractionation of 210Pb in oxic estuarine sediments of Coatzacoalcos River, Gulf of Mexico

210Pb activities were analyzed in surface sediments from the Coatzacoalcos River (Gulf of Mexico) to evaluate its distribution according to sediment grain size and in different geochemical compartments by using sequential extraction techniques. The geochemical fractionation experiments provided compatible results: by using the Tessier’s method [1] more than 90% of the 210Pb activity in the samples was found the residual fraction (primary and secondary minerals) and the remaining ( 80%), and the rest was found in the residual fraction. The grain size fractionation analyses showed that the 210Pb activities were mostly retained in the clay fraction, accounting up to 60–70% of the 210Pb total activity in the sediment sample and therefore, it is concluded that the separation of the clay fraction can be useful to improve the analysis of low 210Pb content sediments for dating purposes.

Heavy metals (Cr and Ni) distribution and fractionation in cropland soils from reclaimed tidal wetlands in Pearl River estuary, South China

Abstract Heavy metal contamination was compared for soils with different land use (cropland and wetland) in the reclaimed region of the Pearl River estuary. A sequential extraction technique was used to produce five chemical fractions (exchangeable (F1), carbonate (F2), Fe–Mn hydroxide (reducible) (F3), organic (F4) and residual (F5)) to study the effects of reclamation and tillage on the distribution and mobility of the heavy metals Cr and Ni. The results revealed that generally the contamination levels increased with a longer history of reclamation (100> 40> 30> 10 years) whilst an undisturbed reference wetland was least affected. The most substantial quantities of both Cr and Ni were observed in the residual fraction, which may be a consequence of the mixing effects of soil tillage and planting. With the exception of the 20-30 cm layers from the wetland and 10 year old cropland samples, the total concentration of Cr and Ni at all sites and all soil layers exceeded the moderately polluted level according to the SQGs of the US EPA.

Investigation of cesium adsorption on soil and sediment samples from Fukushima Prefecture by sequential extraction and EXAFS technique

Previous studies have shown that radiocesium (mainly 137 Cs) was retained at the very surface of soils in Fukushima Prefecture. Clay minerals and micas are assumed as the main sorbents for cesium (Cs) in Fukushima, but direct evidence is lacking for this hypothesis. In this study, radiocesium in the natural sample (soil and sediment) from Fukushima Prefecture was investigated through sequential extraction experiment (modified BCR method), which showed that more than 94% of 137 Cs was fixed in the residual phase. The results indicated that most of Cs occurred in the interlayer of phyllosilicate minerals. Furthermore, Cs LIII-edge extended X-ray absorption fine structure (EXAFS) showed that the Cs species adsorbed on the natural samples were very similar to those adsorbed on clay minerals and micas. This finding provided the direct evidence on the significant contribution of clay minerals or micas to Cs retention in soils from Fukushima Prefecture.

Temporal changes in the concentrations of zinc and cadmium in the sedimentary strata of Nozha Hydrodrome, Alexandria, Egypt

This study is concerned with the temporal changes in the levels of zinc and cadmium in the sediments of Nozha Hydrodrome during the past 100 years. Seven sediment core samples, covering the study area, were collected from the bottom of the Hydrodrome. A five-step sequential extraction technique was applied to determine the solid phase concentrations of zinc and cadmium. Zinc gives an idea of the quantities of sewage effluents, while cadmium provides an indication of the amounts of agricultural discharges. The vertical distribution curves show that the average total concentrations of zinc in the sediments increased at a rate of 2.5 μg g−1 y−1 from 1900 to 1950 and at 1.5 μg g−1 y−1 from 1950 to 1990. Since 1990 the zinc concentration in Nozha Hydrodrome sediments has been decreasing at 1.5 μg g−1 y−1. The average total cadmium concentration exhibits a different vertical distribution pattern: it increased at a rate of 0.42 μg g−1 y−1 from 1900 to 1950, after which it became constant from 1950 to 1970. Since 1970 it has been increasing at 0.53 μg g−1 y−1. The ongoing increase in cadmium concentrations in the sediments is due to the increase in agricultural discharges into the Hydrodrome, especially as significant amounts of phosphate fertilizers are used to nourish the soil around the Hydrodrome. The rise in cadmium concentrations since 1900 has been accompanied by a similar increase in zinc concentrations with time resulting from the discharge of untreated sewage into the Hydrodrome. In 1990 a sewerage system and sewage treatment plant came into operation, as a result of which discharges of domestic effluent into the Hydrodrome ceased. Since then the amount of zinc in sediments has been decreasing steadily.

The Speciation Transformation of Cd, Pb in Sludge Biology Leaching

This paper presents a systematic study of the biometric leaching sequencing batch experiment. The major process parameters include the inoculation amount of bacteria(5%) and substrate concentration(4g/L)(elemental sulfur). The chemical speciation transformation takes place in Biology leaching were measured by sequential extraction techniques. Through which before and after the leaching we can Analyze the filter mechanism and leaching ability. According to Cd, Pb content of each chemical speciation before and after the leaching, the release rules of different chemical speciation for each elements in every sampling period were calculated. This paper also analyzed the leaching ability of different chemical speciation in different leaching condition. The results indicated that,Cd drains out through the indirect mechanism, Pb drainings is mainly completes by direct machine-made and the indirect mechanism combined action.

Speciation of Chromium in Soil and Sludge in the Surrounding Tannery Region, Ranipet, Tamil Nadu

The distribution and mobility of chromium in the soils and sludge surrounding a tannery waste dumping area was investigated to evaluate its vertical and lateral movement of operational speciation which was determined in six steps to fractionate the material in the soil and sludge into (i) water soluble, (ii) exchangeable, (iii) carbonate bound, (iv) reducible, (v) oxidizable, and (vi) residual phases. The present study shows that about 63.7% of total chromium is mobilisable, and 36.3% of total chromium is nonbioavailable in soil, whereas about 30.2% of total chromium is mobilisable, and 69.8% of total chromium is non-bioavailable in sludge. In contaminated sites the concentration of chromium was found to be higher in the reducible phase in soils (31.3%) and oxidisable phases in sludge (56.3%) which act as the scavenger of chromium in polluted soils. These results also indicate that iron and manganese rich soil can hold chromium that will be bioavailable to plants and biota. Thus, results of this study can indicate the status of bioavailable of chromium in this area, using sequential extraction technique. So a suitable and proper management of handling tannery sludge in the said area will be urgently needed to the surrounding environment as well as ecosystems.

Speciative distribution and bioavailability of metals in agricultural soils receiving industrial wastewater

In order to assess the metal pollution status of agricultural lands of Mandi Bahauuddin receiving industrial wastewater, 35 top soil samples were investigated for the determination of selected metal levels, i.e., Fe, Cu, Cd, Cr, Ca, Ni, and Pb by flame atomic absorption spectroscopy under optimum analytical conditions. The distribution of these metals in different operationally defined chemical fractions was also determined by using the sequential extraction technique. The highest mean total concentration was found for Fe while the least one was observed for Pb. All the studied metals were found to be present at levels much enhanced than national and international standards. Moreover, most of the metals were distributed principally in residual fraction with the exception of Ni which was found to be associated mainly with oxidizable fraction. The significant correlations were observed between Fe-Mn oxide-bound and residual fractions and exchangeable and oxidizable fractions for most of the metals. The highest mobility was exhibited by Ni that evidenced its enhanced bioavailability in the soil. The multivariate statistical analyses in terms of principal component analysis (PCA) and cluster analysis (CA) revealed multiple sources for various geochemical fractions of different metals. CA also revealed that the nonresidual fractions of most of the metals were very closely associated while PCA presented a distinctive behavior of Ca in the soil. It was therefore suggested that in order to avoid the metal contamination arising from industrial wastewater, appropriate remediation strategies must be adopted.

Fractionation and potential risk of heavy metals in surface sediment of Nansi Lake, China

Fractionation of heavy metals in sediments can provide information on potential hazards of heavy metals. In this paper heavy metal pollution and release risk have been investigated by comparing total concentrations and fractionation of heavy metals (Cd, Cr, Cu, Fe, Pb, Mn and Zn) in Nansi Lake and the adjacent river sediments. Five chemical fractionations were extracted using Tessier’s sequential extraction technique. The percentage of carbonate and exchangeable fractions to the total content in sediment metals were measured. The data denoted that most sediment in Nansi Lake suffered certain pollution from heavy metals to some extent. The average concentrations of metals showed that the sediment was severely impacted by Cr and Zn, moderately impacted by Cd, Pb, Cu and Mn, and then slightly impacted by Fe. According to the risk assessment code, when carbonate and exchangeable fractions are 31–50% or more than 50%, the sedimentary metal presented a high or very high risk, respectively. The results indicated that Cd, Pb, Zn and Cr are potentially more mobile and at high or very high risk. In contrast, most Cu and Mn (65.38% and 53.85%) showed a medium risk, while iron was dominantly associated with residual fractions, therefore was immobile and most appeared no risk (61.54%) or low risk (34.62%).

Ecological risk assessment of heavy metals from the surficial sediments of a shallow coastal lagoon, Egypt

Sediment quality of Lake Maryout (one of the four Nile Delta shallow brackish water lakes on the south‐eastern coast of the Mediterranean Sea) is of concern as this lake is used for land reclamation and aquaculture and is an important fishing source. The magnitude and ecological relevance of metal pollution in Lake Maryout Main Basin was investigated by applying different sediment quality assessment approaches. The aim of this study was to estimate ecological risk of trace elements (Cd, Ni, Pb, Cr, Cu and Zn) in the surficial sediments (<63 µm fraction) of Lake Maryout. Heavily contaminated sediments were evaluated by the Sediment Quality Guideline (SQG) of the US Environmental Protection Agency. The degree of contamination (C d ) was estimated as very high for each site. Two sets of SQGs effect range‐low/effect range‐median values and threshold effect concentration (TEC) and probable effect concentration (PEC) values were used in this study. Sediments from each site were judged toxic when more of the PEC values exceeded EPA guidelines. Based on the geoaccumulation index (Igeo ) of target trace elements, the Main Basin of Lake Maryout has to be considered as extremely polluted with Cd (Igeo ≥ 5), strongly polluted with Zn (2≤ Igeo ≤ 3), moderately polluted with Cu (1≤ Igeo ≤ 2), unpolluted to moderately polluted with Cr and Pb (0≤ Igeo ≤ 1 for each) and unpolluted with Ni (Igeo ≤ 0). Lake Maryout sediments had heavy accumulations of Cd, which apparently come from drains that include industrial and raw domestic wastes. Therefore, a sequential extraction technique was applied to assess the five fractions (exchangeable, metals bound to carbonate, acid‐reducible, oxidizable‐organic and residual) of Cd in surface sediments. The Cd concentration in most sampling stations was dominated by the non‐resistant fraction (anthropogenic). The result showed that those stations located in the vicinity of municipal and mixed waste drains posed a high potential risk to fauna and flora of Maryout Lake.

Chemical Fractionation of Trace Metals in Sewage Water – Irrigated Soils

The bioavailability of trace metals, their biological uptake and ecotoxiccological effect on soil biota can be better understood in terms of their chemical fractionation. The present study examined the mobility and availability of Cd, Cu, Ni, Pb and Zn in sewage water – irrigated soils using sequential extraction technique as a basis for predicting metal uptake by plants. The residual fraction was the most abundant pool for all the five metals examined. A significant amount (2.7 – 70.2%) of all the five metals was also present in the potentially available fraction: - nonresidual fraction. The result further indicated that the contamination of Cd and Ni in these soils was not as severe as Pb, Cu and Zn. Assuming that mobility and bioavailability of these metals are related to their liability and geochemical forms, and that they decrease in the order of extraction sequence. The apparent mobility and potential bioavailability for these five metals in the soils were: - Pb> Zn> Cu> Ni> Cd.

Application of chemical fractionation and X-ray powder diffraction to study phosphorus speciation in sediments from Lake Hongfeng, China

Based on the techniques of sequential extraction and X-ray powder diffraction (XRD), the distribution characteristics of phosphorus speciation were investigated in 13 sediment samples from Lake Hongfeng, an important drinking water source for Guiyang with a typical karstic limestone environment. The total phosphorus (TP) concentrations in the sediments ranged from 973.36 to 2334.18 mg/kg with a mean concentration of 1635.87 mg/kg (dry weight), and it was evident that the phosphorus level in the sediments was high compared with other eutrophic lakes such as Lake Chaohu and Lake Xihu. The results of the two methods, sequential extraction and XRD, demonstrated the presence of different phosphorus species in the lake sediments. Being compatible with local geophysical characteristics, the results of sequential extraction techniques indicate that the average percentages of dissolved phosphorus (DP), aluminum-bound phosphorus (Al-P), iron-bound phosphorus (Fe-P), calcium-bound phosphorus (Ca-P) and organic phosphorus (OP) in the sediments were 0.40%, 7.06%, 5.07%, 45.48% and 38.49%, respectively. Notably, the concentrations of inorganic phosphorus (IP) were higher than those of OP, and the IP consisted primarily of Ca-P. The high concentrations of Ca-P may temporarily control the release of phosphorus from the sediments because it is a relatively stable, inert and non-bioavailable phosphorus fraction. The results of XRD analysis indicated that, among phosphorus species, AlPO4 was found in all sediment samples at relatively high concentrations. Moreover, the TP concentrations in the sediments were high; thus the release potential and bioavailability of phosphorus in the sediments was important. Further statistical analyses of the results revealed significant correlations between phosphorus species in the sediments with two extractable principal components and four selectable cluster levels allowing interpretation of possible origins of phosphorus loading and transformation mechanisms of phosphorus species. Furthermore, available remediation measures were briefly assessed for the lake while considering its distinct environmental features.