Physical fractionation of trace and rare earth elements in the sediments of Lake Nasser

The distribution of major, trace and rare earth elements in bulk, different particle sized and strongly magnetic fractions of Lake Nasser sediments has been investigated. The elements were determined using neutron activation analysis. Statistical data processing indicates good correlation between Th, La and Ce, suggesting that accessory minerals such as monazite may play a role in controlling rare earth elements (REE) in the lake sediments. The highly significant relationship between Al and light-REE accounts for the capability of clay minerals to host these elements. In addition, principle components analysis reflects that there are only four factors which could explain about 90% of the total variance in the lake sediments. The results show also that Al, Th and REE have low contents in the sediment magnetic fraction relative to the corresponding values in the bulk sediments, whereas Fe, Mn, Ti, Co, Cr, Hf, V and Zn have higher concentrations in the same fraction than the corresponding values in the bulk sediments. This may be attributed to their incorporation in Fe-Mn minerals.     

The geochemistry of uranium in pore waters from lake sediments

The concentration of pore water uranium in six sediments from oligotrophic, mesotrophic, acidotrophic and dystrophic lakes was measured by inductively coupled plasma-mass spectrometry. Profiles of pore water U can be divided into two groups such as low (17±7 ng/l) and high concentration (69±30 ng/l). These values were 1–2 orders of magnitude higher than that of lake waters (6±4 ng/l) due to the release of U from the sediments by decomposition of organic materials. Variations in pore water U concentrations seem to relate to the differences in pore water pH, the association forms, and their contents of U in the lake sediments.     

Study of phosphorus distribution in coastal surface sediment by sequential extraction procedure (NE Mediterranean Sea, Antalya-Turkey)

The paper presents the results of the distribution of phosphorus (P) bioavailability (total P, organic and inorganic P) in marine surface sediments collected from four coasts that are under different anthropogenic pressures of NE Mediterranean Sea (Alanya, Serik, Kemer, Finike — Antalya, Turkey) in May, 2009. Speciation of inorganic phosphorus (IP) was carried out using a method on sequential extractions, with each releasing four forms of IP — loosely bound P, phosphorus bound to aluminum (P-Al), phosphorus bound to iron (P-Fe), and phosphorus bound to calcium (P-Ca) and determined by the inductively coupled plasma-optical emission spectrometer (ICP-OES). The total P contents ranged from 152.18 to 275.12 mg/kg. It was found that more than 96% of the total P is IP. Among the four forms of IP, IP distribution ranges were 1.20-3.59% for loosely bound P, 2.38-4.74% for P-Fe, 4.43-8.55% for P-Al, and 84.36-91.99% for P-Ca. The region of Alanya was characterized by the highest total P concentration in the surface sediment than Serik, Kemer, Finike sediments. For all the marine surface sediment samples, the rank order of inorganic P-fractions was Ca-P > Al-P > Fe-P > loosely bound P.     

Geochemical association of137Cs and239,240Pu in the oligotrophic and mesotrophic lake sediments

Geochemical association of¹³⁷Cs and^239,240Pu in the surface sediments from two oligotrophic and mesotrophic lakes in Japan was studied by sequential chemical extractions. The fractions separated were exchangeable and bound to carbonate, bound to oxides, bound to organic mattersulfides, and residual. The¹³⁷Cs and^239,240Pu were mainly associated with the organic matter-sulfides and residual fractions but exhibited the different vertical profiles at both lakes. The differences in association patterns between the lakes may be controlled by transport of these nuclides by organic settling particles to the bottom sediments and decomposition of the organics in the sediments.     

Lanthanide–actinide separation by bis-2-ethylhexylphosphoric acid from citric acid–nitric acid medium

Phosphate rock (Pho-ore) is the starting raw material used in manufacturing of most phosphate products. This material contains phosphorous, natural uranium, thorium potassium radionuclide and other trace elements. Single super phosphate powder (SSPho-P), single super phosphate granules (SSPho-G), and triple super phosphate (TSPho) are the common phosphate products produced along with phosphogypsym (CaSO₄) as a waste product. Since these materials are industrially manufactured by the reaction of the phosphate ore with phosphoric and sulphuric acids, these products and the waste product are extremely acidic. Pho-ore, SSPho-P, SSPho-G, TSPho and CaSO₄ samples were used in our study. Chemical analyses showed that these phosphate samples contain phosphorous, iron, aluminum ions and traces of uranium ions. Accumulation of the fertilizers on soils usually transfers some of these ions from the fertilizer materials to the soil/water interfaces. The migration of uranium U(VI), P, Al and Fe in subsurface soils was found to be strongly influenced by the sorption/desorption reaction at the solid/water interfaces. Thus, dissolution of these ions in soil/water phases is very important. Speciation of U(VI), P, Al and Fe in soil/water phases were calculated using a geochemical code (MINTEQA2). This study was conducted to determine sorption properties and the surface electrical properties of these ions at the soil samples.     

Assessing spatial distribution,sources, and potential ecological risk of heavy metals in surface sediments of the Nansi Lake,Eastern China

The study is conducted to investigate the spatial distribution, sources and ecological risk of seven heavy metals in surface sediments of Nansi Lake, Eastern China. A total of 29 samples were collected in surface sediments of Nansi Lake, and were analyzed for three nutrients (TN, TOC and TP), two major metals (Al and Fe), as well as seven trace metals (As, Cd, Cr, Cu, Hg, Pb and Zn). The mean concentrations of As, Cd, Cr, Cu, Hg, Pb, Zn, Fe and Al were 14.41, 0.22, 71.10, 30.1, 0.048, 29.14, 90.2, 30,816 and 70,653 mg kg^?1, respectively, and the mean contents of these metals were higher than the background values with the exception of Cu and Fe. The spatial distribution indicated that the contents of all seven heavy metals were characterized by relatively higher contents in the upper lake than the lower lake. The hotspots with high values of As, Cd and Hg were associated with the river mouths, and the hotspots of Pb were mainly located around the dam in the central part, while no significant associations were displayed between spatial distribution of Cr, Cu, Zn and the river mouths. The mean enrichment factor (EF) values of As, Cd, Hg and Pb were 2.03, 2.93, 3.21 and 2.18, respectively, showing their moderate enrichment, while Cr, Cu and Zn with mean EF values of 1.19, 0.89 and 1.01 were deficiency to minimal enrichment. Multivariate and geostatistical analyses suggested that PC1 controlled by Cr, Cu and Zn was a lithogenic component, and come from parent rocks leaching. PC2 including Cd and partially Hg represented the factor from industrial wastewater discharge. PC3 showed elevated loadings of As and partially Cd, and could be attributed to the agricultural practices. While PC4 including Pb and partially Hg, was dominated by coal combustion. The results of potential ecological risk suggested that sediment environment of Nansi Lake suffered from high ecological risk.     

Kinetics and energetics of phosphate sorption in a multi-component Al(III)-Fe(III) hydr(oxide) sorbent system

Multi-component Al-Fe hydr(oxides) are ubiquituous in soil and aquatic environments, where they exhibit biogeochemical controls on nutrients and contaminants. Although, sorption on single-component Al and Fe hydr(oxides) have been extensively studied, limited studies have been done on their multi-component counterparts. In this study, effects of Al/Fe content on the kinetics and energetics of phosphate sorption in a poorly-crystalline co-precipitated mixed Al-Fe hydr(oxide) system were investigated using a combination of traditional batch techniques and flow adsorption calorimetry. Differences in Al/Fe content was found to influence the structural development and anion exchange capacity of the hydr(oxides) and subsequently their phosphate sorption characteristics. Higher structural development decreased phosphate sorption, while higher AEC was associated with increased phosphate sorption, initial sorption rate, and smaller losses in sorption with increasing pH. Results from flow adsorption calorimetry indicated that at pH 4.8 phosphate sorption: (i) occurred irreversibly on anion exchange sites, with a loss of 1.9 moles of AEC per mole of phosphate sorbed, and (ii) was exothermic, with molar heats of adsorption between -25 and -39 kJmol(-1). Molar heats of adsorption were ten times that for anion exchange and independent of hydr(oxide) composition with the amount of energy evolved being directly proportional to the quantity of phosphate sorbed.     

Removal of phosphate from aqueous solution by zeolite synthesized from fly ash

Fifteen Chinese fly ashes were converted hydrothermally into zeolites, and phosphate immobilization capacity (PIC) of the synthesized zeolites and the corresponding raw fly ashes were determined using an initial phosphate concentration of 1000 mg/L. Results showed that there was a remarkable increase in PIC (from 1.2 to 7.6 times) following the synthesis process. Fractionation of immobilized phosphorus indicated that Fe+Al-P increased most significantly and consistently among all the phosphorus fractions following the conversion of fly ash to zeolite. The PIC and Ca+Mg-P were closely related to Ca content (with r values of 0.9683 and 0.9651, respectively) rather than Mg content (with r values of 0.3920 and 0.3212, respectively). The r values of PIC and Fe+Al-P with Fe content (with r values of 0.4686 and 0.6385, respectively) were higher than those with Al content (with r values of -0.7857 and -0.3770, respectively). Although calcium and iron components were mainly involved in phosphate immobilization, there was no significant change of Ca and Fe content following the conversion of fly ash to zeolite. Increase in dissociated Fe(2)O(3) and specific surface area probably accounted for the enhancement in PIC of synthesized zeolites compared with corresponding fly ashes. The PIC value of zeolites showed a significant correlation with dissociated Fe(2)O(3) (r=0.6186). The specific surface area increased 26.0-89.4 times as a result of the conversion of fly ash to zeolite. The maximum removal of phosphate occurred within different pH ranges for zeolites which were synthesized from high, medium and low calcium fly ashes and this behavior was explained by the reaction of phosphate with calcium and iron components.     

Effects of freeze-drying on partitioning patterns of major elements and trace metals in lake sediments

The effect of freeze-drying on elemental partitioning pattern in four lake sediments was evaluated using the sequential extraction method developed under the auspices of Community Bureau of Reference (BCR) of the Commission of European Communities. Redox-sensitive elements like iron, manganese, phosphorus, and sulfur were analyzed simultaneously with several trace metals. This allows a qualitative determination of which trace metal-scavenging phases commonly found in freshwater sediments that are most susceptible to freeze-drying.The comparison of a surface layer and a deeper more reduced layer collected from four sediment cores ranging from sub-oxic to anoxic condition indicate the changes in partitioning pattern due to freeze-drying. Two of the lakes exhibiting clearly reduced environments are most affected by freeze-drying in terms of change in partitioning patterns. However, this effect is element specific and varies with sediment depth along the redox gradient. Elements commonly associated with a sulfide phase (S, Fe, Cu, Zn, and Pb) and extracted in BCR step 3 are the most affected elements, but at the same time also dependent on the organic matter content in the sediment. Si and Al that are often considered as conservative elements show a shift from step 3 to step 2, and it is interpreted as a release of Si and Al from organic matter and the subsequent formation of oxides during freeze-drying. Calcium and manganese, elements that are often associated with a carbonate phase, do not seem to be severely affected by this kind of treatment. Carbonate-associated iron (operationally defined), however does show a clear tendency to oxidize during the freeze-drying process. In fact, the shift in iron (carbonate to oxide fraction) corresponds to 3-4% (w/w) of the total sediment in some cases. Surprisingly, a significant fraction of iron originally extracted in step 1 (as “carbonate”) seems to be immobilized during freeze-drying.These results clearly show that freeze-drying does not preserve the speciation pattern of major elements, trace metals, phosphorus, and sulfur in anoxic lake sediment core sections during storage prior to BCR sequential extraction procedures.     

Trophic status of fresh-water lakes in China

In the article the trophic status of thirty one fresh-water lakes of China was described. Four lakes are characterized as mesotrophic, seventeen lakes have eutrotrophic status, and ten lakes are hypertrophic. Critical phosphorus loading for five biggest fresh-water lakes was calculated. The relationship between average and maximal depth of 141 lakes was revealed.     

大亚湾表层沉积物中生源要素的季节分布及污染评价

2006年7月至2007年11月采集了大亚湾10个采样点春、夏、秋和冬4季表层沉积物样品,分析了沉积物中的生物硅(BSi)、有机碳(TOC)、总氮(TN)和总磷(TP)含量。结果表明:大亚湾生源要素含量与国内外港湾相比属于中等水平;春季BSi、TP的平均含量分别为1.09%、0.043%;夏季BSi、TOC、TN、TP的平均含量分别为1.21%、1.05%、0.37%、0.043%;秋季BSi、TP的平均含量分别为0.99%、0.038%;冬季BSi、TOC、TN、TP的平均含量分别为1.09%、0.84%、0.11%、0.039%。根据TN/TP和TOC/TN比值判断,大亚湾沉积物为磷限制;夏季TOC主要来源于水生有机碳,冬季为混合来源。夏季表层沉积物中BSi、TOC、TN和TP的平均含量均高于其他季节;其中夏季各站位TN的含量较冬季要高,反映了夏季较高的硅藻生产力以及较丰富的地表径流。大亚湾大部分采样点TOC和TN的污染基本属于Ⅱ类,TP属于Ⅰ类,可能对底栖生物群落具有一定毒害作用。     

Characterization of phosphate solubilizing bacteria in sediments from a shallow eutrophic lake and a wetland: isolation, molecular identification and phosphorus release ability determination

The transformation of phosphorus (P) is a major factor of lake eutrophication, and phosphate releasing bacteria play an important role in the release process. Experiments were conducted to investigate P content and characterize phosphate solubilizing bacterial composition at the molecular level in a shallow eutrophic lake and a wetland. Results showed that P concentrations were relatively high and derived from agricultural runoff and domestic or industrial pollution. Enumeration and molecular identification of these strains indicated that these bacterial groups were abundant in the ecosystem and various kinds of bacteria participated in the phosphorus release process. Twelve phosphate solubilizing bacteria, including eight organic P-solubilizing bacteria (OPBs) and four inorganic P-solubilizing bacteria (IPBs), which belonged to three different families, were isolated and identified. Cupriavidus basilensis was found for the first time to have the ability to mineralize organic P (OP). Laboratory tests on P release ability revealed that IPBs were more effective at releasing P than OPBs. The most efficient IPB strain could accumulate over 170 mg·L-1 orthophosphate, while the equivalent OPB strain only liberated less than 4 mg·L-1 orthophosphate in liquid culture. The results obtained from this investigation should help clarify the roles of microorganisms in aquatic systems and the mechanisms of eutrophication.     

南四湖各生态功能湖区垂向沉积物的磷吸附特征

研究了南四湖各生态功能湖区(养殖区、禁渔区、航道及湖滨带)垂向不同深度沉积物对磷的吸附动力学及等温吸附曲线,并分析了沉积物各形态磷与磷吸附特征参数的相关关系.研究结果表明:①各层沉积物对磷的吸附在10h内基本达到平衡,最大吸附量Qmax随着沉积深度的增加而增大;②随着沉积深度的增加,吸附-解吸平衡浓度Cepc和本底吸附态磷ωNAP含量均逐渐减小,吸附效率m逐渐增大;③吸附-解吸平衡浓度Cepc与Ex-P、Fe-P含量显著正相关,最大吸附量Qmax与Ex-P、org-P和TP含量均呈显著负相关关系,本底吸附态磷ωNAP与Ex-P、De-P含量呈显著正相关关系,吸附效率m仅与org-P含量呈显著正相关关系.     

Simultaneous removal of ammonium and phosphate by zeolite synthesized from fly ash as influenced by salt treatment

To develop an effective technique for enhancing the removal efficiency of ammonium and phosphate at low concentrations without losing potential removal capacity, Na-ZFA (zeolite synthesized from fly ash) was converted into Ca-, Mg-, Al-, and Fe-ZFA by salt treatment and the simultaneous removal of ammonium and phosphate by ZFA saturated with different cations was investigated. It was shown that Al3+-ZFA had the highest removal efficiencies (80-98%) for ammonium, followed by Mg2+ (43-58%), Ca2+ (40-54%), Na+ (<20%), and Fe3+ (<1%). Both alkaline pH values (in the cases of Na+, Ca2+, Mg2+) and acidic pH value (in the case of Fe3+) inhibited the sequestration of ammonium. At low initial phosphate concentrations, the efficiency of phosphate removal by Al3+- and Fe3+-ZFA approached 100%, followed by Ca2+ (60-85%), Na+ (<25%), and Mg2+ (<5%). The difference in phosphate removal efficiency was explained by the adsorption mechanisms. It was concluded that ZFA could be used in simultaneous removal of NH4+ and phosphate at low concentrations with presaturation by an appropriate cation such as Al3+ through salt treatment.     

Shortened screening method for phosphorus fractionation in sediments: A complementary approach to the standards, measurements and testing harmonised protocol

The SMT protocol, a sediment phosphorus fractionation method harmonised and validated in the frame of the standards, measurements and testing (SMT) programme (European Commission), establishes five fractions of phosphorus according to their extractability. The determination of phosphate extracted is carried out spectrophotometrically. This protocol has been applied to 11 sediments of different origin and characteristics and the phosphorus extracted in each fraction was determined not only by UV-Vis spectrophotometry, but also by inductively coupled plasma-atomic emission spectrometry. The use of these two determination techniques allowed the differentiation between phosphorus that was present in the extracts as soluble reactive phosphorus and as total phosphorus. From the comparison of data obtained with both determination techniques a shortened screening method, for a quick evaluation of the magnitude and importance of the fractions given by the SMT protocol, is proposed and validated using two certified reference materials.     

Geochemical characterisation of Antarctic soils and lacustrine sediments from Terra Nova Bay

In Terra Nova Bay region (northern Victoria Land, Antarctica), the interactions among soil, meltwater and lakes are poorly understood with regard to the physicochemical transformations that occur when solid materials are exchanged among them. In order to ascertain the natural dynamics of several elements, namely Al, As, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Ti and Zn, as well as the perturbations by human activities and/or global contamination, soils and sediments from four catchments (Tarn Flat, Edmonson Point, Inexpressible Island and Northern Foothills) were studied.To accomplish the above mentioned objectives, the particle-size distribution and mineralogical composition, as well as the total C, H and N contents and the total concentrations of the investigated elements were determined. Finally in order to assess metal mobility, the modified BCR three-step sequential extraction procedure was applied to the samples and the partitioning of five metals, namely Cr, Fe, Mn, Pb and Zn, into different fractions was determined.Lithology and topography are the main factors that differentiate the physicochemical characteristics of the soils and sediments investigated. The lacustrine sediments and the soils sampled around the lakes showed a similar mineralogical and chemical composition, as evidence that rock- and soil-weathering processes occur primarily during the warm summer periods, when the lakes are partially ice-free. Nevertheless the presence of chlorite in these systems indicated that chemical weathering has taken place even in these extreme conditions. In general, the geochemical composition of soils and sediments in this Antarctic area seems to be influenced mainly by the nature of the bedrock and by the input of sea-spray, and, to a lesser degree, by mechanical and chemical weathering as well as by biological processes; no evidence of a local or global anthropogenic contamination was found.     

Water quality of two glacial alpine Italian lakes

The purpose of this study was to characterize, in a period of one year, two glacial lakes, Alice and Meugliano, located in an alpine reservoir on the basis of physical and chemical features. The two lakes show two periods of mixing: one in the spring and one in the autumn, so can be classified as dimictic lakes. They are characterized by pH, alkalinity, low conductivity and and quite dilute ionic concentrations. With regard to nutrients, most nitrogen occurred in the nitric form in the superficial layers. During the period of thermal stratification, in the anoxic layer NO3- decreases and NH4+ increases, confirming the activity of the anaerobic denitrificant bacteria. Total and soluble phosphorus levels show homogeneity during the cold period at different depths, while with stratification concentrations increase in the hypolimnium and metalimnium. In both lakes there is an inverse correlation between transparency and chlorophyll a. To evaluate the trophic state the conventional criteria of Nurnberg 2 and four lake trophic indices (TSIs) are used. Both evaluations suggest that the two lakes are eutrophic, with worse conditions in Alice. Deviations of the trophic states, based on the relation between TSIs, indicate that factors other than phosphorous limit the algal biomass, and that non-algal particles influence light attenuation     

Fluoride sorption and associated aluminum release in variable charge soils

Fluoride sorption and related aluminum (Al) release are evaluated in two iron-oxide-rich soils as a function of soil depth, composition, and physical-chemical properties and potential mechanisms of fluoride-surface interaction are suggested. Measured Al concentrations at equilibrium fluoride sorption, reflective of the net balance between Al dissolution and sequestration of the released Al by the solid phase, suggest net fluoride-assisted dissolution of Al-bearing amorphous and crystalline soil minerals. Strikingly, soils of similar depth and horizonation from the same soil order but of distinct soil series exhibited markedly different susceptibility to Al loss in the presence of fluoride, possibly a combined result of differences in the mechanism of fluoride sorption, soil mineralogy, reactivity of the surficial Al and Fe, and soil solution chemistry. Fluoride sorption is strongly correlated with soil Al and Fe present as high-surface-area amorphous and crystalline oxide phases. Fluoride complexation to surficial Al and Fe ions via ligand exchange with surficial OH groups and water molecules appears to be the dominant sorption mechanism. At high dissolved fluoride concentrations (>7 mM), other mechanisms of fluoride retention including adsorption of AlF solution complexes, entrapment in the interparticle pore fluid, and precipitation into solution and/or onto the soil surface are also likely.     

The use of silica-immobilized brown alga (Pilayella littoralis) for metal preconcentration and determination by inductively coupled plasma optical emission spectrometry

The brown alga Pilayella littoralis was used as a new biosorbent in an on-line metal preconcentration procedure in a flow-injection system. Al, Co, Cu and Fe were determined in lake water samples by inductively coupled plasma optical emission spectrometry (ICP-OES) after preconcentration in a silica-immobilized alga column. Like other algae, P. littoralis exhibited strong affinity for these metals proving to be an effective accumulation medium. Metals were bound at pH 5.5 and were displaced at pH<2 with diluted HCl. The enrichment factors for Cu^II, Fe^III, Al^III and Co^II were 13, 7, 16 and 11, respectively. Metal sorption efficiency ranged from 86 to 90%. The method accuracy was assessed by using drinking water certified reference material and graphite furnace atomic absorption spectrometry (GFAAS) as a comparison technique. The column procedure allowed a less time consuming, easy regeneration of the biomaterial and rigidity of the alga provided by its immobilization on silica gel.     

Fractionation of elements in sediment samples collected in rivers and harbors at Lake Balaton and its catchment area

A monitoring system has been developed to characterize the water quality of Lake Balaton. Sediment samples were collected in rivers and harbors around the lake and its catchment area. A modified four-step sequential leaching procedure was applied for determination of the distribution of elements. The fractions were: (1) exchangeable/bound to carbonate; (2) bound to Fe/Mn oxide; (3) bound to organic matter/sulfides; and (4) acid-soluble residue. Samples were taken in three seasons and the average concentration of the elements was calculated. Concentrations of elements were mostly well below the Hungarian standards set for soils and geochemical background values. Most of the elements were found in the acid-soluble residue and bound to organic matter/sulfide fractions, characterizing stable compounds in sediments. There was a difference on the elemental composition of sediments collected at rivers in the catchment area and harbors with relatively small boat traffic. Depending upon the nature of element and local pollution sources the concentration of Pb and Cu ions was found higher in sediments taken at harbors than that of small rivers. Generally, it can be stated that elemental concentration of sediments inside of the lake is smaller than at the catchment area, so the pollution from emission sources has not reached the lake yet.