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1.
Screening out plants that are hyper-tolerant to certain heavy metals plays a fundamental role in remediation of mine tailing. In this study, nine dominant plant species growing on lead–zinc mine tailing and their corresponding non-mining ecotypes were investigated for their potential phytostabilization of lead. Lead concentration in roots of these plants was higher than in shoots, and the highest concentrations of lead were found in Athyrium wardii: 15542 and 10720 mg kg−1 in the early growth stage (May) and vigorous growth stage (August) respectively, which were 426 and 455 times higher than those of the non-mining ecotypes. Because of poor lead translocation ability, lead accumulation in roots reached as high as 42 mg per plant. Available lead in the rhizosphere soils of A. wardii was 310 mg kg−1, which was 17 times higher than that of the non-rhizosphere soil. Lead concentrations of roots for the nine mining ecotypes were positively correlated with available lead in the rhizosphere soils, whereas a negative correlation was observed in the non-mining ecotypes. These results suggest that A. wardii was the most promising candidate among the tested species for lead accumulation in roots, and it could be used for phytostabilization in lead polluted soils.  相似文献   

2.
To assess the competitive sorption and desorption of cadmium (Cd) and lead (Pb), batch equilibrium experiments were performed using single- and binary-metal solutions in surface samples of three paddy soils from eastern China. Sorption isotherms were well fitted with one-metal and competitive Langmuir equation for single- and binary-metal system, respectively. The distribution coefficient (K d) values were K d single (Pb) > K d binary (Pb) > K d single (Cd) > K d binary (Cd), indicating that Pb was stronger sorbed by these soils than Cd in binary metal system. Soils with high pH and clay content had the greatest sorption capacity as estimated by the maximum sorption parameter (Q). The co-existence of both metals reduces their tendency of sorption, whereas Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter (b) in binary sorption system was greater than that in single sorption system for all soils (b < b 1), indicating that competition for sorption sites promote the retention of both metals into more specific sorption sites. Sorption of Cd and Pb decreased soil pH by 1.61 U for YRS, 1.39 U for PCS, and 0.91 U for SLS. The decreases of pH in binary metal system were greater than in single-metal system for three soils. Cadmium and Pb desorption increased with increasing Cd and Pb sorption saturation for all soils; however, Cd desorption ratio in binary metal system (d Cd*) was much greater than Pb (d Pb*), indicating that under the competitive sorption conditions, the sorbed Cd was more readily desorbed from the soils than the sorbed Pb.  相似文献   

3.
Cadmium (Cd) pollution highly threats to rice consumption for humans. This study aims to investigate the variation of Cd uptake and translocation among rice lines and to screen cadmium-safe cultivars (CSCs). Total of 146 rice lines were grown in artificially Cd pollution hydroponics within 30 day followed by a pot culture in which 17 rice lines were planted and treated with different Cd levels until maturity. The results showed that Cd tolerance and Cd accumulation significantly (p < 0.05) varied among 146 rice lines in the hydroponics experiment as well as among the 17 rice lines in the followed pot culture. Cd contents of brown rice significantly correlated with Cd accumulations in plant and their translocation from vegetative organs to edible parts, implying that extremely attention should paid to Cd translocation and its influence factors for CSCs selection. IRBN95-90 and D26B of maintainer lines and Lu5278-I332, Lu17-T21712, Lu17-I2R60 of restorer lines were detected to be potential CSCs under 2 and 10 mg kg?1 Cd level, which confirmed the feasibility of selection of CSCs from rice lines. Therefore, the study confirmed the variations of Cd uptake and translocation among rice lines and a combinatorial and recursive selection process is feasible and affordable to screen CSCs to reduce Cd risk for rice consumption.  相似文献   

4.
Heavy metals are governed by parent material of soils and influenced by the soil physicochemical properties and soil and crop management practices. This paper evaluates total heavy metal concentrations in rainfed soils under diverse management practices of tropical India. Vertisols (clayey soils with high shrink/swell capacity) had the highest concentrations of heavy metals. However, chromium (Cr) content was above the threshold value in Aridisol [calcium carbonate (CaCO3)]-containing soils of the arid environments with subsurface horizon development. Concentration increased at lower depths (>30 cm). Basaltic soils showed higher concentrations of nickel (Ni), copper (Cu) and manganese (Mn). Cadmium (Cd), cobalt (Co), Cu and Mn concentrations were higher in soils cultivated to cotton, whereas Cr concentration was above the threshold level of 110 mg kg?1 in food crop cultivated soils. As the specific soil surface is closely related to clay content and clay type, soil’s ability to retain heavy metals is more closely tied to the specific surface than to the soil cation exchange capacity. Higher positive correlations were found between heavy metal concentrations and clay content [Cd(r = 0.85; p ≤ 0.01); Co (r = 0.88; p ≤ 0.05); Ni (r = 0.87; p ≤ 0.01); Co (r = 0.81; p ≤ 0.05); Zn (r = 0.49; p ≤ 0.01); Cr (r = 0.80; p ≤ 0.05); Mn (r = 0.79; p ≤ 0.01)]. The amounts of nitrogen–phosphorus–potassium applied showed a positive correlation with Co and Ni (r = 0.62; p ≤ 0.05). As several soils used for growing food crops are high in Ni, Cr and Mn, the flow of these metals in soil–plant–livestock/human chain needs further attention.  相似文献   

5.
This research presents a detailed study which was performed to infer the quantity of metal (Cd, Cr, Pb, Zn, Cu and Fe) contents in sediments of Daye Lake, Central China. The geo-accumulation (I geo) and potential ecological risk (PER) of these metals were assessed. The results reveal that: (1) the mean value of I geo ranked an order of Fe (class 6) > Cd (class 5) > Pb (class 3) > Zn (class 2) > Cr (Class 1) > Cu (Class 0); (2) Potential ecological risk (PER) values calculated for all these metals at different sampled points in Daye Lake exceeded the value of very high risk. Multivariate statistical analyses were carried out to determine the relationship between these six metals and to identify the possible pollution sources, with the results suggesting that the metal content in the sediments has three patterns: the first pattern includes Pb, Cd and Cr which were mainly present due to discharged water by smelting industries; second pattern contains Zn and Cu which mainly originated from the waste residue of the copper mining industry; the third pattern is Fe which is mainly related to mine tailing leaches. This study indicates very high metal content levels in the sediments, which may have adverse risks (average PER = 7,771.62) for the lake’s ecosystem and human beings associated with Daye Lake.  相似文献   

6.
Pollution by heavy metals presents an environmental concern, and their toxicity threats soil, water, animals and human health. Phytoremediation can be used as a solution to remediate contaminated soils. The aim of this study was to identify native plants collected from tailings: material of Pb–Zn mine sites of Fedj Lahdoum and Jebel Ressas (two abandoned mines located, respectively, in the northwest of Tunisia and in the south of Tunis City). The tolerance of plant to heavy metals (lead, zinc and cadmium) is evaluated. Soil samples were collected and analyzed for Pb, Zn and Cd concentration. The total soil Pb, Zn and Cd are, respectively, reached 6132 mg kg?1, 11,052 mg kg?1 and it doesn’t exceed 479 mg kg?1 for Cd. The highest content of Zn in plants was detected in shoots of Rumex bucephalophorus (1048 mg kg?1), and the highest Pb concentration was detected in roots of Chrysopogon zizanioides (381 mg kg?1), while for Cd Silene colorata it accumulated the highest content in roots (51 mg kg?1). From all plants, only 12 have a translocation factor for Pb which is higher than one. Among all plants, only 17 have a translocation factor that is higher than one for Zn, while for Cd only 13 plants indicate TF > 1. As for the biological absorption coefficient, all samples indicate a rate which is lower than one. These plants can be primarily hyper accumulators and useful in remediation of lead- and zinc-contaminated soils after further biochemistry researches in mechanism of accumulation and translocation of heavy metals in plants.  相似文献   

7.
The goal of this study was to evaluate the soil properties and their modifications within the rhizosphere of spontaneous vegetation as key factors to assess the phytomanagement of a salt marsh polluted by mining wastes. A field survey was performed based on a plot sampling design. The results provided by the analyses of rhizospheric soil (pH, electrical conductivity (EC), organic carbon, total nitrogen, etc.) and metal(loid)s’ phytoavailability (assessed by EDTA) were discussed and related to plant metal uptake. The averages of pH and EC values of the bulk soil and rhizospheric samples were in the range of neutral to slightly alkaline (pH 7–8) to saline (>2 dS m?1), respectively. Heavy metal and As concentrations (e.g. ~600 mg kg?1 As, ~50 mg kg?1 Cd, ~11,000 mg kg?1 Pb) were higher in the rhizosphere for both total and EDTA-extractable fraction. Phragmites australis uptaked the highest concentrations in roots (e.g. ~66 mg kg?1 As, ~1,770 mg kg?1 Zn) but not in shoots, for which most of plant species showed low values for Zn (<300 mg kg?1) but not for Cd (>0.5 mg kg?1) or Pb (~20–40 mg kg?1). Vegetation distribution in the studied salt marsh looked to be more affected by salinity than by metal pollution. The free availability of water for plants and the incoming nutrient-enriched effluents which flow through the salt marsh may have hindered the metal(loid)s’ phytotoxicity. The phytomanagement of these polluted areas employing the spontaneous vegetation is a good option in order to improve the ecological indicators and to prevent the transport of pollutants to nearby areas.  相似文献   

8.
The aim of this study was to evaluate the relative performance of three nitrification inhibitors (NIs) viz. calcium carbide (CaC2), and plant derivatives of Pongamia glabra Vent. (karanj) and Melia azedarach (dharek) in regulating N transformations, inhibiting nitrification and improving N recovery in soil–plant systems. In the first experiment under laboratory incubation, soil was amended with N fertilizer diammonium phosphate [(NH4)2HPO4] at a rate of 200 mg N kg?1, N + CaC2, N + karanjin, and N + M. azedarach and incubated at 22 °C for 56 days period. Changes in total mineral N (TMN), NH4 +–N and NO3 ?–N were examined during the study. A second experiment was conducted in a glasshouse using pots to evaluate the response of wheat to these amendments. Results indicated that more than 92 % of the NH4 + initially present had disappeared from the mineral N pool by the end of incubation. Application of NIs i.e., CaC2, karanjin, and M. azedarach resulted in a significant reduction in the extent of NH4 + disappearance by 49, 32, and 13 %, respectively. Accumulation of NO3 ?–N was much higher in N amended soil 57 % compared to 11 % in N + CaC2, 13 % in N + karanjin, and 18 % in N + M. azedarach. Application of NIs significantly increased growth, yield, and N uptake of wheat. The apparent N recovery in N-treated plants was 20 % that was significantly increased to 38, 34, and 37 % with N + CaC2, N + karanjin, and N + M. azedarach, respectively. Among the three NIs tested, CaC2 and karanjin proved highly effective in inhibiting nitrification and retaining NH4 +–N in the mineral pool for a longer period.  相似文献   

9.
Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H2O 3.9–5.5), rich in organic matter (4–16 % C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1,066 and 1,589 mg kg?1, after adding 200 mg F L?1, which accounts for 53–80 % of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg?1). The fluoride sorption upon addition of 200 mg F L?1 correlated significantly (p < 0.05) with soil pH in water (r = ?0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12–22 % of sorbed fluoride and correlated (p < 0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r = ?0.51) and clay content (r = ?0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).  相似文献   

10.
The aim of this study was to investigate the influences of land use, parent materials (rock types) and soil properties on total arsenic and cadmium concentrations in the agricultural soils. A total of 87 surface (0–20 cm) soil samples were collected from four types of land use: irrigated farming, rangeland, dry farming and orchard. The average concentrations of the analyzed elements in topsoil were 84.426 mg As/kg and 3.289 mg Cd/kg. In addition, the pH, organic matter (OM), cation exchange capacity (CEC), soil grain sizes and CaCO3 were measured for each sample. The results indicated that land use had no significant effect on As and Cd concentrations. Our findings indicated that the Cd concentrations were influenced by bedrock composition, but for As there were no significant differences between various soil parent materials (bedrocks). Soil pollution was assessed on the basis of pollution index (PI), comprehensive pollution index (P n ) and geoaccumulation index (I geo). Calculated indices showed high-pollution levels for As and low- to moderate-pollution levels for Cd.  相似文献   

11.
This paper reports on hydrothermal synthesis and crystal structure refinement of dicadmium arsenate hydroxide, Cd2(AsO4)(OH), obtained at 220 °C and autogenous pressure. Its crystal structure is monoclinic, space group P21/a, with a = 13.097(3), b = 14.089(3), c = 10.566(2) Å, β = 108.38(3)°, V = 1850.2(6) Å3 (Z = 16). It is isotypic with the members of the triploidite group of minerals and synthetic compounds, and thus shows a close topological relationship with the triplite group. The complex framework contains edge- and corner-sharing CdO4(OH) and CdO4(OH)2 polyhedra, linked via corner-sharing to AsO4 tetrahedra (average As—O distances range between 1.682 and 1.688 Å). Four five-coordinated Cd sites are at the centers of distorted trigonal bipyramids (average Cd—O distances are between 2.225 and 2.251 Å), whereas the remaining four Cd sites have a distorted octahedral coordination environment (average Cd—O distances are between 2.297 and 2.320 Å). The positions of all the hydrogen atoms were located in a difference-Fourier map and refined with an isotropic displacement parameter. The hydrogen-bonds are weak to very weak. The unusual five-coordination of Cd is briefly discussed in relation to comparable minerals and compounds. Among triploidite-type compounds, Cd2(AsO4)(OH) is the member with the largest unit cell reported so far, and the second known arsenate member.  相似文献   

12.
The technique of diffusive gradients in thin films (DGT) was applied to obtain high-resolution vertical profiles of trace metals in sediment porewater of a eutrophic lake, Lake Chaohu. All sampling sediments were under anaerobic conditions with Eh values below 0, the redox potential profile in M4 was relatively stable, and higher Eh values in M4 than that in M1 were observed due to hydrodynamic effects. Fe, Mn and As exhibited closely corresponding profiles due to the co-release of Fe and Mn oxides and the reduction of As. Higher Fe and Mn concentrations and lower As concentrations were observed in M1 of the western half-lake than those in M4 of the eastern half-lake due to different sources and metal contamination levels in the two regions. Cu and Zn showed increasing concentrations similar to Mn and Fe at 1–2 cm depth of sediments, while DGT measured Co, Ni, Cd and Pb concentrations decreased down to 3–4 cm in the profiles. Co, Ni, Cu, Zn, Cd and Pb showed insignificant regional concentration variances in the western and eastern half-lakes. According to the R(C DGT/C centrifugation) values, the rank order of metal labilities decrease as follows: Fe (>1) > Cu, Pb, Zn (>0.9) > Co, Ni, Cd (>0.3) > Mn, As (>0.1).  相似文献   

13.
Pollution from mining activities is a significant problem in several parts of the Republic of Macedonia. A geochemical study of the surficial sediments of Lake Kalimanci in the eastern part of the Republic of Macedonia was carried out to determine their elemental compositions and to evaluate the pollution status of lake sediments by employing an enrichment factor (EF). The major and trace element contamination in surficial lake sediments was studied to assess the effects of metalliferous mining activities. The mean concentrations of major elements (wt%) Si 23.5, Al 7.9, Fe 6.6, Mg 1.3, Ca 3.8, Na 1.1, K 2.3, Ti 0.4, P 0.2, Mn 0.6 and trace elements ranged within Mo 1.0–4.6 mg kg?1, Cu 144.4–1,162 mg kg?1, Pb 1,874–16,300 mg kg?1, Zn 2,944–20,900 mg kg?1, Ni 21.7–79.3 mg kg?1, Cd 16.5–136 mg kg?1, Sb 0.6–3.6 mg kg?1, Bi 3.0–24,3 mg kg?1 and Ag 1.4–17.3 mg kg?1. The EF ranged within 0.12–590.3. Among which, Cd, Pb, Zn and As have extremely severe enrichment. The data indicate that trace elements had extremely high concentrations in Lake Kalimanci surficial sediments owing to the anthropogenic addition of contaminants.  相似文献   

14.
Heavy metal accumulation due to industrial activities has become a very sensitive issue for the survival of the aquatic life. Therefore, distributions of several heavy metals have been studied in the surface sediments of Tapti–Hazira estuary, Surat, to assess the impact of anthropogenic and industrial activities near estuary. Totally 60 sediment samples were collected from four different sites at Tapti–Hazira estuary, Surat from January 2011 to May 2011 and examined for metal contents. The average heavy metal load in the study area are found to be 43.28–77.74 mg/kg for Pb, 48.26–72.40 mg/kg for Cr, 117.47–178.80 mg/kg for Zn, 71.13–107.82 mg/kg for Ni, 123.17–170.52 mg/kg for Cu, 0.74–1.25 mg/kg for Cd, 14.73–21.69 mg/kg for Co. Calculated enrichment factors (EF) reveal that enrichment of Pb and Cd is moderate at all sites, whereas other metals Cr, Ni, Zn, Co, and Cu show significant to very high enrichment. Geo-accumulation index (I geo) results revealed that the study area is nil to moderately contaminated with respect to Cd, moderately to highly polluted with respect to Pb, Zn, and Cu and high to very highly polluted with respect to Co and Cr.  相似文献   

15.
This study examined the cell growth rate, lipid contents, lipid productivity, chlorophyll a concentration, and carbon dioxide tolerance of Chlorella vulgaris under various cultivation conditions. The pH, concentration of carbon dioxide in media, and light intensity variables were manipulated to obtain high lipid productivity. The optimum conditions were at pH 7.0, 2,930 lux, and 30 % carbon dioxide. Biomass concentration reached 1,288, 1,130, and 1,083 mg L?1 at 15, 30, and 50 % CO2 after 6 days, respectively, implying that this strain has appreciable tolerance to carbon dioxide. The highest concentration of chlorophyll a occurred at 2,930 lux and decreased with increasing light intensity gradually. The maximum specific growth rate was 3.25 day?1 based on the dry weight and 4.63 day?1 based on the cell number. The lipid content (45.68 %) and lipid productivity (86.03 mg day?1 L?1) obtained in this study are higher than reported values in literatures. Hence, C. vulgaris is a good candidate for subsequent research in biodiesel production under elevated carbon dioxide concentration by microalgae.  相似文献   

16.
In order to examine pressure–volume–temperature (P–V–T) relations for CaSiO3 perovskite (Ca-perovskite), high-temperature compression experiments with in situ X-ray diffraction were performed in a laser-heated diamond anvil cell (DAC) to 127 GPa and 2,300 K. We also employed an external heating system in the DAC in order to obtain P–V data at a moderate temperature of 700 K up to 113 GPa, which is the reference temperature for constructing an equation of state. The P–V data at 700 K were fitted to the second-order Birch–Murnaghan equation of state, yielding K 700,1bar = 207 ± 4 GPa and V 700,1bar = 46.5 ± 0.1 Å3. Thermal pressure terms were evaluated in the framework of the Mie–Grüneisen–Debye model, yielding γ 700,1bar = 2.7 ± 0.3, q 700,1bar = 1.2 ± 0.8, and θ 700,1bar = 1,300 ± 500 K. A thermodynamic thermal pressure model was also employed, yielding α700,1bar = 5.7 ± 0.5 × 10?5/K and (?K/?T) V  = ?0.010 ± 0.004 GPa/K. Computed densities along a lower mantle geotherm demonstrate that Ca-perovskite is denser than the surrounding lower mantle, suggesting that Ca-perovskite-rich rocks do not rise up through the lower mantle. One of such rocks might be a residue of partial melting of subducted mid-oceanic ridge basalt (MORB) at the base of the mantle. Since the partial melt is FeO-rich and therefore denser than the mantle, all the components of subducted MORB may not return to shallow levels.  相似文献   

17.
The structural evolution at high pressure of a natural 2M 1-phengite [(K0.98Na0.02)Σ=1.00(Al1.55Mg0.24Fe0.21Ti0.02)Σ=2.01(Si3.38Al0.62)O10(OH)2; a = 5.228(2), b = 9.057(3), c = 19.971(6)Å, β = 95.76(2)°; space group: C2/c] from the metamorphic complex of Cima Pal (Sesia Zone, Western Alps, Italy) was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to ~11 GPa. A series of 12 structure refinements were performed at selected pressures within the P range investigated. The compressional behaviour of the same phengite sample was previously studied up to ~25 GPa by synchrotron X-ray powder diffraction, showing an irreversible transformation with a drastic decrease of the crystallinity at P > 15–17 GPa. The elastic behaviour between 0.0001 and 17 GPa was modelled by a third-order Birch–Murnaghan Equation of State (BM-EoS), yielding to K T0 = 57.3(10) GPa and K′ = ?K T0/?P = 6.97(24). The single-crystal structure refinements showed that the significant elastic anisotropy of the 2M 1-phengite (with β(a):β(b):β(c) = 1:1.17:4.60) is mainly controlled by the anisotropic compression of the K-polyhedra. The evolution of the volume of the inter-layer K-polyhedron as a function of P shows a negative slope, Fitting the P–V(K-polyhedron) data with a truncated second-order BM-EoS we obtain a bulk modulus value of K T0(K-polyhedron) = 26(1) GPa. Tetrahedra and octahedra are significantly stiffer than the K-polyhedron. Tetrahedra behave as quasi-rigid units within the P range investigated. In contrast, a monotonic decrease is observed for the octahedron volume, with K T0 = 120(10) GPa derived by a BM-EoS. The anisotropic response to pressure of the K-polyhedron affects the P-induced deformation mechanism on the tetrahedral sheet, consisting in a cooperative rotation of the tetrahedra and producing a significant ditrigonalization of the six-membered rings. The volume of the K-polyhedron and the value of the ditrigonal rotation parameter (α) show a high negative correlation (about 93%), though a slight discontinuity is observed at P >8 GPa. α increases linearly with P up to 7–8 GPa (with ?α/?P ≈ 0.7°/GPa), whereas at higher Ps a “saturation plateau” is visible. A comparison between the main deformation mechanisms as a function of pressure observed in 2M 1- and 3T-phengite is discussed.  相似文献   

18.
The biosorption characteristics of Cd(II) and Cu(II) ions from aqueous solutions obtained using submerged aquatic plant (Myriophyllum spicatum) biomass were investigated in terms of equilibrium, kinetics, thermodynamics, and cation competition. Langmuir and Freundlich models were applied to describe the biosorption isotherm of metal ions by M. spicatum biomass and isotherm constants considering the most important parameter, pH. The variation of sorption isotherm constants showed pH dependence. The Langmuir and Freundlich models fitted the equilibrium data well. The maximum biosorption capacity (q m) of M. spicatum biomass was determined to be 29.07 mg/g for the Cd(II) ion at pH 5.0 and 12.12 mg/g for the Cu(II) ion at pH 6.0. Chi square analysis showed that the Freundlich model fitted the equilibrium data better than the Langmuir isotherm. Competition of Cd(II) and Cu(II) in a binary solution showed that the Langmuir monolayer capacity of Cd(II) decreased from 29.07 mg/g with only Cd(II) in solution to 12.02 mg/g in the presence of Cu(II). Kinetics results showed that the biosorption processes of both metal ions followed the pseudo-second-order kinetics well. The calculated thermodynamic parameters (?G 0, ?H 0, and ?S 0) showed that biosorption of Cd(II) and Cu(II) ions onto M. spicatum biomass was feasible, spontaneous, and endothermic in nature. Fourier transform infrared spectroscopy spectrum analysis revealed that Cd(II) and Cu(II) sorption was mainly ascribed to carboxyl, hydroxyl, amine, and C–N groups in M. spicatum.  相似文献   

19.
This study reported the first comprehensive research on identification of metal concentrations (Fe, Mg, Mn, Pb, Cd, Cr) in order to provide baseline data for future studies, identify possible sources, determine degree of pollution, and identify potential ecological risks of metals in surface sediments from Iran’s Choghakhor Wetland. The order of metal concentration was as follows: Fe > Mg > Mn > Pb > Cd > Cr, with mean concentrations of 6140.35, 1647.32, 289.03, 1.10, and 0.45 µg/g of dry weight, respectively. These results reveal that Choghakhor Wetland is not heavily polluted compared to other regions. The results of enrichment factor (EF) and geoaccumulation index (I geo) showed that Fe, Pb, Mg, Cr, and Mn presented low levels of contamination and probably originated from natural sources. On the other hand, the results of EF and I geo indices suggested that Cd concentrations in sediments of Choghakhor Wetland originated from anthropogenic sources. Based on the results of three sets of sediment quality guidelines, only Cd concentration in sediments of Choghakhor Wetland is a threat for aquatic organisms of Choghakhor Wetland. The results of multivariate analysis such as principal component analysis and cluster analysis showed that Fe–Mn, Cr–Mg, and Pb groups originated from natural sources, while Cd concentrations in sediments of Choghakhor Wetland originated from both natural and anthropogenic sources (mainly chemical fertilizers). To our knowledge, this is the first study about metal concentrations in sediments of Choghakhor Wetland, and because of low levels of these metals, these concentrations can be considered background levels for future investigation.  相似文献   

20.
The crystal chemistry across the garnet series is examined, and several systematic trends are reported. The crystal structure of three different cubic phases intergrown in a birefringent near end-member andradite from Namibia was refined by the Rietveld method, space group $ Ia\bar{3}d, $ Ia 3 ¯ d , and monochromatic synchrotron high-resolution powder X-ray diffraction data. Electron microprobe results indicate three phases with distinct compositions. The sample is birefringent, indicating that it is not cubic when observed optically. The reduced χ 2 and overall R (F 2) Rietveld refinement values are 1.655 and 0.0284, respectively, so the multi-phase refinement is excellent. The composition, weight %, unit-cell parameter (Å), distances (Å), and site-occupancy factors (sofs) are as follows: phase-1, Adr99, 88.5(1)  %, a = 12.06259(1), average 〈Ca–O〉 = 2.4310, Fe–O = 2.0189(4), Si–O = 1.6490(4) Å, Ca(sof) = 0.948(1), Fe(sof) = 0.934(1), and Si(sof) = 0.940(1). For phase-2: Adr71Grs28, 7.1(1) %, a = 12.00361(5), average 〈Ca–O〉 = 2.440, Fe–O = 1.979(3), Si–O = 1.641(3) Å, Ca(sof) = 0.913(5), Fe(sof) = 0.767(4), and Si(sof) = 0.932(5). For phase-3: Grs79Adr17, 4.4(1) %, a = 11.89719(4), average 〈Ca–O〉 = 2.404, Al–O = 1.935(4), Si–O = 1.667(3) Å, Ca(sof) = 0.944(6), Al(sof) = 1.069(7), and Si(sof) = 0.887(5). The dominant phase-1 (89 %; Adr99) is nearly end-member andradite, Ca3Fe 2 3+ Si3O12, which contains no cation order in the Ca(X) or Fe(Y) sites. The intergrowth of the three cubic phases causes considerable strain in the minor phases-2 and phases-3 that arise from different structural parameters and gives rise to strain-induced birefringence. For comparison, the results for an isotropic, single-phase, grossular–andradite garnet (Grs76Adr21) are also presented. The strain in the minor phases is about 3–5 times more than the unstrained dominant phase-1, or the unstrained single-phase grossular–andradite.  相似文献   

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