Energy transfer among Pb, Ce and Mn in fluorescent calcite from Kuerle, Xinjiang, China

Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb²⁺, Ce³⁺ and Mn²⁺, respectively, as activators. The Pb²⁺ excitation band is observed at 243 nm, and the Ce³⁺ excitation band at 295 nm. The Pb²⁺ excitation band is also observed by monitoring the Ce³⁺ fluorescence, and the Pb²⁺ and Ce³⁺ excitation bands, in addition to six Mn²⁺ excitation bands, are also observed by monitoring the Mn²⁺ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb²⁺ → Ce³⁺, (2) Pb²⁺ → Mn²⁺, (3) Ce³⁺ → Mn²⁺ and (4) Pb²⁺ → Ce³⁺ → Mn²⁺.     

Influence of extractable soil manganese on oxidation capacity of different soils in Korea

We examined the relationship between soil oxidation capacity and extractable soil manganese, iron oxides, and other soil properties. The Korean soils examined in this study exhibited low to medium Cr oxidation capacities, oxidizing 0.00–0.47 mmol/kg, except for TG-4 soils, which had the highest capacity for oxidizing added Cr(III) [>1.01 mmol/kg of oxidized Cr(VI)]. TG and US soils, with high Mn contents, had relatively high oxidation capacities. The Mn amounts extracted by dithionite-citrate-bicarbonate (DCB) (Mn^d), NH₂OH·HCl (Mn^h), and hydroquinone (Mn^r) were generally very similar, except for the YS1 soils, and were well correlated. Only small proportions of either total Mn or DCB-extractable Mn were extracted by NH₂OH·HCl and hydroquinone in the YS1 soils, suggesting inclusion of NH₂OH·HCl and hydroquinone-resistant Mn oxides, because these extractants are weaker reductants than DCB. No Cr oxidation test results were closely related to total Mn concentrations, but Mn^d, Mn^h, and Mn^r showed a relatively high correlation with the Cr tests (r = 0.655–0.851; P < 0.01). The concentrations of Mn^d and Mn^h were better correlated with the Cr oxidation tests than was the Mn^r concentration, suggesting that the oxidation capacity of our soil samples can be better explained by Mn^d and Mn^h than by Mn^r. The first component in principal components analysis indicated that extractable soil Mn was a main factor controlling net Cr oxidation in the soils. Total soil Mn, Fe oxides, and the clay fraction are crucial for predicting the mobility of pollutants and heavy metals in soils. The second principal component indicated that the presence of Fe oxides in soils had a significant relationship with the clay fraction and total Mn oxide, and was also related to heavy-metal concentrations (Zn, Cd, and Cu, but not Pb).     

Soil heavy-metal speciation and wheat phytotoxicity in the vicinity of an abandoned lead–zinc mine in Shangyu City,eastern China

Sixteen soil samples were collected from the vicinity of an abandoned lead–zinc mine in Shangyu City, eastern China, and the heavy-metal speciation and wheat phytotoxicity in the soils were studied. The results showed that the concentrations of free Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were highly variable and ranged from <0.01 to 0.32, 0.06 to 10.62, <0.01 to 1.40 and 0.02 to 37.10 μmol l⁻¹, respectively. The concentrations of soluble Cu, Zn, Cd and Pb ranged from 0.38 to 3.24, 0.72 to 78.74, <0.01 to 1.95 and 0.15 to 639.34 μmol l⁻¹, respectively. The general trend of mean solid/liquid partition coefficient and percentage of free metal ion to total soluble metal concentration were Cu > Pb > Zn > Cd and Cd > Zn > Cu > Pb, respectively. Stepwise multiple linear regression with pH, log(total metal) and log(organic matter) showed that log(total metal) was an important factor that controlled log(free metal ion) and log(soluble metal). Of the variability in log(free Cu²⁺), log(free Cd²⁺) and log(free Pb²⁺), 55.2, 58.6 and 64.3% could be explained by log(total Cu), log(total Cd) and log(total Pb) alone, respectively. Of the variability in log(soluble Cu) and log(soluble Cd), 77.1 and 72.5% could be explained by log(total Cu) and log(total Cd) alone, respectively. Wheat root length was controlled by the various metals with different free and soluble concentrations, and 99.2% of the variability in root length could be explained by concentrations of free and soluble Pb, soluble Cu and total Zn in the soils.     

Removal of Pb2+ from aqueous solutions using two Brazilian rocks containing zeolites

The removal of Pb²⁺ from aqueous solution by two Brazilian rocks that contain zeolites—amygdaloidal dacite (ZD) and sandstone (ZS)—was examined by batch experiments. ZD contains mordenite and ZS, stilbite. The effects of contact time, concentration of metal in solution and capacity of Na⁺ to recover the adsorbed metals were evaluated at room temperature (20°C). The sorption equilibrium was reached in the 30 min of agitation time. Both materials removed 100% of Pb²⁺ from solutions at concentrations up to 50 mg/L, and at concentrations larger than 100 mg/L of Pb²⁺, the adsorption capacity of sandstone was more efficient than that of amygdaloidal dacite due to the larger quantities and the type of zeolites (stilbite) in the cement of this rock. All adsorbed Pb²⁺ was easily replaced by Na⁺ in both samples. The analysis of the adsorption models using nonlinear regression revealed that the Sips and the Freundlich isotherms provided the best fit for the ZS and ZD experimental data, respectively, indicating the heterogeneous adsorption surfaces of these zeolites.     

Heavy metal concentrations and their possible sources in paddy soils of a modern agricultural zone,southeastern China

In a typical modern agricultural Zone of southeastern China, Haining City, 224 topsoil samples were collected from paddy fields to measure the total concentrations of copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr), mercury (Hg), arsenic (As) and cobalt (Co). The total concentrations ranged from 15.30 to 78.40 mg kg⁻¹ for Cu, 20.10 to 41.40 mg kg⁻¹ for Pb, 54.98 to 224.4 mg kg⁻¹ for Zn, 0.04 to 0.24 mg kg⁻¹ for Cd, 54.90 to 197.1 mg kg⁻¹ for Cr, 0.03 to 0.61 mg kg⁻¹ for Hg, 3.44 to 15.28 mg kg⁻¹ for As, and 7.17 to 19.00 mg kg⁻¹ for Co. Chemometric techniques and geostatistics were utilized to quantify their spatial characteristics and define their possible sources. All eight metals had a moderate spatial dependency except that Pb had a strong spatial dependency. Both factor analysis and cluster analysis successfully classified the eight metals into three groups or subgroups, the first group included Cu, Zn and Cr, the second group included Cd, As and Co, and the last group included Pb and Hg. The Cu, Zn and Cr concentrations in majority samples were higher than their local background concentrations and they were highly correlated (r > 0.80), indicating that they had similar pollution source and anthropic factor controlled their spatial distribution; the Cd, As and Co concentrations in majority samples were lower than their local background concentrations, indicating that the source of these elements was mainly controlled by natural factors; the mean concentration of Pb exhibited generally low level, close to its local background concentration, the Hg concentration in about half of samples was higher than its local background concentration, and they were poor correlated with the other metals, indicating that the source of Pb and Hg was common controlled by natural factor and anthropic factor.     

Trace elements contamination of agricultural soils affected by sulphide exploitation (Iberian Pyrite Belt,Sw Spain)

Agricultural soils of the Riotinto mining area (Iberian Pyrite Belt) have been studied to assess the degree of pollution by trace elements as a consequence of the extraction and treatment of sulphides. Fifteen soil samples were collected and analysed by ICP-OES and INAA for 51 elements. Chemical analyses showed an As–Cu–Pb–Zn association related with the mineralisation of the Iberian Pyrite Belt. Concentrations were 19–994 mg kg⁻¹ for As, 41–4,890 mg kg⁻¹ for Pb, 95–897 mg kg⁻¹ for Zn and of 27–1,160 mg kg⁻¹ for Cu. Most of the samples displayed concentrations of these elements higher than the 90th percentile of the corresponding geological dominium, which suggests an anthropogenic input besides the bedrock influence. Samples collected from sediments were more contaminated than leptosols because they were polluted by leachates or by mining spills coming from the waste rock piles. The weathering of the bedrock is responsible for high concentrations in Co, Cr and Ni, but an anthropogenic input, such as wind-blown dust, seems to be indicative of the high content of As, Cu, Pb and Zn in leptosols. The metal partitioning patterns show that most trace elements are associated with Fe amorphous oxy-hydroxides, or take part of the residual fraction. According to the results obtained, the following mobility sequence is proposed for major and minor elements: Mn, Pb, Cd, > Zn, Cu > Ni > As > Fe > Cr. The high mobility of Pb, Cu and Zn involve an environmental risk in this area, even in soils where the concentrations are not so high.     

Hydrochemical and microbiological quality of groundwater in West Thrace Region of Turkey

The aim of this study was to do a preliminary assessment of the hydrochemical and microbial groundwater quality of the West Thrace region. Forty samples of groundwater collected from Edirne (Site 1) to Gelibolu (Site 2) were assessed for their suitability for human consumption. As³⁻ was non-detectable in all the groundwater and Zn²⁺, Pb²⁺, F⁻, Cu²⁺, NH₄⁺, Cn⁻ PO₄³⁻ and Cl⁻ were all below their respective European Union drinking water directive (EU-DWD) and Turkish food codex-drinking water directive (TFC-DWD). Maximum Acceptable Concentrations (MAC) Ni²⁺, Pb²⁺, Cd²⁺, Mg²⁺, Mn²⁺, and Ca²⁺ levels were detected in upper maximum acceptable concentrations 77.5, 42.5, 35.0, 50.0, 50.0, and 32.5% of the groundwater samples, respectively. However, in terms of Cr³⁺, Ni²⁺ and Pb²⁺, the differences between groundwaters of Sites 1 and 2 were significant (p < 0.05). Eight water samples (20%) had HPC exceeding the EU and Turkish water directive limit 20 CFU (Colony Forming Unit)/ml in drinking water and the maximum bacteria count recorded was 44 CFU/ml. Total coliforms, thermotolerant coliforms, E. coli, Enterococcus spp., Salmonella sp., Staphylococcus spp. and P. aeruginosa were detected in 25, 17.5, 15, 47.5, 15, 27.5, and 15% of the groundwater samples, respectively. Furthermore, heavy metals and trace elements were found after chemical analyzes in most samples. The pollution of groundwater come from a variety of sources, Meric and Ergene rivers, including land application of agricultural chemicals and organics wastes, infiltration of irrigation water, septic tanks, and infiltration of effluent from sewage treatment plants, pits, lagoons and ponds used storage.     

Ion exchange properties of manganese and iron minerals in oceanic micronodules

The results of experimental studies of ion exchange properties of manganese and iron minerals in micronodules (MN) from diverse bioproductive zones of the World Ocean are considered. It was found that the sorption behavior of these minerals is similar to that of ore minerals from ferromanganese nodules (FMN) and low-temperature hydrothermal crusts. The exchange complex of minerals in the MN includes the major (Na⁺, K⁺, Ca²⁺, Mg²⁺, and Mn²⁺) and the subordinate (Ni²⁺, Cu²⁺, Co²⁺, Pb²⁺, and others) cations. Reactivity of theses cations increases from Pb²⁺ and Co²⁺ to Na⁺ and Ca²⁺. Exchange capacity of MN minerals increases from the alkali to heavy metal cations. Capacity of iron and manganese minerals in the oceanic MN increases in the following series: goethite < goethite + birnessite < todorokite + asbolane-buserite + birnessite < asbolane-buserite + birnessite < birnessite + asbolane-buserite < birnessite + vernadite Fe-vernadite + Mn-feroxyhyte. The data obtained supplement the available information on the ion exchange properties of oceanic ferromanganese sediments and refine the role of sorption processes in the redistribution of metal cations at the bottom (ooze) water-sediment interface during the MN formation and growth.     

Pollution caused by metallic fragments introduced into soils because of World War I activities

 The influence of parent rock and soil material on the corrosion rate of metallic fragments that remained in soil after World War I in the Soča front area (Slovenia), as well as the corrosion products of these fragments, were studied. The results of corrosion tests did not indicate appreciable differences in corrosion rates between various corrosion media. Consequently, the corrosion rates are influenced mostly by soil aeration, soil humidity and also by microstructures of alloys. Soil type seems to have the most influence on corrosion products. For the pH and Eh ranges that prevail in the studied soils, goethite is the only stable iron mineral. Lead minerals are not stable, and lead, in a Pb²⁺ cation form, is probably adsorbed onto some minerals – especially goethite – or is bound with organic matter. In distric brown soil, lead stays in the cation form as Pb²⁺ because of high soil acidity. Cuprite is stable in rendzina and brown soil on limestone, whereas in distric brown soil copper stays in solution as Cu²⁺. Received: 7 October 1999 · Accepted: 8 March 2000     

Sources of deep groundwater salinity in the southwestern zone of Bangladesh

Twenty groundwater samples were collected from two different areas in Satkhira Sadar Upazila to identify the source of salinity in deep groundwater aquifer. Most of the analyzed groundwater is of Na–Cl–HCO₃ type water. The trends of anion and cation are Cl⁻ > HCO₃ ⁻ > NO₃ ⁻ > SO₄ ²⁻ and Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, respectively. Groundwater chemistry in the study area is mainly governed by rock dissolution and ion exchange. The dissolved minerals in groundwater mainly come from silicate weathering. The salinity of groundwater samples varies from ~1 to ~5%, and its source is possibly the paleo-brackish water which may be entrapped during past geologic periods.     

Hydrogeochemistry and pollution assessment of quaternary–tertiary aquifer in the Liwa area,United Arab Emirates

This study presents the data on the hydrochemical characteristics and isotope chemistry of Liwa aquifer, which could be useful to clarify the hydrochemical facies and hydrogeological regime in the study area. Electric conductivity and total dissolved solid values show that the investigated water is slightly brackish, due to the effect of evaporation and the occurrences of evaporite rocks in the adjacent Sabkhas of Abu Dhabi. Major cations and anions arranged according to their decreasing concentrations are: Na⁺ > Ca⁺² > K⁺ > Mg⁺² and Cl⁻ > HCO₃ ⁻ > SO₄⁻², respectively. As sodium is the dominate cation and chloride is the prevailing anion, hydrochemically the groundwater of Liwa can be classified as Na–Cl rich, predominantly chloridic. Ion concentrations increase towards the northeast and presumably coincide with the lithological sources of ions. Factors affecting the hydrochemistry of the groundwater of the investigated area include the effect of weathering of soil and rocks, evaporation and agricultural activities. Stable isotopes of oxygen and hydrogen show that the shallow aquifers contain a single water type that originated in a distinct climatic regime. This water type deviates from the local meteoric water line, as well as from the Eastern Mediterranean Meteoric Water Line, suggesting potential evaporation of recharged water prior to infiltration. The waters are poor in tritium, and thus can be considered generally as indication for recharge prior to 1952. The degradation of groundwater quality can be attributed to evaporation and agricultural practices in most cases.     

Microelectrode Study of Oxygen Uptake and Organic Matter Decomposition in The Sediments of Xiamen Western Bay

Sediment cores were sampled from Xiamen Western Bay at five sites during the summer and winter of 2006 and Hg–Au microelectrodes were used to make on board measurements of the concentration gradients of dissolved oxygen, Mn²⁺, and Fe²⁺ within the sediments. The O₂ concentrations decreased sharply from about 200 μmol L⁻¹ in the bottom seawater to zero within a depth of a few millimeters into the sediment. Dissolved Mn²⁺ was detected below the oxic zones with peak concentrations up to 600 μmol L⁻¹, whereas dissolved Fe²⁺ had peak concentrations up to 1,000 μmol L⁻¹ in deeper layers. The elemental contents of organic carbon and nitrogen within the sediments were analyzed and their C/N ratios were in the range of 9.0 to 10.1, indicative of heavy terrestrial origin. Sediments from two sites near municipal wastewater discharge outlets had higher organic contents than those from the other sites. These high organic contents corresponded to shallow O₂ penetration depths, high dissolved Mn²⁺ and Fe²⁺ concentrations, and negative redox potentials within the sediments. This indicated that the high organic matter content had promoted microbial respiration within the sediments. Overall, the organic content did not show any appreciable decrease with increasing sediment depths, so a quadratic polynomial function was used to fit the curve of O₂ profiles within the sediments. Based on the O₂ profiles, O₂ fluxes across the seawater and sediment interface were estimated to be in the range 6.07 to 14.9 mmol m⁻² day⁻¹, and organic carbon consumption rates within the surface sediments were estimated to be in the range 3.3 to 20.8 mgC cm⁻³ a⁻¹. The case demonstrated that biogeochemistry within the sediments of the bay was very sensitive to human activities such as sewage discharge.     

The crystal structure of arsentsumebite, Pb2Cu[(As, S)O4]2(OH)

Summary The crystal structure of arsentsumebite, ideally, Pb₂Cu[(As, S)O₄]₂(OH), monoclinic, space group P2₁/m, a = 7.804(8), b = 5.890(6), c = 8.964(8) ?, β = 112.29(6)°, V = 381.2 ?³, Z = 2, d_calc. = 6.481 has been refined to R = 0.053 for 898 unique reflections with I> 2σ(I). Arsentsumebite belongs to the brackebuschite group of lead minerals with the general formula Pb₂ Me(XO₄)₂(Z) where Me = Cu²⁺, Mn²⁺, Zn²⁺, Fe²⁺, Fe³⁺; X = S, Cr, V, As, P; Z = OH, H₂O. Members of this group include tsumebite, Pb₂Cu(SO₄)(PO₄)(OH), vauquelinite, Pb₂Cu(CrO₄)(PO₄)(OH), brackebuschite, Pb₂ (Mn, Fe)(VO₄)₂(OH), arsenbracke buschite, Pb₂(Fe, Zn)(AsO₄)₂(OH, H₂O), fornacite, Pb₂Cu(AsO₄)(CrO₄)(OH), and feinglosite, Pb₂(Zn, Fe)[(As, S)O₄]₂(H₂O). Arsentsumebite and all other group members contain M = M–T chains where M = M means edge-sharing between MO₆ octahedra and M–T represents corner sharing between octahedra and XO₄ tetrahedra. A structural relationship exists to tsumcorite, Pb(Zn, Fe)₂(AsO₄)₂ (OH, H₂O)₂ and tsumcorite-group minerals Me(1)Me(2)₂(XO₄)₂(OH, H₂O)₂. Received June 24, 2000; revised version accepted February 8, 2001     

Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain,Bangladesh

The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from 8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r ² = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top, passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and 5,000 years BP (¹⁴C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed onto Fe oxides in aquifer sediments.     

Correlative and comparative characterization of main ion concentrations in laterite groundwater in semi-arid northern Burkina Faso

About 24 samples from hand-dug wells and boreholes were used to characterize concentrations of the main inorganic ions in a laterite environment under semi-arid climatic conditions in Tikaré, northern Burkina Faso. It was found that the most represented groundwater anion in groundwater was HCO₃ ⁻ with average levels of 49.1 mg/L in the dry season and 33.5 mg/L in the rainy season. The most represented cation was Ca²⁺ with mean concentrations of 13.7 and 9.5 mg/L, respectively. The main processes, which influence the concentrations of these ions, are evaporation (dry season), local enrichment of recharge water in some elements, ion exchange and fixation by clay minerals (in case of K⁺). The best correlations were found between Ca²⁺ and Mg²⁺ (r = 0.95), Cl⁻ and Na⁺ (r = 0.95), HCO₃ ⁻ and Mg²⁺ (r = 0.89), HCO₃ ⁻ and Ca²⁺ (r = 0.89), and between HCO₃ ⁻ and Na⁺ (r = 0.80). In general, the quality of the groundwater from the different wells sampled for this study was good enough to serve as drinking water. However, there were situations where the quality of water was polluted because of anthropogenic contaminants (mainly NO₃ ⁻, K⁺, Cl⁻) from septic tanks and manure pits located in the vicinity of some sampled wells. In addition, application of fertilizers also represents a potential anthropogenic contamination source with regard to SO₄ ²⁻, Ca²⁺, K⁺, Na⁺, and Mg²⁺. Considering the high concentrations of SO₄ ²⁻, Mg²⁺, Na⁺ and Ca²⁺ found in one borehole, the deeper, fractured aquifers were also likely to be enriched in these elements. In contrast, the shallow aquifers are likely to be contaminated with Cl⁻, NO₃ ⁻ and K⁺. Cl⁻ and K⁺ seem to be locally present in recharge water as shown by their relative higher mean concentrations in the rainy season samples.     

EPR study of coordination of Ag and Pb cations in BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals and barium borate glasses

It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study α-and β-BaB₂O₄ crystals and glasses of 45·BaO × 55·B₂O₃ and 40·BaO × 60·B₂O₃ (mol%) composition activated by Ag⁺ and Pb²⁺ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In α-and β-BaB₂O₄ crystals and glasses the EPR centers Ag²⁺, Ag⁰, Pb⁺, Pb³⁺, and hole centers of O⁻ type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is shown that Pb³⁺ ions in β-BaB₂O₄ crystals occupy Ba²⁺ position in an irregular polyhedron from the eight oxygen, whereas in α-BaB₂O₄ crystals they occupy Bа₂ position in a sixfold coordination. Pb⁺ ions in α-BaB₂O₄ crystals occupy Bа₁ position in a ninefold coordination from oxygen. In barium borate glasses, Pb³⁺ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It is assumed that the established difference in the structural position of Pb³⁺ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and “free” structure-forming cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare their bond lengths with experimental data.     

Mobility and ecological risk assessment of heavy metals in surface sediments of Xiamen Bay and its adjacent areas,China

Xiamen Bay (XMB) has received substantial loadings of pollutants from industrial and municipal wastewater discharged since the 1980s. To assess ecological risks and the current spatial changes of metal contaminants in bottom surface sediments, 12 samples were collected. Samples were subjected to a total digestion technique and analyzed by ICP–OES for Cu, Pb, Zn, Cr, and Cd, and by AFS for Hg and As. Among these metals, Zn had the highest values (68–268 mg kg⁻¹), followed by Pb (27–71 mg kg⁻¹), and lower concentrations were found for Cd (42–1,913 μg kg⁻¹) and Hg (0–442 μg kg⁻¹). In comparison with the average crustal abundance values, the results indicated that nearly half of the sediment samples of XMB and its adjacent areas were contaminated by Cd, Pb, Zn, and As. Furthermore, based on the modified BCR sequential extraction procedure, the chemical speciation of heavy metals (Cd, Cr, Cu, Pb, Zn, Hg, and As) in selected sediment samples were evaluated in this study. Data from BCR sequential extractions indicated that Cd posed a medium ecological risk, whereas, Cr posed low risk since its exchangeable and carbonate fractions were below 4%, and the mobility of heavy metals in XMB decreased in the order Cd > Pb > Cu > Zn > Hg > As > Cr. By applying mean effects range median quotients (mERMQ), the results showed that Yuandang Lagoon with mERMQ value >0.5 would be expected to have the greatest potential toxic risk in amphipod within XMB and its adjacent areas.     

Quantitative spatial characteristics and environmental risk of toxic heavy metals in urban dusts of Shanghai,China

Associated with the rapid urbanization and industrialization, most of the urban parks and recreational areas in Shanghai are built close to major roads or industrial areas, where they are subject to many potential pollution source, including automobile exhaust and factory emissions. Urban dusts, containing many toxic heavy metals such as Pb, Cr, Cd, Hg and As, are one of main contributors for environmental pollution. In this study, 261 dust samples were collected from two different localities (streets and parks) in the urban area of Shanghai, China. Pb and Cr concentrations of all samples were determined by atomic adsorption spectrophotometer analyzer, and Cd, As and Hg concentrations in 74 samples by atomic fluorescence spectroscopy. The mean concentrations of Pb, Cr, Cd, As and Hg are 287, 157, 1.24, 8.73 and 0.16 mg kg⁻¹, respectively. Each heavy metal shows a wide range of concentration values. In comparison with heavy metal background values of soil in Shanghai, urban dusts have elevated metal concentrations as a whole, except those of As. The concentrations of Pb, Cr, Cd, As and Hg are 11.3, 2.1, 10.3, 0.997, 1.7 times of the soil background values, respectively. Compared with the global mean concentrations, Cr concentration in urban dusts is slightly higher. Pb, Cr and Hg show normal distribution after logarithmic transformation. Pb, Cr, Cd, As and Hg have second-order variation trends of the spatial distribution. The spatial distribution features of five toxic heavy metals, in general, illustrate relatively high levels within the regions of the inner-city ring highway and southwestern Shanghai. Cr and Cd are higher in Baoshan industrial park and the shipbuilding industries regions. The order of environmental risk is Pb > Cd > Cr > Hg > As. Pb and Cd have the highest risk for environment pollution and human health among the five metals. The pollutant sources of toxic heavy metals in Shanghai urban dusts are preliminarily concluded as follows: As may have mainly a natural source. Burning of coal has become the main source of Hg pollution. Pb, Cr and Cd have three sources, traffic, building construction, and weathering corrosion of building materials.     

The spatial characteristics and pollution levels of metals in urban street dust of Beijing,China

The components and concentrations of metals in street dust are indictors of environmental pollution. To explore the pollution levels of Cd, Cr, Cu, Mn, Ni and Pb in street dust and their spatial distribution characteristics, 220 dust samples were collected in a grid pattern from urban street surfaces in Beijing. Multivariate statistics and spatial analyses were adopted to investigate the associations between metals and to identify their pollution patterns. In comparison with the soil background values, elevated metal concentrations were found, except those for Mn and Ni. The results of the geo-accumulation index (I_geo) and the potential ecological risk index (Erⁱ) of the metals revealed the following orders: Cd > Cu > Cr > Pb > Ni > Mn and Cd > Cu > Pb > Cr > Ni. Levels of I_geo ranging from 0 to 5 were found and about 80% of the samples were below the moderately polluted level. The Erⁱ values of single elements were within the low ecological risk level in most sampling sites. Most of the metals in the street dust of Beijing were statistically significantly correlated. It is hard to clearly identify the sources of each metal in the street dust since local environments are very complex. Cadmium, Cu, Cr, Mn and Pb showed medium spatial autocorrelations within the sampling region. Similar spatial distribution patterns were observed for Cu, Cr and Pb, and these metals had relatively high spatial variabilities and were enriched in the center of the city with several peaks scattered in the suburbs. Metal pollution anomalies were identified by using cluster and outlier analyses. Locations identified as clusters with high values indicated non-point source pollution, while locations identified as outliers with high values indicated point source pollution. Traffic, construction, and other human activities influenced these high values. In addition, the locations identified as outliers with low values in urban areas might benefit from less transportation and better management.     

Evaluation of groundwater quality with emphasis on fluoride concentration in Nalbari district,Assam, Northeast India

This study was carried out to analyze groundwater quality in selected villages of Nalbari district, Assam, India, where groundwater is the main source of drinking water. 40 groundwater samples collected from hand pumps and analyzed for pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ⁻, SO₄ ²⁻, Cl⁻ and F⁻. Chemical analysis of the groundwater showed that mean concentration of cations in (mg/L) is in the order Ca²⁺ > Mg²⁺ > Na⁺ > K⁺ while for anions it is HCO₃ ⁻ > Cl⁻ > SO₄ ²⁻ > F⁻. Fluoride concentration was recorded in the range of 0.02–1.56 mg/L. As per the desirable and maximum permissible limits for fluoride in drinking water recommended by WHO and by Bureau of Indian Standards (BIS), which is 1.5 mg/L, the groundwater of about 97% of the samples were found to be suitable for drinking purpose. The suitability of the groundwater for irrigation purpose was investigated by some determining factors such as sodium adsorption ratio, soluble sodium percentage, Kelly’s ratio and electrical conductivity. The value of the sodium absorption ratio and electrical conductivity of the groundwater samples were plotted in the US Salinity laboratory diagram for irrigation water. Most of the groundwater samples fall in the field of C2S1 and C3S1 indicating medium to high salinity and low sodium water, which can be used for irrigation on almost all types of soil with little doubt of exchangeable sodium. The hydrochemical facies shows that the groundwater is Ca-HCO₃ type.