Effects of cations and anions on iron and manganese sorption and desorption capacity in calcareous soils from Iran

This study investigated the effect of cations and anions on the sorption and desorption of iron (Fe) and manganese (Mn) in six surface calcareous soil samples from Western Iran. Six 10 mM electrolyte background solutions were used in the study, i.e., KCl, KNO₃, KH₂PO₄, Ca(NO₃)₂, NaNO₃, and NH₄NO₃. NH₄NO₃ and NaNO₃ increased the soil retention of Fe and Mn, whereas Ca(NO₃)₂ decreased the soil retention of Fe and Mn. Iron and Mn sorption was decreased by NO₃ ^? compared with H₂PO₄ ^? or Cl^?. The Freundlich equation adequately described Fe and Mn adsorption, with all background electrolytes. The Freundlich distribution coefficient (K _F) decreased in the order H₂PO₄ ^? > Cl^? > NO₃ ^? for Mn and H₂PO₄ ^? > NO₃ ^? > Cl^? for Fe. The highest sorption reversibility was for Fe and Mn in competition with a Ca²⁺ background, indicating the high mobility of these two cations. A MINTEQ speciation solubility model showed that Fe and Mn speciation was considerably affected by the electrolyte background used. Saturation indices indicated that all ion background solutions were saturated with respect to siderite and vivianite at low and high Fe concentrations. All ion background solutions were saturated with respect to MnCO_3(am), MnHPO₄, and rhodochrosite at low and high Mn concentrations. The hysteresis indices (HI) obtained for the different ion backgrounds were regressed on soil properties indicating that silt, clay, sand, and electrical conductivity (EC) were the most important soil properties influencing Fe adsorption, while cation exchange capacity (CEC), organic matter (OM), and Mn-DTPA affected Mn adsorption in these soils.     

Production of Reactive Oxygen Species in the Rhizosphere of a <Emphasis Type="Italic">Spartina-</Emphasis>Dominated Salt Marsh Systems

This paper reports the presence of a metastable mixture of Fe(II), O₂, superoxide and hydrogen peroxide in sediment pore water in organic carbon-rich sediments in Spartina alterniflora-dominated salt marsh systems. Field measurements at two different estuarine sites in South Carolina (one heavily urbanized and a protected research reserve) showed a broad region of reactive oxygen species (ROS) production more than 15 cm below the sediment surface within and immediately adjacent to the rhizospheres of S. alterniflora. Dissolved Fe(II) was positively correlated with hydrogen peroxide indicating a possible abiotic pathway to ROS production (r ² = 0.94). The null hypothesis was tested that Fe(II) inventories were maintained by protective ligands and thus unreactive with respect to O₂ consumption and ROS production. The addition of an Fe-binding ligand, DTPA, resulted in rapid decline of ROS in pore water, indicating that Fe(II) was labile. The half-life of superoxide under the measured solution conditions was calculated and found to be less than a second. The combination of high lability and persistent ROS was interpreted to indicate a high rate of Fe(II) and O₂ supply to the pore water. The ²²⁴Ra/²²⁸Th disequilibrium was measured to determine the potential for advective mass transfer of dissolved oxygen via pore water exchange. The estimated pore water exchange of 54 L m^?2 day^?1 was significant but could not support the measured production of ROS alone, the direct exchange of O₂ from the S. alterniflora root system may have contributed significantly to ROS production in the sediments.     

Analysis of long-term bacterial vs. chemical Fe(III) oxide reduction kinetics

Data from studies of dissimilatory bacterial (10⁸ cells mL⁻¹ of Shewanella putrefaciens strain CN32, pH 6.8) and ascorbate (10 mM, pH 3.0) reduction of two synthetic Fe(III) oxide coated sands and three natural Fe(III) oxide-bearing subsurface materials (all at ca. 10 mmol Fe(III) L⁻¹) were analyzed in relation to a generalized rate law for mineral dissolution (J_t/m₀ = k′(m/m₀)^γ, where J_t is the rate of dissolution and/or reduction at time t, m₀ is the initial mass of oxide, and m/m₀ is the unreduced or undissolved mineral fraction) in order to evaluate changes in the apparent reactivity of Fe(III) oxides during long-term biological vs. chemical reduction. The natural Fe(III) oxide assemblages demonstrated larger changes in reactivity (higher γ values in the generalized rate law) compared to the synthetic oxides during long-term abiotic reductive dissolution. No such relationship was evident in the bacterial reduction experiments, in which temporal changes in the apparent reactivity of the natural and synthetic oxides were far greater (5-10 fold higher γ values) than in the abiotic reduction experiments. Kinetic and thermodynamic considerations indicated that neither the abundance of electron donor (lactate) nor the accumulation of aqueous end-products of oxide reduction (Fe(II), acetate, dissolved inorganic carbon) are likely to have posed significant limitations on the long-term kinetics of oxide reduction. Rather, accumulation of biogenic Fe(II) on residual oxide surfaces appeared to play a dominant role in governing the long-term kinetics of bacterial crystalline Fe(III) oxide reduction. The experimental findings together with numerical simulations support a conceptual model of bacterial Fe(III) oxide reduction kinetics that differs fundamentally from established models of abiotic Fe(III) oxide reductive dissolution, and indicate that information on Fe(III) oxide reactivity gained through abiotic reductive dissolution techniques cannot be used to predict long-term patterns of reactivity toward enzymatic reduction at circumneutral pH.     

Sorption and desorption of mercury(II) in saline and alkaline soils of Bahía Blanca, Argentina

The objective of this work was to study sorption–desorption and/or precipitation–dissolution processes of Hg(II) compounds considering an eventual contact of soils with Hg-bearing wastes. In addition, this study contributes new data about Hg(II) chemistry in alkaline systems. Saline and alkaline soils with low organic matter (<1 %) and high clay content (60–70 %) were obtained near a chlor-alkali plant. Batch techniques were used to perform the experiments using 0.1 M NaNO₃ solutions. Total Hg(II) concentrations ranged from 6.2 × 10^?8 to 6.3 × 10^?3 M. Sorption of Hg(II) was evaluated at two concentration ranges: (a) 6.2 × 10^?8 to 1.1 × 10^?4 M, and (b) 6.4 × 10^?4 to 6.3 × 10^?3 M. At low Hg(II) concentrations, adsorption occurred with a maximum sorption capacity ranging from 4 to 5 mmol/kg. At high Hg(II) concentrations, sorption–precipitation reactions occurred and maximum sorption capacity ranged from 17 to 31 mmol/kg. The distribution of Hg(II) hydrolysis products showed that Hg(OH)₂ was the predominant species under soil conditions. According to sorption experiments, X-ray diffraction and chemical speciation modelling, the presence of Hg(OH)₂ in the interlayer of the interstratified clay minerals can be proposed. Hg(OH)₂ was partially desorbed by repeated equilibrations in 0.1 M NaNO₃ solution. Desorption ranged from 0.1 to 0.9 mmol/kg for soils treated with 5.8 × 10^?5 M Hg(II), whereas 2.1–3.8 mmol/kg was desorbed from soils treated with 6.3 × 10^?3 M Hg(II). Formation of soluble Hg(II) complexes was limited by low organic matter content, whereas neutral Hg(OH)₂ was retained by adsorption on clay mineral surfaces.     

Iron release in aqueous environment by fresh volcanic ash from Mount Etna (Italy) and Popocatépetl (Mexico) volcanoes

In this study, we performed leaching experiments for timescales of hours-to-months in deionized water on fresh volcanic ash from Mt. Etna (Italy) and Popocatépetl (Mexico) volcanos to monitor Fe release as a function of ash mineral chemistry and size, with the aim of clarifying Fe release mechanisms and eventually evaluating the impact of volcanic ash on marine and lacustrine environments. To define sample mineralogy and Fe speciation, inclusive characterization was obtained by means of XRF, SEM, XRPD, EELS and Mössbauer spectroscopies. For Etna and Popocatépetl samples, glass proportions were quantified at 73 and 40%, Fe₂O₃ total contents at 11.6–13.2 and 5.8 wt%, and Fe³⁺/Fe_Tot ratios at 0.33 and 0.23, respectively. Leaching experiments showed that significant amounts of iron, ~?30 to 150 and ~?750 nmol g^?1 l^?1 for pristine Etna and Popocatépetl samples, respectively, are released within the first 30 min as a function of decreasing particle size (from 1 to 0.125 mm). The Popocatépetl sample showed a very sustained Fe release (up to 10 times Etna samples) all along the first week, with lowest values never below 400 nmol g^?1 l^?1 and a maximum of 1672 nmol g^?1 l^?1 recorded after 5 days. This sample, being composed of very small particles (average particle size 0.125 mm) with large surface area, likely accumulated large quantities of Fe-bearing sublimates that quickly dissolved during leaching tests, determining high Fe release and local pH decrease (that contributed to release more Fe from the glass) at short timescale (hours-to-days). The fractional Fe solubility (Fe_S) was 0.004–0.011 and 0.23% for Etna and Popocatépetl samples, respectively, but no correlation was found between Fe released in solution and either ash Fe content, glass/mineral ratio or mineral assemblage. Results obtained suggest that volcanic ash chemistry, mineralogy and particle size assume a relevant role on Fe release mostly in the medium-to-long timescale, while Fe release in the short timescale is dominated by dissolution of surface sublimates (formed by physicochemical processes occurring within the eruption plume and volcanic cloud) and the effects of such a dissolution on the local pH conditions. For all samples, a moderate to sustained Fe release occurred for leaching times comparable with their residence time within the euphotic zone of marine and lacustrine environments (variable from few minutes to few hours), revealing their possible contribution to increase Fe bioavailability.     

Effect of soil-applied calcium carbide and plant derivatives on nitrification inhibition and plant growth promotion

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.     

Seasonal disparity in the co-occurrence of arsenic and fluoride in the aquifers of the Brahmaputra flood plains,Northeast India

Arsenic (As) and fluoride (F^?) in groundwater are increasing global water quality and public health concerns. The present study provides a deeper understanding of the impact of seasonal change on the co-occurrence of As and F^?, as both contaminants vary with climatic patterns. Groundwater samples were collected in pre- and post-monsoon seasons (n = 40 in each season) from the Brahmaputra flood plains (BFP) in northeast India to study the effect of season on As and F^? levels. Weathering is a key hydrogeochemical process in the BFP and both silicate and carbonate weathering are enhanced in the post-monsoon season. The increase in carbonate weathering is linked to an elevation in pH during the post-monsoon season. A Piper diagram revealed that bicarbonate-type water, with Na⁺, K⁺, Ca²⁺, and Mg²⁺ cations, is common in both seasons. Correlation between Cl^? and NO₃ ^? (r = 0.74, p = 0.01) in the post-monsoon indicates mobilization of anthropogenic deposits during the rainy season. As was within the 10 µg L^?1 WHO limit for drinking water and F^? was under the 1.5 mg L^?1 limit. A negative correlation between oxidation reduction potential and groundwater As in both seasons (r = ?0.26 and ?0.49, respectively, for pre-monsoon and post-monsoon, p = 0.05) indicates enhanced As levels due to prevailing reducing conditions. Reductive hydrolysis of Fe (hydr)oxides appears to be the predominant process of As release, consistent with a positive correlation between As and Fe in both seasons (r = 0.75 and 0.73 for pre- and post-monsoon seasons, respectively, at p = 0.01). Principal component analysis and hierarchical cluster analysis revealed grouping of Fe and As in both seasons. F^? and sulfate were also clustered during the pre-monsoon season, which could be due to their similar interactions with Fe (hydr)oxides. Higher As levels in the post-monsoon appears driven by the influx of water into the aquifer, which drives out oxygen and creates a more reducing condition suitable for reductive dissolution of Fe (hydr)oxides. An increase in pH promotes desorption of As oxyanions AsO₄ ^3? (arsenate) and AsO₃ ^3? (arsenite) from Fe (hydr)oxide surfaces. Fluoride appears mainly released from F^?-bearing minerals, but Fe (hydr)oxides can be a secondary source of F^?, as suggested by the positive correlation between As and F^? in the pre-monsoon season.     

Vertical geochemical variations and arsenic mobilization in the shallow alluvial aquifers of the Chapai-Nawabganj District, northwestern Bangladesh: implication of siderite precipitation

Core sediments from three disturbed boreholes (JOR, GHAT, and RAJ) and two undisturbed boreholes (DW1 and DW2) were collected in the study area of the Chapai-Nawabganj district of northwestern Bangladesh for geochemical analyses. In the study area, groundwater samples from fourteen As-contained private wells and five nested piezometers at both the DW1 and DW2 boreholes were also collected and analyzed. The groundwater arsenic concentrations in the uppermost aquifer (10–40 m of depth) range from 3 to 315 μg/L (mean 47.73 ± 73.41 μg/L), while the arsenic content in sediments range from 2 to 14 mg/kg (mean 4.36 ± 3.34 mg/kg). An environmental scanning electron microscope (ESEM) with an energy dispersive X-ray spectrometer was used to investigate the presence of major and trace elements in the sediments. Groundwaters in the study area are generally the Ca–HCO₃ type with high concentrations of As, but low levels of Fe, Mn, NO₃ ^? and SO ₄ ^?2 . The concentrations of As, Fe, Mn decrease with depth in the groundwater, showing vertical geochemical variations in the study area. Statistical analysis clearly shows that As is closely associated with Fe and Mn in the sediments of the JOR core (r = 0.87, p < 0.05 for Fe and r = 0.78, p < 0.05 for Mn) and GHAT core (r = 0.95, p < 0.05 for Fe and r = 0.93, p < 0.05 for Mn), while As is not correlated with Fe and Mn in groundwater. The comparatively low Fe and Mn concentrations in some groundwater and the ESEM image revealed that siderite precipitated as a secondary mineral on the surface of the sediment particles. The correlations along with results of sequential extraction experiments indicated that reductive dissolution of FeOOH and MnOOH represents a mechanism for releasing arsenic into the groundwater.     

Aerosol-trace gases interactions and their role in air quality control of Delhi city (India)

Atmospheric dust is considered to be the major cause of poor air quality due to its contribution to high particulate levels, but their interaction with the acidic gases helps in controlling the level of SO₂ and NO₂ through ambient neutralization reactions. In the present study, the interaction of acidic gases such as SO₂ and NO₂ with alkaline dust was investigated during October, 2013–July, 2014 at a site named as Babarpur located at the Trans-Yamuna region of Delhi. The concentration of SO₂ ranged from 10 to 170 μg/m³ with an average of 36 μg/m³ while that of NO₂ ranged from 15 to 54 μg/m³ with an average of 26?±?8 μg/m³. The results were observed to be well within the National Ambient Air Quality Standard (NAAQS) limits prescribed by the Central Pollution Control Board (CPCB). The average concentrations of SO₂ during day and night time were recorded as 31?±?18 and 43?±?53 μg/m³ respectively while the mean concentrations of NO₂ during day and night time were recorded as 26?±?7 and 27?±?12 μg/m³ respectively. A positive correlation between SO₄^2? and NO₃^? was also observed indicating their secondary aerosol formation. In aerosol phase, average concentrations of SO₄^2? during day and night time were 3.9?±?0.3 and 6.5?±?2.3 μg/m³ respectively while that of NO₃^? were 9.5?±?1.5 and 7.3?±?0.5 μg/m³ respectively. Molar ratios of Ca²⁺/SO₄^2?, NH₄⁺/SO₄^2?, and NH₄⁺/NO₃^? were observed as 8, 5, and 1.7 during daytime and 1.5, 0.4, and 0.8 during nighttime respectively. Such molar ratios confirmed high concentrations of sulphate (SO₄)^2? and low concentrations of nitrate (NO₃^?) during night time, thereby indicating different pathway of aerosol formation during day and night time. Surface morphology and elemental composition of aerosol samples showed various oval, globular, and platy shapes where the diameter varied from few nm to ~5 μm depending on their precursors. There were certain shapes like grossularite, irregular aggregate, grape-like, triangular, and flattened which indicate the crustal origin of aerosols and their possible role in SO₂ and NO₂ adsorption.     

The Role of One- and Two-Electron Transfer Reactions in Forming Thermodynamically Unstable Intermediates as Barriers in Multi-Electron Redox Reactions

In the aquatic geochemical literature, a redox half-reaction is normally written for a multi-electron process (n > 2); e.g., sulfide oxidation to sulfate. When coupling two multi-electron half-reactions, thermodynamic calculations indicate possible reactivity, and the coupled half-reactions are considered favorable even when there is a known barrier to reactivity. Thermodynamic calculations should be done for one or two-electron transfer steps and then compared with known reactivity to determine the rate controlling step in a reaction pathway. Here, thermodynamic calculations are presented for selected reactions for compounds of C, O, N, S, Fe, Mn and Cu. Calculations predict reactivity barriers and agree with one previous analysis showing the first step in reducing O₂ to O₂ ^? with Fe²⁺ and Mn²⁺ is rate limiting. Similar problems occur for the first electron transfer step in these metals reducing NO₃ ^?, but if reactive oxygen species form or if two-electron transfer steps with O atom transfer occur, reactivity becomes favorable. H₂S and NH₄ ⁺ oxidation in a one-electron transfer step by O₂ is also not favorable unless activation of oxygen can occur. H₂S oxidation by Cu²⁺, Fe(III) and Mn(III, IV) phases in two-electron transfer steps is favorable but not in one-electron steps indicating that (nano)particles with bands of orbitals are needed to accept two electrons from H₂S. NH₄ ⁺ oxidation by Fe(III) and Mn(III, IV) phases is generally not favorable for both one- and two-electron transfer steps, but their reaction with hydroxylamine and hydrazine to form N₂O and N₂, respectively, is favorable. The anammox reaction using hydroxylamine via nitrite reduction is the most favorable for NH₄ ⁺ oxidation. Other chemical processes including photosynthesis and chemosynthesis are considered for these element–element transformations.     

Evaluation of groundwater quality and health risks from contamination in the north edge of the Loess Plateau,Yulin City,Northwest China

Groundwater is a vital source for domestic and irrigation purposes in the loess area of Northwest China where climate is arid. However, the quality of groundwater in this area is deteriorating due to intensive industrial and agricultural activities, and this has a great adverse impact on human health. In order to better understand the pollution status of groundwater and the health risks to local residents, comprehensive water quality index was applied to assess the quality of drinking water in Yulin City, Northwest China, and sodium adsorption ratio, sodium percentage, residual sodium carbonate and permeability index were used to evaluate the quality of irrigation water. Moreover, the health risks caused by ingestion of groundwater were evaluated using the model proposed by the Ministry of Environmental Protection of the PR China. The results show that all groundwater samples for irrigation will not induce soil salinization, but more than half of them are not suitable for drinking, and Fe, Mn, TH, Mg²⁺ and NO₃–N are the common contaminants which are mainly from natural processes, industrial and agricultural activities. The health risk assessment indicates that children face greater non-carcinogenic risk than adults. The order of contribution of contaminants to non-carcinogenic risk is NO₃ ^? > As > F^? > Fe > Mn > Ba²⁺ > Cr⁶⁺ > Zn > NO₂ ^?. The average carcinogenic risk of carcinogens (Cr⁶⁺ and As) is 1.17 × 10^?4 and 1.37 × 10^?4 for adults and children, respectively, which surpasses the permissible level (1 × 10^?6) stipulated by the Ministry of Environmental Protection of the PR China. Hence, effective measures are highly demanded to manage groundwater pollution and reduce the risks to human health.     

Detection of tyrosine,trace metals and nutrients in cow dung: the environmental significance in soil and water environments

This study examined the dissolved organic matter (DOM) components of cow dung using a combination of fluorescence (excitation–emission matrix, EEM) spectroscopy and parallel factor (PARAFAC) modelling along with eleven trace metals using ICP-MS and nutrients (NH₄⁺ and NO₃^?) using an AA3 auto analyser. EEM–PARAFAC analysis demonstrated that cow dung predominantly contained only one fluorescent DOM component with two fluorescence peaks (Ex/Em = 275/311 nm and Ex/Em = 220/311 nm), which could be denoted as tyrosine by comparison with its standard. Occurrence of tyrosine can be further confirmed by the FTIR spectra. Trace metals analysis revealed that Na, K and Mg were significantly higher than Ca, Fe, Mn, Zn Sr, Cu, Ni and Co. The NH₄⁺ concentrations were substantially higher than NO₃^?. These results thus indicate that the dissolved components of the cow dung could be useful for better understanding its future uses in various important purposes.     

The impact of nitrogenous and phosphorous nutrients from selected point sources in Kisumu City on River Kisat and Nyalenda Wigwa Stream before their discharge into Winam Gulf,Lake Victoria

Various industrial facilities including a fish-processing factory, a matchbox factory, a flour mill and a landfill, all in Kisumu City in Kenya, were studied and found to discharge significant amounts of NO₂ ^?–N, NO₃ ^?–N, org N, total N and total P into River Kisat and Winam Gulf of Lake Victoria, with  % increases in the mean levels at the outlets of these facilities ranging from 9.6 to 200, 5.9 to 43.5, 9.3 to 96.1, 8.1 to 35.5 and 9.7 to 50.5 %, respectively. The concentrations of NO₂ ^?–N, NO₃ ^?–N, NH₃–N, org N and total N attributable to these facilities increased by 1,509, 51.1, 112.6, 97.5 and 90.6 %, respectively, at the point of entry into Rive Kisat. The Nyalenda Wastewater Stabilization Ponds reduced the mean levels of NO₂ ^?–N, NO₃ ^?–N, org N, total N and T-P by 50, 10.4, 16.6, 7.8 and 30.8 %, respectively, indicating low efficacy of their removal and potential impact on water quality in Lake Victoria. The efficacy of the Kisat wastewater treatment plant was also found to be very low with  % reductions of the analysed nutrients ranging from 2.82 to 41.30 %.     

Rates of Biotite Weathering,and Clay Mineral Transformation and Neoformation,Determined from Watershed Geochemical Mass-Balance Methods for the Coweeta Hydrologic Laboratory,Southern Blue Ridge Mountains,North Carolina,USA

Biotite is a common constituent of silicate bedrock. Its weathering releases plant nutrients and consumes atmospheric CO₂. Because of its stoichiometric relationship with its transformational weathering product and sensitivity to botanical activity, calculating biotite weathering rates using watershed mass-balance methods has proven challenging. At Coweeta Hydrologic Laboratory the coupling of biotite to its transformational weathering product is only valid if the stoichiometric relationship for the two phases is known; this relationship is unlikely layer-for-layer. Rates of biotite weathering and transformation of its secondary weathering product at the Coweeta Hydrological Laboratory are comparable with other Appalachian watersheds. The magnitude and sign of the difference between field- and laboratory-determined biotite weathering rates are similar to those of other silicate minerals. The influence of major-cation proportions in biomass on the rates of biotite weathering and transformational weathering product is greatest for watersheds with high biomass aggradation rates. The watershed with the lowest bedrock reactivity and highest flushing rate yielded the highest gibbsite formation rate of ~500 mol ha^?1 year^?1 and lowest kaolin-group mineral formation rates of 4–78 mol ha^?1 year^?1. The kaolin-group mineral formation rate increases as bedrock reactivity increases and flushing rate decreases to a maximum of ~300 mol ha^?1 year^?1, with a similar minimum gibbsite formation rate. The relative differences in bedrock reactivity and flux of water through Coweeta Hydrological Laboratory watersheds studied appear to be invariant over geologic timescales.     

Mass-size distribution of PM10 and its characterization of ionic species in fine (PM2.5) and coarse (PM10−2.5) mode, New Delhi, India

Size distribution of PM₁₀ mass aerosols and its ionic characteristics were studied for 2 years from January 2006 to December 2007 at central Delhi by employing an 8-stage Andersen Cascade Impactor sampler. The mass of fine (PM_2.5) and coarse (PM_10?2.5) mode particles were integrated from particle mass determined in different stages. Average concentrations of mass PM₁₀ and PM_2.5 were observed to be 306 ± 182 and 136 ± 84 μg m^?3, respectively, which are far in excess of annual averages stipulated by the Indian National Ambient Air Quality Standards (PM₁₀: 60 μg m^?3 and PM_2.5: 40 μg m^?3). The highest concentrations of PM_10?2.5 (coarse) and PM_2.5 (fine) were observed 505 ± 44 and 368 ± 61 μg m^?3, respectively, during summer (June 2006) period, whereas the lower concentrations of PM_10?2.5 (35 ± 9 μg m^?3) and PM_2.5 (29 ± 13 μg m^?3) were observed during monsoon (September 2007). In summer, because of frequent dust storms, coarse particles are more dominant than fine particles during study period. However, during winter, the PM_2.5 contribution became more pronounced as compared to summer probably due to enhanced emissions from anthropogenic activities, burning of biofuels/biomass and other human activities. A high ratio (0.58) of PM_2.5/PM₁₀ was observed during winter and low (0.24) during monsoon. A strong correlation between PM₁₀ and PM_2.5 (r ² = 0.93) was observed, indicating that variation in PM₁₀ mass is governed by the variation in PM_2.5. Major cations (NH₄ ⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺) and anions (F^?, Cl^?, SO₄ ^2? and NO₃ ^?) were analyzed along with pH. Average concentrations of SO₄ ^2? and NO₃ ^? were observed to be 12.93 ± 0.98 and 10.33 ± 1.10 μg m^?3, respectively. Significant correlation between SO₄ ^2? and NO₃ ^? in PM_1.0 was observed indicating the major sources of secondary aerosol which may be from thermal power plants located in the southeast and incomplete combustion by vehicular exhaust. A good correlation among secondary species (NH⁺, NO₃ ^? and SO₄ ^2?) suggests that most of NH₄ ⁺ is in the form of ammonium sulfate and ammonium nitrate in the atmosphere. During winter, the concentration of Ca²⁺ was also higher; it may be due to entrainment of roadside dust particles, traffic activities and low temperature. The molar ratio (1.39) between Cl^? and Na⁺ was observed to be close to that of seawater (1.16). The presence of higher Cl^? during winter is due to western disturbances and probably local emission of Cl^? due to fabric bleaching activity in a number of export garment factories in the proximity of the sampling site.     

Spatial Distribution of Nitrous Oxide (N<Subscript>2</Subscript>O) in the Reloncaví Estuary–Sound and Adjacent Sea (41°–43° S), Chilean Patagonia

Fjords and estuaries exchange large amounts of solutes, gases, and particulates between fluvial and marine systems. These exchanges and their relative distributions of compounds/particles are partially controlled by stratification and water circulation. The spatial and vertical distributions of N₂O, an important greenhouse gas, along with other oceanographic variables, are analyzed from the Reloncaví estuary (RE) (~41° 30′ S) to the gulf of Corcovado in the interior sea of Chiloé (43° 45′ S) during the austral winter. Freshwater runoff into the estuary regulated salinity and stratification of the water column, clearly demarking the surface (<5 m depth) and subsurface layer (>5 m depth) and also separating estuarine and marine influenced areas. N₂O levels varied between 8.3 and 21 nM (corresponding to 80 and 170 % saturation, respectively), being significantly lower (11.8 ± 1.70) at the surface than in subsurface waters in the Reloncaví estuary (14.5 ± 1.73). Low salinity and NO₃ ^?, NO₂ ^?, and PO₄ ^3? levels, as well as high Si(OH)₄ values were associated with low surface N₂O levels. Remarkably, an accumulation of N₂O was observed in the subsurface waters of the Reloncaví sound, associated with a relatively high consumption of O₂. The sound is exposed to increasing anthropogenic impacts from aquaculture and urban discharge, occurring simultaneously with an internal recirculation, which leads to potential signals of early eutrophication. In contrast, within the interior sea of Chiloé (ISC), most of water column was quasi homohaline and occupied by modified subantarctic water (MSAAW), which was relatively rich in N₂O (12.6 ± 2.36 nM) and NO₃ ^? (18.3 ± 1.63 μM). The relationship between salinity, nutrients, and N₂O revealed that water from the open ocean, entering into ISC (the Gulf of Corcovado) through the Guafo mouth, was the main source of N₂O (up to 21 nM), as it gradually mixed with estuarine water. In addition, significant relationships between N₂O excess vs. AOU and N₂O excess vs. NO₃ ^? suggest that part of N₂O is also produced by nitrification. Our results show that the estuarine and marine waters can act as light source or sink of N₂O to the atmosphere (air–sea N₂O fluxes ranged from ?1.57 to 5.75 μmol m^?2 day^?1), respectively; influxes seem to be associated to brackish water depleted in N₂O that also caused a strong stratification, creating a barrier to gas exchange.     

Geochemical evaluation of nitrate and fluoride contamination in varied hydrogeological environs of Prakasam district,southern India

Hydrogeochemical controlling factors for high rate of groundwater contamination in stressed aquifer of fractured, consolidated rocks belonging to semi-arid watershed are examined. The groundwater in mid-eastern part of Prakasam district confining to Musi-Gundlakamma sub-basins is heavily contaminated with nitrate and fluoride. Distinct water chemistry is noticed among each group of samples segregated based on concentration of these contaminants. The nitrate is as high as 594 mg/l and 57 % of the samples have it in toxic level as per BIS drinking water standards, so also the fluoride which has reached a maximum of 8.96 mq/l and 43 % of samples are not fit for human consumption. Nitrate contamination is high in shallow aquifers and granitic terrains, whereas fluoride is in excess concentration in deeper zones and meta-sediments among the tested wells, and 25 % of samples suffer from both NO₃ ^? and F^? contamination. Na⁺ among cations and HCO₃ ^? among anions are the dominant species followed by Mg²⁺ and Cl^?. The NO₃ ^?-rich groundwater is of Ca²⁺–Mg²⁺–HCO₃ ^?, Ca²⁺–Mg²⁺–Cl^? and Na⁺–HCO₃ ^? type. The F^?-rich groundwater is dominantly of Na⁺–HCO₃ ^? type and few are of Na⁺–SO₄ ^2? type, whereas the safe waters (without any contaminants) are of Ca²⁺–Mg²⁺–HCO₃ ^?– and Na⁺–HCO₃ ^? types. High molecular percentage of Na⁺, Cl^?, SO₄ ^2? and K^? in NO₃ ^? rich groundwater indicates simultaneous contribution of many elements through domestic sewerage and agriculture activity. It is further confirmed by analogous ratios of commonly associated ions viz NO₃ ^?:Cl^?:SO₄ ^2? and NO₃ ^?:K⁺:Cl^? which are 22:56:22 and 42:10:48, respectively. The F^? rich groundwater is unique by having higher content of Na⁺ (183 %) and HCO₃ ^? (28 %) than safe waters. The K⁺:F^?:Ca²⁺ ratio of 10:5:85 and K⁺:F^?: SO₄ ^2? of 16:7:77 support lithological origin of F^? facilitated by precipitation of CaCO₃ which removes Ca²⁺ from solution. The high concentrations of Na⁺, CO₃ ^? and HCO₃ ^? in these waters act as catalyst allowing more fluorite to dissolve into the groundwater. The indices, ratios and scatter plots indicate that the NO₃ ^? rich groundwater has evolved through silicate weathering-anthropogenic activity-evapotranspiration processes, whereas F^? rich groundwater attained its unique chemistry from mineral dissolution-water–rock interaction-ion exchange. Both the waters are subjected to external infusion of certain elements such as Na⁺, Cl^?, NO₃ ^? which are further aggravated by evaporation processes leading to heavy accumulation of contaminants by raising the water density. Presence of NO₃ ^? rich samples within F^? rich groundwater Group and vice versa authenticates the proposed evolution processes.     

Antimony adsorption on kaolinite in the presence of competitive anions

Antimony (Sb) emissions to the environment are increasing, and there is a dearth of knowledge regarding Sb fate and behavior in natural systems. In natural systems, the presence of competitive anions may compete with Sb for adsorption sites on mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of Sb(III) on kaolinite was investigated in the presence of competitive anions. Kinetic studies suggest that adsorption reaction of Sb(III) on kaolinite is rapid initially and becoming slow after 12 h both in binary Sb(III)–kaolinite system and in ternary Sb(III)-competitive anion–kaolinite system. The presence of PO₄ ^3? has a much stronger and more obvious promotive effect on the adsorption of Sb(III) on kaolinite compared with the other two anions. The adsorption data of Sb(III) on kaolinite in the absence and presence of competitive anions at three temperatures were successfully modeled using Langmuir (r ² > 0.95) and Freundlich (r ² > 0.95) isotherms. Accompanied the adsorption of Sb(III) on kaolinite, significant oxidation of Sb(III) to Sb(V) had occurred under the experimental conditions used in this study. The presence of kaolinite which has a larger specific surface area could increase the contact area between the adsorbed Sb(III) and oxygen in the bulk solution, which promoted the oxidation rate of Sb(III) to Sb(V).     

Hydrogeological processes controlling the release of arsenic in parts of 24 Parganas district,West Bengal

A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ > Fe²⁺ for cations and HCO₃ ^? > PO₄ ^3? > Cl^? > SO₄ ^2? > NO₃ ^? for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO₃ type. Based on conventional graphical plots for (Ca + Mg) vs. (SO₄ + HCO₃) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas.     

Effect of heavy metal and alkali contamination on the swelling properties of kaolinite

One of the most important factors that determine engineering properties of soils are the type and the amount of clay present in soil. Kaolinite being a very common and non-swelling clay mineral in soil was chosen as the medium, and significance of the change in swelling property of kaolinite due to contaminant-clay interaction was investigated. The amount of change in swelling percentages of the kaolinite due to contamination with 10,000 ppm solutions of Pb(NO₃)₂ and Zn(NO₃)₂ was determined using oedometers. For uncontaminated kaolinite, the amount of swell was determined as 2.2%. For Pb-contaminated and Zn-contaminated kaolinite, these values reached to 5.8 and 5.3%, respectively. Besides heavy metals, kaolinite was also contaminated with 4 N NaOH. The biggest change in the amount of swelling was obtained from NaOH-contaminated kaolinite which is 13.9%. In addition to swelling percentages, swelling pressures were also determined. The swelling pressure of the uncontaminated kaolinite was found as 1.06 N/cm². For Zn and Pb-contaminated kaolinite, this value reached up to 2.0 and 2.6 N/cm². The NaOH-contaminated kaolinite has the greatest swelling pressure which was 230 N/cm².