Preparation of calcium oxalate—bromopyrogallol red inclusion sorbent and application to treatment of cationic dye and heavy metal wastewaters

Background, aim, and scope  Dye pollutants are a major class of environmental contaminants. Over 100,000 dyes have been synthesized worldwide and more than 700,000 tons are produced annually and over 5% are discharged into aquatic environments. The adsorption or sorption is one of the most efficient methods to remove dye and heavy metal pollutants from wastewater. However, most of the present sorbents often bear some disadvantages, e.g. low sorption capacity, difficult separation of spoil, complex reproduction, or secondary pollution. Development of novel sorbents that can overcome these limitations is desirable. Materials and methods  On the basis of the chemical coprecipitation of calcium oxalate (CaC₂O₄), bromopyrogallol red (BPR) was embedded during the growing of CaC₂O₄ particles. The ternary C₂O₄ ^2––BPR–Ca²⁺ sorbent was yielded by the centrifugation. Its composition was determined by spectrophotometry and AAS, and its structure and morphology were characterized by powder X-ray diffraction (XRD), laser particle-size analysis, and scanning electron microscopy (SEM). The adsorption of ethyl violet (EV) and heavy metals, e.g. Cu(II), Cd(II), Ni(II), Zn(II), and Pb(II) were carried out and their removal rate determined by spectrophotometry and ICP-OES. The adsorption performance of the sorbent was compared with powder activated carbon. The Langmuir isothermal model was applied to fit the embedment of BPR and adsorption of EV. Results  The saturation number of BPR binding to CaC₂O₄ reached 0.0105 mol/mol and the adsorption constant of the complex was 4.70 × 10⁵ M^–1. Over 80% of the sorbent particles are between 0.7 and 1.02 μm, formed by the aggregation of the global CaC₂O₄/BPR inclusion grains of 30–50 nm size. Such a material was found to adsorb cationic dyes selectively and sensitively. Ethyl violet (EV) was used to investigate the adsorption mechanism of the material. One BPR molecule may just bind with one EV molecule. The CaC₂O₄/BPR inclusion material adsorbed EV over two times more efficiently than the activated carbon. The adsorption of EV on the CaC₂O₄/BPR inclusion sorbent was complete in only 5 min and the sedimentation complete in 1 h. However, those of EV onto activated carbon took more than 1.5 and 5 h, respectively. The treatment of methylene blue and malachite green dye wastewaters indicated that only 0.4% of the sorbent adsorbed over 80% of color substances. Besides, the material can also adsorb heavy metals by complexation with BPR. Over 90% of Pb²⁺, and approximately 50% of Cd²⁺ and Cu²⁺, were removed in a high Zn²⁺-electroplating wastewater when 3% of the material was added. Eighty-six percent of Cu²⁺, and 60% of Ni²⁺ and Cd²⁺, were removed in a high Cd²⁺-electroplating wastewater. Discussion  The embedment of BPR into CaC₂O₄ particles responded to the Langmuir isothermal adsorption. As the affinity ligand of Ca²⁺, BPR with sulfonic groups may be adsorbed into the temporary electric double layer during the growing of CaC₂O₄ particles. Immediately, C₂O₄ ^2– captured the Ca²⁺ to form the CaC₂O₄ outer enclosed sphere. Thus, BPR may be released and embedded as a sandwich between CaC₂O₄ layers. The adsorption of EV on the sorbent obeyed the Langmuir isothermal equation and adsorption is mainly due to the ion-pair attraction between EV and BPR. Different from the inclusion sorbent, the activated carbon depended on the specific surface area to adsorb organic substances. Therefore, the adsorption capacity, equilibrium, and sedimentation time of the sorbent are much better than activated carbon. The interaction of heavy metals with the inclusion sorbent responded to their coordination. Conclusions  By characterizing the C₂O₄ ^2––BPR–Ca²⁺ inclusion material using various modern instruments, the ternary in situ embedment particle, [(CaC₂O₄)₉₅(BPR)] _n ^2n–, an electronegative, micron-sized adsorbent was synthesized. It is selective, rapid, and highly effective for adsorbing cationic dyes and heavy metals. Moreover, the adsorption is hardly subject to the impact of electrolytes. Recommendations and perspectives  The present work provides a simple and valuable method for preparing the highly effective adsorbent. If a concentrated BPR wastewater was reused as the inclusion reactant, the sorbent will be low cost. By selecting the inclusion ligand with a special structure, we may prepare some particular functional materials to recover the valuable substances from seriously polluted wastewaters. The recommended method will play a significant role in development of advanced adsorption materials. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Deposition processes of ionic constituents to snow cover

Atmospheric deposition is an important removal process of aerosol particles and gases from the atmosphere. To elucidate the relative contributions of wet and dry processes and in-cloud and below-cloud scavenging based on deposition amounts in winter at Mt. Tateyama, central Japan, we obtained daily samples (December, 2006–March, 2007) of size-segregated aerosol particles and precipitation at Senjyugahara (SJ; 475 m a.s.l.) and vertical samples of spring snow cover at Murododaira (MR, 2450 m a.s.l., 13 km distance from SJ) on the western flank of Mt. Tateyama. The NH₄⁺ and nssSO₄^2? in aerosols were mostly found in the fine fraction (<2 μm), although Na⁺, NO₃^?, and nssCa²⁺ were mainly detected in the coarse fraction (>2 μm). Average ionic concentrations (μg g^?1) in precipitation at SJ were higher about 3.8 for Na⁺ and nssCa²⁺, 3.4 for NO₃^?, 3.7 for NH₄⁺, 2.5 for nssSO₄^2? than those at MR, whereas cumulative precipitation amounts at SJ and MR were, respectively, 84 and 175 cm of water equivalent. Wet and dry deposition amounts during the study period were estimated for sites using size-segregated aerosol data, winter averages of HNO₃, NH₃, and SO₂ concentrations, and dry deposition velocities. Particle-dry deposition comprised about 3% (Na⁺) to 11% (NH₄⁺) of the total deposition at MR. The maximum amounts of gas dry deposition were estimated, respectively, as 4, 13, and 3% of the total deposition at MR for NH₄⁺, NO₃^?, and nssSO₄^2?. The relative contributions of below-cloud scavenging (BCS) between MR and SJ were estimated as considering the wet only deposition amount at MR. Higher contributions of BCS were obtained for Na⁺ (56%) and nssCa²⁺ (45%), whereas BCSs for NH₄⁺, NO₃^?, and nssSO₄^2? were lower than 28%. Ionic constituents existing predominantly in the coarse fraction showed a large contribution of BCS.     

Fenton-like oxidation and mineralization of phenol using synthetic Fe(II)–Fe(III) green rusts

Background, aim, and scope  

In literature, the environmental applications of green rust (GR) have mainly been pointed out through the reduction of inorganic contaminants and the reductive dechlorination of chlorinated organics. However, reactions involving GR for the oxidation and mineralization of organic pollutants remain very scantly described. In this study, the ability of three synthetic Fe(II)–Fe(III) green rusts, GR(CO₃²⁻), GR(SO₄²⁻), and GR(Cl⁻), to promote Fenton-like reaction was examined by employing phenol as a model pollutant. Unlike the traditional Fenton’s reagent (dissolved Fe(II) + H₂O₂), where the pH values have to be lowered to less than 4, the proposed reaction can effectively oxidize the organic molecules at neutral pH and could avoid the initial acidification which may be costly and destructive for the in situ remediation of contaminated groundwater and soils. The green rust reactivity towards the oxidative transformation of phenol was thoroughly evaluated by performing a large kinetic study, chemical analyses, and spectroscopic investigations.     

Chemical characteristics of atmospheric aerosols over southwest coast of India

Ambient aerosol samples, collected from Mangalore region in the southwest coast of India during the period of late winter (February and March) to early summer (April and May), have been analysed for water-soluble ionic species. Their abundance pattern is dominated by HCO₃⁻, SO₄²⁻, Na⁺, Cl⁻, with minor contribution from NO₃⁻, Ca²⁺, NH₄⁺, K⁺ and Mg²⁺ indicating the contribution from not only sea salt, but also from anthropogenic and dust sources; with pronounced seasonal variability. The suspended particulate matter concentration varied from 35 to 160 μg m⁻³, with consistently higher values during the late winter. Back trajectory analysis suggests the origin of the air masses shifting from Indo-Gangetic Plains (during late winter) to those from the Arabian Sea and the area around Persian Gulf during April–May. Air masses passing over Northern India (Indo-Gangetic Plains) impart characteristic contribution of ionic species from fossil fuel combustion, biomass burning and eolian dust as asserted by the factor analysis. A detailed study on characterisation of aerosols from south Asian region is rather sparse but essential for modelling the effect of tropospheric aerosols on climate.     

Gas phase reactions of unsaturated esters with Cl atoms

Background, aim, and scope  

Acrylate and methacrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon (CH₂=CHCOO– and CH₂=CCH₃COO–, respectively) and are widely used in the polymer plastic and resin production. Rate coefficients for Cl reactions for most of the unsaturated esters have not been previously determined, and a good understanding is needed of all the atmospheric oxidation processes of these compounds in order to determine lifetimes in the atmosphere and to evaluate the impact of these reactions on the formation of photo-oxidants and therefore on health and environment.     

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms

Background, aim, and scope  The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF₃CF₂CF₂OCH₃) (1) and its isomer CF₃CF₂CF₂CH₂OH (2). Materials and methods  Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K for reactions of HFE-7000 and CF₃CF₂CF₂CH₂OH, respectively. Results  The measured room temperature rate constants were k(Cl+CF₃CF₂CF₂OCH₃) = (1.24 ± 0.28) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹and k(Cl+CF₃CF₂CF₂CH₂OH) = (8.35 ± 1.63) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k ₁(266–333 K) = (6.1 ± 3.8) × 10⁻¹³exp[−(445 ± 186)/T] cm³ molecule⁻¹ s⁻¹ and k ₂(298–353 K) = (1.9 ± 0.7) × 10⁻¹²exp[−(244 ± 125)/T] cm³ molecule⁻¹ s⁻¹ (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF₃CF₂CF₂OCH₃ and CF₃CF₂CF₂CH₂OH, respectively. Discussion  The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k ₁ and k ₂, HFE-7000 is significantly less reactive than its isomer C₃F₇CH₂OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF₂– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of –CF₂– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C₃H₇CH₂OH, respectively. Conclusions  The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, τ _Cl values as low as 2.5 and 0.4 years for HFE-7000 and C₃H₇CH₂OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF₃CF₂CF₂OCH₃, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. Recommendations and perspectives  The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.     

Recent trends in chemical composition of bulk precipitation at Estonian monitoring stations 1994–2001

Monthly and annual means of main anions (SO₄²⁻, NO₃⁻, Cl⁻) and summed base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺) in bulk precipitation were studied at 10 stations during an 8-year monitoring period. The data showed statistically significant decreasing trends in most cases. Average declines of mean annual volume-weighted concentrations for both anions and cations were about two-fold. Despite the decrease, the loads of S and cations are still relatively high in Estonia (about 4–14 kg S ha⁻¹ and 0.6–1.2 keq ha⁻¹, respectively) compared with the loads in Finland and Sweden. Estimated linear decline trends followed the same pattern as annually combusted oil shale from Estonian power plants and emissions of SO₂ and fly ash. Recent trends in chemical composition of bulk precipitation at the monitoring stations reflected economic changes in Estonia as well as transboundary fluxes from neighbouring countries.     

Seasonal variations of acidic air pollutants in Seoul,South Korea

The annular denuder system (ADS) was used to characterize seasonal variations of acidic air pollutants in Seoul, South Korea. Fifty- four 24 h samples were collected over four seasons from October 1996 to September 1997. The annual mean concentrations of HNO₃, HNO₂, SO₂ and NH₃ in the gas phase were 1.09, 4.51, 17.3 and 4.34 μg m^-3, respectively. The annual mean concentrations of PM_2.5(d_p≤2.5 μm in aerodynamic diameter, 50% cutoff), SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were 56.9, 8.70, 5.97 and 4.19 μg m^-3, respectively. All chemical species monitored from this study showed statistical seasonal variations. Nitric acid (HNO₃) and ammonia (NH₃) exhibited substantially higher concentrations during the summer, while nitrous acid (HNO₂) and sulfur dioxide(SO₂) were higher during the winter. Concentrations of PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were higher during the winter months. SO^2-₄, NO^-₃ and NH⁺₄ accounted for 26–38% of PM_2.5. High correlations were found among PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄. The mean H⁺ concentration measured only in the fall was 5.19 nmole m^-3.     

Characterization of PM10 atmospheric aerosol at urban and urban background sites in Fuzhou city, China

Background

PM₁₀ aerosol samples were simultaneously collected at two urban and one urban background sites in Fuzhou city during two sampling campaigns in summer and winter. PM₁₀ mass concentrations and chemical compositions were determined.

Methods

Water-soluble inorganic ions (Cl^?, NO ₃ ^? , SO ₄ ^2? , NH ₄ ⁺ , K⁺, Na⁺, Ca²⁺, and Mg²⁺), carbonaceous species (elemental carbon and organic carbon), and elements (Al, Si, Mg, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, and Pb) were detected using ion chromatography, thermal/optical reflectance, and proton-induced X-ray emission methods, respectively.

Results

PM₁₀ mass concentrations, as well as most of the chemical components, were significantly increased from urban background to urban sites, which were due to enhanced anthropogenic activities in urban areas. Elements, carbonaceous species, and most of the ions were more uniformly distributed at different types of sites in winter, whereas secondary ion SO ₄ ^2? , NO ₃ ^? , and NH ₄ ⁺ showed more evident urban-background contrast in this season. The chemical mass closure indicated that mineral dust, organic matters, and sulfate were the most abundant components in PM₁₀. The sum of individually measured components accounted for 86.9?C97.7% of the total measured PM₁₀ concentration, and the discrepancy was larger in urban area than in urban background area.

Conclusion

According to the principal component analysis?Cmultivariate linear regression model, mineral dust, secondary inorganic ions, sea salt, and motor vehicle were mainly responsible for the PM₁₀ particles in Fuzhou atmosphere, and contributed 19.9%, 53.3%, 21.3%, and 5.5% of PM₁₀, respectively.     

Some results of snow chemical surveys in the Kunnes River valley,East Tienshan mountains,China

Chemical surveys of snow were carried out in the upper reaches of the Kunnes River, a tributary of the Yili River in East Tienshan Mountains, China. Some surprisingly high values of sodium and potassium (K⁺+Na⁺) ranging from 4.44 to 8.99 mg/l compared with other data from neighboring areas are detected. Moreover, some relative high values of SO₄²⁻ with mean concentration 15.8 mg/l for new snow and 14.40 mg/l for deposited snow, ranging from 10.43 to 23.71 mg/l are also found. Therefore, it is inferred that the sodium and potassium (K⁺+Na⁺) are in the forms of sulfate and that the sources of the sulfate are deserts and some dried lakes in Central Asia. It is also found that there is obviously spatial variation of ions such as K⁺+Na⁺, Ca²⁺, SO₄²⁻ and HCO₃⁻. The concentrations of K⁺+Na⁺ and SO₄²⁻, and that of Ca²⁺ and HCO₃⁻ have similar spatial pattern. The temporal pattern of ion concentration of new snow is considered to be mainly controlled by the depth and area of snow cover in the study area and in the areas to the west.     

Quantitative chemical composition and characteristics of aerosols over western India: One-year record of temporal variability

One-year quantitative chemical data set consisting of water-soluble constituents (NH₄⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^?, NO₃^?, SO₄^2? and HCO₃^?), crustal and trace elements (Al, Fe, Ca, Mg, K, Mn, Zn, Pb) and carbonaceous species (OC, EC) in ambient aerosols, collected over an urban site located in a high-dust semi-arid region of western India, reveals excellent linear relationship (r² = 0.92; slope = 0.96 ± 0.05) between gravimetrically assessed TSP (total suspended particulates) and chemically analyzed aerosol mass. The TSP abundance ranging from 60 to 250 μg m^?3, over a period of 12 months (January–December), is dominated by mineral dust (～70%); whereas contribution from sea-salts, anthropogenic and carbonaceous species exhibits significant temporal variability depending upon the wind regimes. The mineral dust is enriched in Ca, Mg and Fe with respect to upper continental crust (UCC); whereas Zn and Pb exhibit a characteristic anthropogenic source and high enrichment factors. The carbonaceous species show significant seasonality; with dominance of OC (range: 4.6–28 μg m^?3; average: 12.8 μg m^?3; SD: 6.8) and minor contribution from EC (range: 0.3–4.4 μg m^?3; average: 2.4 μg m^?3; SD: 1.4). The observed concentrations are significantly lower than those reported for the metro cities in South Asia but the OC/EC ratios (range: 4.3–35; average: 8.3; SD: 5.7) are significantly higher than the characteristic ratio (～2–4) reported for the urban atmosphere. Such quantitative chemical characterization of aerosols is essential in assessing their role in atmospheric chemistry and climate change. This study could also be useful in understanding the physical and optical aerosol properties documented from the same site and thus, in validating regional climate models.     

Two extreme types of mixing of dust with urban aerosols observed in Kosa particles: ‘After’ mixing and ‘on-the-way’ mixing

Besides well-known episodic Kosa during spring, high concentrations of Ca²⁺ in aerosols were observed early in summer as well as in the semi-continuous data of the aerosols at the summit of Mt. Fuji. We further analysed the data to study the chemical characteristics of the high calcium event during early summer. The back trajectory analyses of the event indicated that Ca was transported from arid and semi-arid regions (e.g. the Taklamakan desert) through the westerly-dominated troposphere higher than the height of the summit of Fuji. The amount of SO₄^2? was always equivalent to that of NH₄⁺ unlike the case of the normal Kosa period where SO₄^2? is in excess with respect to NH₄⁺. This shows the ‘after’ mixing of unreacted CaCO₃ of Kosa origin with (NH₄)₂SO₄, which was only realized by the downward injection of Kosa particles from higher altitudes to the air masses of different origin. In the case of normal Kosa, the air bearing Kosa particles passed through the polluted area to absorb unneutralized acids (‘on-the-way’ mixing), whereas in the case of the Kosa-like phenomena in summer, the acids from the polluted area have been neutralized by NH₄⁺ and become inactive before mixing with CaCO₃ (“after” mixing). We have simplified the chemistry of aerosols using their three major components, Ca²⁺, SO₄^2? and NH₄⁺, and introduced a new triangle diagram with the three assumed end-members of CaCO₃, CaSO₄ and (NH₄)₂SO₄ to quantify the contribution of the ‘after’ mixing to the aerosols (AMI; ‘after’ mixing index). Based on the back trajectories of some high AMI cases, CaCO₃ in Kosa particles was transported through the middle troposphere (5000–7000 m) and descended to meet another air mass where SO₄^2? had been already neutralized by NH₃.     

Sampling and chemical analysis of ice crystals as a function of size

Size-classified ice crystal samples were collected during the Spring of 1998, at the Jungfraujoch High-Alpine Research Station (3454 m), located in Switzerland. A procedure modified from the Guttalgor method, originally developed for size-selective sampling of raindrops by Bächmann et al. (Atmos. Environ. 26A (1992) 1795) was used to sample ice crystals during precipitation events. The size-classified ice crystal samples were analyzed using ion chromatography to determine the concentrations of Na⁺, NH₄⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃⁻, and SO₄²⁻ in each size class. For ions associated with coarse mode aerosol, Na⁺, K⁺, Ca²⁺, Mg²⁺, and Cl⁻, concentration increased with decreasing ice crystal size, suggesting scavenging by nucleation. For the remaining ions, mixed behavior was observed suggesting a combination of gas phase scavenging and scavenging via riming.     

Atmospheric deposition and canopy exchange processes in alpine forest ecosystems (northern Italy)

Throughfall and bulk precipitation chemistry were studied for five years (June 1994–May 1999) at two high elevation forest sites (Val Gerola and Val Masino) which were known to differ in terms of tree health, as assessed by live crown condition. The ion concentration of bulk precipitation samples did not differ significantly between sites, except for Mg²⁺, while the throughfall concentrations differed in the measured values of H⁺, N-NO₃⁻, Cl⁻, Na⁺, K⁺, DOC and weak organic acids. The results of the application of the canopy exchange model indicated a higher contribution from the dry deposition of N-NO₃⁻, N-NH₄⁺ and H⁺ at Val Gerola, where the damage symptoms were more evident. In addition, the canopy leaching of Ca²⁺, K⁺ and weak organic acids were 47%, 21% and 27% higher at Val Gerola than at Val Masino. Annual SO₄²⁻ deposition fluxes (21.3 kg ha⁻¹ yr⁻¹ at Val Masino and 23.6 kg ha⁻¹ yr⁻¹ at Val Gerola) were similar to those reported for moderately polluted European and U.S. sites. Annual N loads were 13.6 and 13.1 kg ha⁻¹ yr⁻¹ in the bulk input, and 15.0 and 18.0 kg ha⁻¹ yr⁻¹ in throughfall inputs, at Val Masino and Val Gerola, respectively. The contribution of the organic fraction to the total N atmospheric deposition load is significant, constituting 17% of the bulk flux and 40% of the throughfall flux. Measured nitrogen loads exceed the critical nutrient loads by several kg N ha⁻¹ at both stations. In particular the nitrogen throughfall load at Val Gerola was about 3 times higher than the critical values.     

Chemical and strontium isotope characterization of rainwater in karst virgin forest,Southwest China

Strontium isotope ratios and concentrations of Ca²⁺, NH₄⁺, Na⁺, K⁺, Mg²⁺, Cl^?, SO₄^2?, NO₃^? and Al³⁺, Sr²⁺ were measured for 52 rainwater samples collected in virgin forest in a rural region between May 2007 and Dec. 2008. The rainwater pH values vary from 4.1 to 7.2 with a volume weight mean (VWM) value of 5.40. 40 of 52 samples have pH value above 5.0, indicating that the regional rainwater was not acidic. Among anions and cations, sulphate concentration (40.4 μeq l^?1, VWM) is the highest in the rainwater, followed by ammonium and calcium (30.2 and 20.8 μeq l^?1, VWM). Rainwater quality is characterized by low salinity and neutralized pH.The chemical compositions and ⁸⁷Sr/⁸⁶Sr ratios of the rainwater samples vary considerably. Using Na⁺ concentration as an indicator of marine origin, the proportions of sea salt and crustal elements were estimated from elemental ratios. The ⁸⁷Sr/⁸⁶Sr ratios were used to characterize different sources base on the data sets of this study and those from literatures. Such sources include weathering of limestone (⁸⁷Sr/⁸⁶Sr = 0.7075), remote soil dust (⁸⁷Sr/⁸⁶Sr > 0.7135) and anthropogenic source (fertilizers: ⁸⁷Sr/⁸⁶Sr = 0.7079). The results of the present study suggest that one likely source for high ammonium and calcium concentration is local soil. Due to a large contribution of these cations to the sulphate neutralization action, the rainwater in this region displays non-acidity, and thus has not significant environmental impact. The wet precipitation in the karst virgin forest in Guizhou province is strongly influenced by natural sources rather than anthropogenic sources.     

Effect of Pb toxicity on leaf growth, antioxidant enzyme activities, and photosynthesis in cuttings and seedlings of Jatropha curcas L

Background  

Cuttings and seedlings of Jatropha curcas L. were exposed to different regimes of lead (Pb) stress as Pb(NO₃)₂ at 0 (CK), 0.5, 1, 2, 3, and 4 mM kg⁻¹ soil.     

Natural and anthropogenic factors affecting the groundwater quality in the Nandong karst underground river system in Yunan, China

The Nandong Underground River System (NURS) is located in a typical karst agriculture dominated area in the southeast Yunnan Province, China. Groundwater plays an important role for social and economical development in the area. However, with the rapid increase in population and expansion of farm land, groundwater quality has degraded. 42 groundwater samples collected from springs in the NURS showed great variation of chemical compositions across the study basin. With increased anthropogenic contamination in the area, the groundwater chemistry has changed from the typical Ca–HCO₃ or Ca (Mg)–HCO₃ type in karst groundwater to the Ca–Cl (+ NO₃) or Ca (Mg)–Cl (+ NO₃), and Ca–Cl (+ NO₃ + SO₄) or Ca (Mg)–Cl (+ NO₃ + SO₄) type, indicating increases in NO₃⁻, Cl⁻ and SO₄²⁻ concentrations that were caused most likely by human activities in the region. This study implemented the R-mode factor analysis to investigate the chemical characteristics of groundwater and to distinguish the natural and anthropogenic processes affecting groundwater quality in the system. The R-mode factor analysis together with geology and land uses revealed that: (a) contamination from human activities such as sewage effluents and agricultural fertilizers; (b) water–rock interaction in the limestone-dominated system; and (c) water–rock interaction in the dolomite-dominated system were the three major factors contributing to groundwater quality. Natural dissolution of carbonate rock (water–rock interaction) was the primary source of Ca²⁺ and HCO₃⁻ in groundwater, water–rock interaction in dolomite-dominated system resulted in higher Mg²⁺ in the groundwater, and human activities were likely others sources. Sewage effluents and fertilizers could be the main contributor of Cl⁻, NO₃⁻, SO₄²⁻, Na⁺ and K⁺ to the groundwater system in the area. This study suggested that both natural and anthropogenic processes contributed to chemical composition of groundwater in the NURS, human activities played the most important role, however.     

NH4+, NO3−, and SO42− in roadside and rural size-resolved particles and transformation of NO2/SO2 to nanoparticle-bound NO3−/SO42−

This study investigates ammonium, nitrate, and sulfate (NH₄⁺, NO₃^?, and SO₄^2?) in size-resolved particles (particularly nano (PM_0.01–0.056)/ultrafine (PM_0.01–0.1)) and NO_x/SO₂ collected near a busy road and at a rural site. The average (mass) cumulative fraction of secondary inorganic aerosols (SO₄^2?+NO₃^?+NH₄⁺) in nano or ultrafine particles at the roadside was found to be three to four times that at the rural site. The above three secondary inorganic aerosol species were present in similar cumulative fractions in particles of size 1–18 μm at both sites; however, dissimilar fractions were observed for Cl^?, Na⁺, and K⁺. The nitrogen ratios (NRs: NR = NO₃^??N/(NO₃^??N + NO₂–N)), sulfur ratios (SRs: SR = SO₄^2??S/(SO₄^2??S + SO₂–S)), dNR/D_P (derivative of NR with respect to D_P (particle diameter)), and dSR/D_P (derivative of SR with respect to D_P) at the roadside were higher than those at the rural site for nano/ultrafine particles. At both sites (particularly the roadside), the nanoparticles had significantly higher dNR/D_P and dSR/D_P values than differently sized particles, implying that NO₃^?/SO₄^2? (from NO₂/SO₂ transformation or NO₃^?/SO₄^2? deposition) were present on these particles.     

Synthesis and characterization of magnetic Fe3O4@CaSiO3 composites and evaluation of their adsorption characteristics for heavy metal ions

A two-component material (Fe₃O₄@CaSiO₃) with an Fe₃O₄ magnetite core and layered porous CaSiO₃ shell from calcium nitrate and sodium silicate was synthesized by precipitation. The structure, morphology, magnetic properties, and composition of the Fe₃O₄@CaSiO₃ composite were characterized in detail, and its adsorption performance, adsorption kinetics, and recyclability for Cu²⁺, Ni²⁺, and Cr³⁺ adsorption were studied. The Fe₃O₄@CaSiO₃ composite has a 2D core–layer architecture with a cotton-like morphology, specific surface area of 41.56 m²/g, pore size of 16 nm, and pore volume of 0.25 cm³/g. The measured magnetization saturation values of the magnetic composite were 57.1 emu/g. Data of the adsorption of Cu²⁺, Ni²⁺, and Cr³⁺ by Fe₃O₄@CaSiO₃ fitted the Redlich–Peterson and pseudo-second-order models well, and all adsorption processes reached equilibrium within 150 min. The maximum adsorption capacities of Fe₃O₄@CaSiO₃ toward Cu²⁺, Ni²⁺, and Cr³⁺ were 427.10, 391.59, and 371.39 mg/g at an initial concentration of 225 mg/L and a temperature of 293 K according to the fitted curve with the Redlich–Peterson model, respectively. All adsorption were spontaneous endothermic processes featuring an entropy increase, including physisorption, chemisorption, and ion exchange; among these process, chemisorption was the primary mechanism. Fe₃O₄@CaSiO₃ exhibited excellent adsorption, regeneration, and magnetic separation performance, thereby demonstrating its potential applicability to removing heavy metal ions.

     

Organic carbon,total nitrogen,and water-soluble ions in clouds from a tropical montane cloud forest in Puerto Rico

Chemical characterization to determine the organic and nitrogen fractions was performed on cloud water samples collected in a mountaintop site in Puerto Rico. Cloud water samples showed average concentrations of 1.09 mg L^?1 of total organic carbon (TOC), of 0.85 mg L^?1 for dissolved organic carbon (DOC) and of and 1.25 mg L^?1 for total nitrogen (TN). Concentrations of organic nitrogen (ON) changed with the origin of the air mass. Changes in their concentrations were observed during periods under the influence of African dust (AD). The ON/TN ratios were 0.26 for the clean and 0.35 for the AD periods. Average concentrations of all these species were similar to those found in remote environments with no anthropogenic contribution. In the AD period, for cloud water the concentrations of TOC were 4 times higher and TN were 3 times higher than during periods of clean air masses associated with the trade winds. These results suggest that a significant fraction of TOC and TN in cloud and rainwater is associated to airborne particulate matter present in dust. Functional groups were identified using proton nuclear magnetic resonance (¹H NMR) spectroscopy. This characterization led to the conclusion that water-soluble organic compounds in these samples are mainly aliphatic oxygenated compounds, with a small amount of aromatics. The ion chromatography results showed that the ionic species were predominantly of marine origin, for air masses with and without African dust influence, with cloud water concentrations of NO₃^? and NH₄⁺ much lower than from polluted areas in the US. An increase of such species as SO₄^2?, Cl^?, Mg²⁺, K⁺ and Ca²⁺ was seen when air masses originated from northwest Africa. The changes in the chemical composition and physical properties of clouds associated with these different types of aerosol particles could affect on cloud formation and processes.