Photooxidation of arsenite by natural goethite in suspended solution

Iron and arsenic have been found to coexist in a water environment and the fate of arsenite in the aquatic system is influenced by iron. Goethite is a form of iron hydroxide, which is commonly found in sediments. In previous studies, we have used iron complexes to degrade organic pollutants. Results have shown that some organic pollutants could be totally degraded by iron complexes and our work indicated that iron might cause conversion of arsenic when irradiated. This work attempts to investigate the conversion of arsenite [As(III)] using natural goethite, as the iron source, to quantify the effect of various factors on photooxidation. We also consider the possible mechanism for photooxidation of As(III) using a suspension of natural goethite. The As(III) concentration variation under illumination was compared with the one in the dark to quantify the contribution of light to As(III) oxidation to As(V) in goethite suspended solution. The experiments under N₂ and air atmosphere confirmed the participation of dissolved oxygen. The photooxidation efficiency of As(III) under different conditions was compared to determine the effect of different environmental factors such as pH value, goethite concentration, and humic acid concentration on the photooxidation reaction. In the solution containing 100 μg L^?1 arsenite and 0.1 g?L^?1 suspended goethite at pH 3.0, nearly 80 % of As(III) was photooxidized after irradiation by a 250-W metal halogen lamp (λ?≥?313 nm) after 6 h. The effects of initial pH and goethite concentration and humic acid concentration were all examined. The results show that the greatest efficiency of photooxidation of As(III) was at pH 3.0. The extent of photooxidation decreased with increasing goethite concentration and fell sharply in the presence of humic acid under the conditions in this work. Although about 80 % of As(III) was photooxidized after irradiation by a 250-W halogen lamp at pH 3.0 in the presence of goethite suspension, photooxidation was also affected by factors such as pH, concentration of goethite, and presence of humic acid. The scavenger experiments showed that the HO? radical and photogenerated hole are the predominant oxidants in this system responsible for 87.1 % oxidation of As(III), while HO ₂ ^? /O ₂ ^?? is responsible for 12.9 % oxidation of As(III).     

Accumulation, transformation, and release of inorganic arsenic by the freshwater cyanobacterium Microcystis aeruginosa

Arsenic (As) as a major hazardous metalloid was affected by phytoplankton in many aquatic environments. The toxic dominant algae Microcystis aeruginosa was exposed to different concentrations of inorganic arsenic (arsenate or arsenite) for 15 days in BG11 culture media. Arsenic accumulation, toxicity, and speciation in M. aeruginos as well as the changes of As species in media were examined. M. aeruginosa has a general well tolerance to arsenate and a definite sensitivity to arsenite. Additionally, arsenate actively elevated As methylation by the algae but arsenite definitely inhibited it. Interestingly, the uptake of arsenite was more pronounced than that of arsenate, and it was correlated to the toxicity. Arsenate was the predominant species in both cells and their growth media after 15 days of exposure to arsenate or arsenite. However, the amount of the methylated As species in cells was limited and insignificantly affected by the external As concentrations. Upon uptake of the inorganic arsenic, significant quantities of arsenate as well as small amounts of arsenite, DMA, and MMA were produced by the algae and, in turn, released back into the growth media. Bio-oxidation was the first and primary process and methylation was the minor process for arsenite exposures, while bioreduction and the subsequent methylation were the primary metabolisms for arsenate exposures. Arsenic bioaccumulation and transformation by M. aeruginosa in aquatic environment should be paid more attention during a period of eutrophication.     

Arsenic sorption by red mud-modified biochar produced from rice straw

Red mud-modified biochar (RM-BC) has been produced to be utilized as a novel adsorbent to remove As because it can effectively combine the beneficial features of red mud (rich metal oxide composition and porous structure) and biochar (large surface area and porous structure properties). SEM-EDS and XRD analyses demonstrated that red mud had loaded successfully on the surface of biochar. With the increasing of pH in solution, arsenate (As(V)) adsorption on RM-BC decreased while arsenite (As(III)) increased. Arsenate adsorption kinetics process on RM-BC fitted the pseudo-second-order model, while that of As(III) favored the Elovich model. All sorption isotherms produced superior fits with the Langmuir model. RM-BC exhibited improved As removal capabilities, with a maximum adsorption capacity (Q_max) for As(V) of 5923 μg g^?1, approximately ten times greater than that of the untreated BC (552.0 μg g^?1). Furthermore, it has been indicated that the adsorption of As(V) on RM-BC may be strongly associated with iron oxides (hematite and magnetite) and aluminum oxides (gibbsite) by X-ray absorption near-edge spectroscopy (XANES), which was possibly because of surface complexation and electrostatic interactions. RM-BC may be used as a valuable adsorbent for removing As in the environment due to the waste materials being relatively abundant.     

Responses of kinetics and capacity of phenanthrene sorption on sediments to soil organic matter releasing

Soil organic matter (SOM) releasing with dissolved organic matter (DOM) formed in solution was confirmed in a sediment/water system, and the effects of SOM releasing on the sorption of phenanthrene on sediments were investigated. Inorganic salt (0–0.1 mol L^?1 NaCl) was used to adjust SOM releasing, and two sediments were prepared, the raw sediment (S1) from Weihe River, Shann’xi, China, and the eluted sediments with and without DOM supernatant remained, termed as S2a and S2b, respectively. The FTIR and ¹H NMR analysis indicate that the low molecular weight hydrophilic SOM fraction released prior to the high molecular weight hydrophobic fraction. As a response, phenanthrene sorption kinetics on S1 showed atypical and expressed as three stages: rapid sorption, pseudo sorption with partial desorption, and slow sorption, thus a defined “sorption valley” occurred in kinetic curve. In all cases, partition dominates the sorption, and sorption capacity (K_d) ranked as S2b > S1 > S2a. Compared with the alterations of sediment characters, DOM solubilization produced by SOM releasing exhibited a greater inhibitory effect on sorption with a relative contribution of 0.67. Distribution coefficients (K_doc) of PHE into DOM clusters were 2.10?×?10⁴–4.18?×?10⁴ L kg^?1, however a threshold concentration of 6.83 mg L^?1 existed in DOM solubilization. The study results will help to clarify PAHs transport and their biological fate in a sediment/water system.     

Adsorption/desorption of arsenite and arsenate on chitosan and nanochitosan

Equilibrium sorption studies of anionic species of arsenite, As(III) ions and arsenate As(V) ions onto two biosorbents, namely, chitosan and nanochitosan, have been investigated and compared. The results and trends in the sorption behavior are novel, and we have observed during the sorption process of the As(III) and As(V) on chitosan, a slow process of desorption occurred after an initial maximum adsorption capacity was achieved, before reaching a final but lower equilibrium adsorption capacity. The same desorption trend, however, is not observed on nanochitosan. The gradual desorption of As(III) and As(V) in the equilibrium sorption on chitosan is attributed to the different fractions of the dissociated forms of arsenic on the adsorbent surface and in solution and the extent of protonation of chitosan with the changing of solution pH during sorption. The change of solution pH during the sorption of arsenite ions on chitosan was also influenced by the interaction between the buffering effect of the arsenite species in the aqueous medium and the physical properties of chitosan. The final equilibrium adsorption capacity of chitosan for As(III) and As(V) was found to be around 500 and 8000 μg/g, respectively, whereas the capacities on nanochitosan are 6100 and 13,000 μg/g, respectively.

     

Quantifying interactions between propranolol and dissolved organic matter (DOM) from different sources using fluorescence spectroscopy

Beta blockers are widely used pharmaceuticals that have been detected in the environment. Interactions between beta blockers and dissolved organic matter (DOM) may mutually alter their environmental behaviors. To assess this potential, propranolol (PRO) was used as a model beta blocker to quantify the complexation with DOM from different sources using the fluorescence quenching titration method. The sources of studied DOM samples were identified by excitation–emission matrix spectroscopy (EEMs) combined with fluorescence regional integration analysis. The results show that PRO intrinsic fluorescence was statically quenched by DOM addition. The resulting binding constants (log K _oc) ranged from 3.90 to 5.20, with the surface-water-filtered DOM samples claiming the lower log K _oc and HA having the highest log K _oc. Log K _oc is negatively correlated with the fluorescence index, biological index, and the percent fluorescence response (P _i,n) of protein-like region (P _I,n) and the P _i,n of microbial byproduct-like region (P _II,n) of DOM EEMs, while it is correlated positively with humification index and the P _i,n of UVC humic-like region (P _III,n). These results indicate that DOM samples from allochthonous materials rich in aromatic and humic-like components would strongly bind PRO in aquatic systems, and autochthonous DOM containing high protein-like components would bind PRO more weakly.     

Arsenic accumulation and translocation in the submerged macrophyte Hydrilla verticillata (L.f.) Royle

Worldwide contamination of arsenic in aquatic systems requires the development of a cost-effective, in situ phytoremediation technology. Hydrilla verticillata (L.f.) Royle, a submerged macrophyte widely distributed throughout the world, has the potential to effectively remove heavy metals from water. In order to understand the potential of H. verticillata for As phytofiltration and its impacts on As cycling in the water system, we investigated As accumulation, speciation and translocation in H. verticillata plants. Plant shoots showed a significant accumulation of As, with a maximum of >700 μg g⁻¹ dry weight (DW) after exposure to 20 μM arsenate [As(V)] or arsenite [As(III)] for 4 d, with no significant differences between the As(V) and As(III) treatments (P > 0.05). In addition, results of an in planta transport experiment showed that, after exposure of root and shoot to 2 μM As(V) and As(III) for 4 d, the bioconcentration factor (BCF) in roots for As(V) was almost twofold than that of As(III). Higher As BCFs in roots compared to shoots was also observed. Arsenic accumulated primarily in the cell walls of root cells (>73% of the total As in roots) and in the soluble parts of leaves (>60% of the total As in leaves). Regardless of the form of As supplied [As(III) or As(V)], As(V) was the dominant form in roots and As(III) was the dominant form in leaves. Further, basipetal translocation of As in this plant (?17%) was markedly higher than acropetal translocation (?3%). Because of accumulation of As in the shoot and immobilization of As below ground in roots, H. verticillata is a potential As phytofiltrator for bioremediation.     

Isolation and characterization of dissolved organic matter fractions from antialgal products of Microcystis aeruginosa

An antialgal bacterium, Streptomyces sp. HJC-D1, was applied for the biodegradation of cyanobacterium Microcystis aeruginosa, and the isolation and characterization of dissolved organic matter (DOM) fractions in antialgal products were studied. Results showed the the growth of M. aeruginosa was significantly inhibited by the cell-free filtrate of Streptomyces sp. HJC-D1 with the growth inhibition of 86?±?7 %. The antialgal products were divided using resin adsorbents into the hydrophilic fraction (HPI), hydrophobic acid (HPO-A), transphilic acid (TPI-A), hydrophobic neutral and transphilic neutral, and then the five fractions were analyzed by the 3-D fluorescence spectroscopy, gel permeation chromatography, and Fourier transform infrared spectroscopy. The results indicated that the HPI component was the most abundant DOM fraction in the antialgal products, and its concentration was increased with the increase of cell-free filtrate concentration. The fluorescence peak location and intensity analysis showed that the protein-, fulvic-, and humic-like substances were dominant in the HPI, HPO-A, and TPI-A fractions, and intensities of the relevant fluorescence peaks were stronger in the experimental groups than those of the control groups. It was also found that the number-average molecular weight of DOM fractions ranged from 245 to 1,452 g mol^?1, and thereinto organic acids such as HPO-A and TPI-A exhibited lower molecular weights.     

Alginate beads containing water treatment residuals for arsenic removal from water—formation and adsorption studies

Water treatment residuals (WTRs) produced in large quantities during deironing and demanganization of infiltration water, due to high content of iron and manganese oxides, exhibit excellent sorptive properties toward arsenate and arsenite. Nonetheless, since they consist of microparticles, their practical use as an adsorbent is limited by difficulties with separation from treated solutions. The aim of this study was entrapment of chemically pretreated WTR into calcium alginate polymer and examination of sorptive properties of the obtained composite sorbent toward As(III) and As(V). Different products were formed varying in WTR content as well as in density of alginate matrix. In order to determine the key parameters of the adsorption process, both equilibrium and kinetic studies were conducted. The best properties were exhibited by a sorbent containing 5 % residuals, formed in alginate solution with a concentration of 1 %. In slightly acidic conditions (pH 4.5), its maximum sorption capacity was 3.4 and 2.9 mg g^?1 for As(III) and As(V), respectively. At neutral pH, the adsorption effectiveness decreased to 3.3 mg As g^?1 for arsenites and to 0.7 mg As g^?1 for arsenates. The presence of carboxylic groups in polymer chains impeded in neutral conditions the diffusion of anions into sorbent beads; therefore, the main rate-limiting step of the adsorption, mainly in the case of arsenates, was intraparticle diffusion. The optimal condition for simultaneous removal of arsenates and arsenites from water by means of the obtained composite sorbent is slightly acidic pH, ensuring similar adsorption effectiveness for both arsenic species.     

Accelerated photo-transformation of 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) in water by dissolved organic matter

The ubiquitous dissolved organic matter (DOM) has an important influence on transformation of organic contaminants through the production of reactive substances, such as ^?OH, ¹O₂, and ³DOM*. The photolysis of a higher chlorinated polychlorinated biphenyl (PCB) congener (2,2′,4,4′,5,5′-hexachlorobiphenyl, PCB 153) under simulated sunlight in presence of humic acid (HA) was investigated. Degradation of PCB 153 was accelerated significantly by the addition of HA, with a rate constant of 0.0214, 0.0413, and 0.0358 h^?1 in the initial 18 h of irradiation in presence of 1, 5, and 20 mg/L HA, respectively. The main photodegradation products analyzed by gas chromatography mass spectrometry were 4-hydroxy-2,2′,4′,5,5′-pentaCB and 2,4,5-trichlorobenzoic acid. Main reactive species involved were determined by the electron spin-resonance spectroscopy, including ¹O₂ and ^?OH. Special scavengers were added to elucidate the photolysis mechanisms. By using the specific scavengers, it turned out that ^?OH accounted for 29.3 % of the degradation, and the intra-DOM reactive species (¹O₂, ^?OH, and ³DOM*) accounted for 59.6 % of the degradation. Photo-transformation sensitized by DOM, which involves both aqueous and intra-DOM reactions of PCBs with reactive species, may be one of the most important mechanisms for natural attenuation of PCBs.     

Sorption of cyromazine on humic acid: Effects of pH,ionic strength and foreign ions

Cyromazine (CY) is a triazine pesticide used as an insect growth inhibitor for fly control in cattle manure, field crops, vegetables, and fruits. Sorption of CY onto humic acid (HA) may affect its environmental fate. In this study, HA was used to investigate the sorption of CY at different solution chemistry conditions (pH, ionic strength) and in the presence of foreign ions and norfloxacin. All sorption isotherms fitted well with the Freundlich and Langmuir models. The sorption reached a maximum at initial pH 4.0 over the initial pH range of 3.0–7.0, implying that the primary sorption mechanism was cation exchange interaction between CY⁺ species and the negatively charged functional groups of HA. Increasing Ca²⁺ concentration resulted in a considerable reduction in the K _d values of CY, hinting that Ca²⁺ had probably competed with CY⁺ for the cation exchange sites on the surfaces of HA. The sorption of CY on HA in different ionic media followed the order of NH₄Cl ≈ KCl > K₂SO₄ > ZnCl₂ ≈ CaCl₂ at pH 5.0. Spectroscopic evidence demonstrated that the amino groups and triazine ring of CY was responsible for sorption onto HA, while the carboxyl group and the O-alkyl structure of HA participated in adsorbing CY.     

Effect of silicate supplementation on the alleviation of arsenite toxicity in 93-11 (Oryza sativa L. indica)

Chronic exposure to arsenic (As) in rice has raised many health and environmental problems. As reported, great variation exists among different rice genotypes in As uptake, translocation, and accumulation. Under hydroponic culture, we find that the Chinese wild rice (Oryza rufipogon; acc. 104624) takes up the most arsenic among tested genotypes. Of the cultivated rice, the indica cv. 93-11 has the lowest arsenic translocation factor value but accumulates the maximum concentration of arsenic followed by Nipponbare, Minghui 86, and Zhonghua 11. Higher level of arsenite concentration (50 μM) can induce extensive photosynthesis and root growth inhibition, and cause severe oxidative stress. Interestingly, external silicate (Si) supplementation has significantly increased the net photosynthetic rate, and promoted root elongation, as well as strongly ameliorated the oxidative stress by increasing the activities of antioxidant enzymes superoxide dismutase, ascorbate peroxidase, and peroxidase in roots and/or leaves of 93-11 seedlings. Notably, 1.873 mM concentration of Si considerably decreases the total As uptake and As content in roots, but significantly increases the As translocation from roots to shoots. In contrast, Si supplementation with 1.0 mM concentration significantly increases the total As uptake and As concentrations in roots and shoots of 93-11 seedlings after 50 μM arsenite treatment for 6 days.     

Survey of cyanobacterial toxins in Czech water reservoirs—the first observation of neurotoxic saxitoxins

The environmental occurrence and concentrations of cyanobacterial toxins (cyanotoxins) were investigated in the Czech Republic. Concentrations of microcystins (MCs), cylindrospermopsin (CYN) or saxitoxins (STXs) were determined immunochemically by ELISA assays in 30 water samples collected from the surface layers of 19 reservoirs during the summer season of 2010. MCs were detected in 18 reservoirs and 83 % of samples, with median and maximal concentration being 1.5 and 18.6 μg/L, respectively. The high frequency of MC occurrence coincided with prevalence of cyanobacterium Microcystis sp., which was detected in 87 % samples, followed by Dolichospermum (Anabaena) sp. observed in 33 % samples. CYN was detected by ELISA only in one sample at a concentration of 1.2 μg/L. STXs presence was indicated for the first time in Czech water reservoirs when the toxins were found at low concentrations (0.03–0.04 μg/L) in two samples (7 %) collected from two different reservoirs, where STXs co-occurred with MCs and eventually also with CYN. In both STX-positive samples, the phytoplankton community was dominated by Microcystis sp., but Dolichospermum sp. and/or Aphanizomenon sp. were also present as putative producers of STX and/or CYN. Cyanotoxins commonly occurred in Czech water reservoirs, and MCs frequently at concentrations possibly associated with human health risks. MCs were the most prevalent and abundant cyanotoxins, but also other cyanotoxins were detected, though sporadically. Further research and regulatory monitoring of cyanotoxins other than MCs is therefore required.     

Adsorption and removal of As(V) and As(III) using Zr-loaded lysine diacetic acid chelating resin

An adsorption process for the removal of As(V) and As(III) was evaluated under various conditions using zirconium(IV) loaded chelating resin (Zr-LDA) with lysine-Nalpha,Nalpha diacetic acid functional groups. Arsenate ions strongly adsorbed in the pH range from 2 to 5, while arsenite was adsorbed between pH 7 and 10.5. The sorption mechanism is an additional complexation between arsenate or arsenite and Zr complex of LDA. Adsorption isotherm data could be well interpreted by Langmuir equation for As(V) at pH 4 and As(III) at pH 9 with a binding constant 227.93 and 270.47 dm3 mol(-1) and capacity constant 0.656 and 1.1843 mmol g(-1), respectively. Regeneration of the resin was carried out for As(V) using 1 M NaOH. Six adsorption/desorption cycles were performed without significant decrease in the uptake performance. Column adsorption studies showed that the adsorption of As(V) is more favorable compared to As(III), due to the faster kinetics of As(V) compared to As(III). Influence of the coexisting ions on the adsorption of As(V) and As(III) was studied. The applicability of the method for practical water samples was studied.     

Removal of arsenic species from water by batch and column operations on bagasse fly ash

Bagasse fly ash (BFA, a sugar industrial waste) was used as low-cost adsorbent for the uptake of arsenate and arsenite species from water. The optimum conditions for the removal of both species of arsenic were as follows: pH 7.0, concentration 50.0 μg/L, contact time 50.0 min, adsorbent dose 3.0 g/L, and temperature 20.0 °C, with 95.0 and 89.5 % removal of arsenate and arsenite, respectively. The Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich adsorption isotherms were used to analyze the results. The results of these models indicated single-layer uniform adsorption on heterogeneous surface. Thermodynamic parameters, i.e., ΔG°, ΔH°, and ΔS°, were also calculated. At 20.0 to 30.0 °C, the values of ΔG° lie in the range of ?4,722.75 to ?4,878.82 and ?4,308.80 to ?4,451.73 while the values of ΔH° and ΔS° were ?149.90 and ?121.07, and 15.61 and 14.29 for arsenate and arsenite, respectively, indicating that adsorption is spontaneous and exothermic. Pseudo-first-order kinetics was followed. In column experiments, the adsorption decreased as the flow rate increased with the maximum removal of 98.9 and 95.6 % for arsenate and arsenite, respectively. The bed depth service time and Yoon and Nelson models were used to analyze the experimental data. The adsorption capacity (N _o) of BFA on column was 3.65 and 2.98 mg/cm³ for arsenate and arsenite, respectively. The developed system for the removal of arsenate and arsenite species is economic, rapid, and capable of working under natural conditions. It may be used for the removal of arsenic species from any contaminated water resources.     

Mammalian cell-line based toxicological evaluation of paper mill black liquor treated in a soil microcosm by indigenous alkalo-tolerant Bacillus sp

Organic pollutants present in the soil of a microcosm containing pulp and paper mill black liquor were extracted with hexane/acetone (1:1 v/v) to study the biodegradation and detoxification potential of a Bacillus sp. gas chromatography-mass spectroscopic (GC-MS) analysis performed after biodegradation showed formation of simpler compounds like p-hydroxyhydrocinnamic acid (retention time [RT] 19.3 min), homovanillic acid methyl ester (RT 21.6 min) and 3,5-dimethoxy-p-coumaric alcohol (RT 24.7 min). The methyltetrazolium (MTT) assay for cytotoxicity, 7-ethoxyresorufin-O-deethylase (EROD) assay for dioxin-like behavior and alkaline comet assay for genotoxicity were carried out in the human hepatocarcinoma cell line HuH-7 before and after bacterial treatment. Bioremediation for 15 days reduced toxicity, as shown by a 139-fold increase in black liquor’s LC₅₀ value, a 343-fold reduction in benzo(a)pyrene equivalent value and a 5-fold reduction in olive tail moment. The EROD assay positively correlated with both the MTT and comet assays in post biodegradation toxicity evaluation.     

Copper (II) adsorption by the extracellular polymeric substance extracted from waste activated sludge after short-time aerobic digestion

The extracellular polymeric substance (EPS) extracted from waste activated sludge (WAS) after short-time aerobic digestion was investigated to be used as a novel biosorbent for Cu²⁺ removal from water. The EPS consisted of protein (52.6 %, w/w), polysaccharide (30.7 %, w/w), and nucleic acid (16.7 %, w/w). Short-time aerobic digestion process of WAS for about 4 h promoted the productivity growth of the EPS for about 10 %. With a molecular weight of about 1.9?×?10⁶ Da, the EPS showed a linear structure with long chains, and contained carboxyl, hydroxyl, and amino groups. The sorption kinetics was well fit for the pseudo-second-order model, and the maximum sorption capacity of the EPS (700.3 mg Cu²⁺/g EPS) was markedly greater than those of the reported biosorbents. Both Langmuir model and Freundlich model commendably described the sorption isotherm. The Gibbs free energy analysis of the adsorption showed that the sorption process was feasible and spontaneous. According to the complex results of multiple analytical techniques, including scanning electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy, etc., the adsorption process took place via both physical and chemical sorption, but the electrostatic interaction between sorption sites with the functional groups and Cu²⁺ is the major mechanism.     

Desorption of arsenic from clay and humic acid-coated clay by dissolved phosphate and silicate

Arsenic (As) contaminated aquifers contain iron minerals and clays that strongly bind As at their surfaces. It was suggested that As mobilization is driven by natural organic matter (including fulvic acids (FA) and humic acids (HA)) present in the aquifers either via providing reducing equivalents for reductive dissolution of Fe(III) (hydr)oxides or via competitive desorption of As from the mineral surfaces. In the present study we quantified sorption of As(III) and As(V) to Ca(2+)-homoionized illite (IL) and to kaolinite (Kao) as well as to HA-coated clays, i.e., illite-HA (IL-HA) and kaolinite-HA (Kao-HA) at neutral pH. Clay-HA complexes sorbed 28-50% more As than clay-only systems upon addition of 100μM As(III)/As(V) to 0.5g of clay or HA-clay with Ca(2+) probably playing an important role for HA binding to the clay surface and As binding to the HA. When comparing sorption of As(V) and As(III) to clay and HA-clay complexes, As(V) sorption was generally higher by 15-32% than sorption of As(III) to the same complexes. IL and IL-HA sorbed 11-28% and 6-11% more As compared to Kao and Kao-HA, respectively. In a second step, we then followed desorption of As from Kao, Kao-HA, IL and IL-HA by 100 and 500μM phosphate or silicate both at high (0.41-0.77μmol As/g clay), and low (0.04 to 0.05μmol As/g clay) As loadings. Phosphate desorbed As to a larger extent than silicate regardless of the amount of As loaded to clay minerals, both in the presence and absence of HA, and both for illite and kaolinite. At high loadings of As, the desorption of both redox species of As from clay-HA complexes by phosphate/silicate ranged from 32 to 72% compared to 2-54% in clay only systems meaning that As was desorbed to a larger extent from HA-coated clays compared to clay only systems. When comparing As(III) desorption by phosphate/silicate to As(V) desorption in high As-loading systems, there was no clear trend for which As species is desorbed to a higher extent in the four clay systems meaning that both As species behave similarly regarding desorption from clay surfaces by phosphate/silicate. Similarly, no significant differences were found in high As-loading systems in the amount of As desorbed by phosphate/silicate when comparing Kao vs. IL and Kao-HA vs IL-HA systems meaning that both clay types behave similarly regarding desorption of As by phosphate/silicate. At low As loadings, up to 80% of As was desorbed by phosphate and silicate with no noticeable differences being observed between different As species, different types of clay, clay vs clay-HA or the type of desorbant (phosphate and silicate). The results of this study showed that HA sorption to Ca(2+)-homoionized clay minerals can increase As binding to the clay although the As sorbed to the clay-HA is also released to a greater extent by competing ions such as phosphate and silicate. Desorption of As depended on the initial loadings of As onto the clay/clay-HA. Based on our results, the effect of humic substances on sorption of As and on desorption of As by phosphate and silicate has to be considered in order to fully understand and evaluate the environmental behavior of As in natural environments.     

Particle size distribution of n-alkanes and polycyclic aromatic hydrocarbons (PAHS) in urban and industrial aerosol of Algiers,Algeria

The distribution of ambient air n-alkanes and polycyclic aromatic hydrocarbons (PAHs) associated to particles with aerodynamic diameters lesser than 10 μm (PM₁₀) into six fractions (five stages and a backup filter) was studied for the first time in Algeria. Investigation took place during September of 2007 at an urban and industrial site of Algiers. Size-resolved samples (<0.49, 0.49–0.95, 0.95–1.5, 1.5–3.0, 3.0–7.2, and7.2–10 μm) were concurrently collected at the two sampling sites using five-stage high-volume cascade impactors. Most of n-alkanes (~72 %) and PAHs (~90 %) were associated with fine particles ≤1.5 μm in both urban and industrial atmosphere. In both cases, the n-alkane contents exhibited bimodal or weakly bimodal distribution peaking at the 0.95–1.5-μm size range within the fine mode and at 7.3–10 μm in the coarse mode. Low molecular weight PAHs displayed bimodal patterns peaking at 0.49–0.95 and 7.3–10 μm, while high molecular weight PAHs exhibited mono-modal distribution with maximum in the <0.49-μm fraction. While the mass mean diameter of total n-alkanes in the urban and industrial sites was 0.70 and 0.84 μm, respectively, it did not exceed 0.49 μm for PAHs. Carbon preference index (~1.1), wax% (10.1–12.8), and the diagnostic ratios for PAHs all revealed that vehicular emission was the major source of these organic compounds in PM₁₀ during the study periods and that the contribution of epicuticular waxes emitted by terrestrial plants was minor. According to benzo[a]pyrene-equivalent carcinogenic power rates, ca. 90 % of overall PAH toxicity across PM₁₀ was found in particles ≤0.95 μm in diameter which could induce adverse health effects to the population living in these areas.