Heterogenous photocatalytic degradation kinetics and detoxification of an urban wastewater treatment plant effluent contaminated with pharmaceuticals

Degradation kinetics and mineralization of an urban wastewater treatment plant effluent contaminated with a mixture of pharmaceutical compounds composed of amoxicillin (10 mg L⁻¹), carbamazepine (5 mg L⁻¹) and diclofenac (2.5 mg L⁻¹) by TiO₂ photocatalysis were investigated. The photocatalytic effect was investigated using both spiked distilled water and actual wastewater solutions. The process efficiency was evaluated through UV absorbance and TOC measurements. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Lepidium sativum) was performed to evaluate the potential toxicity of the oxidation intermediates. A pseudo-first order kinetic model was found to fit well the experimental data. The mineralization rate (TOC) of the wastewater contaminated with the pharmaceuticals was found to be really slow (t_1/2 = 86.6 min) compared to that of the same pharmaceuticals spiked in distilled water (t_1/2 = 46.5 min). The results from the toxicity tests of single pharmaceuticals, their mixture and the wastewater matrix spiked with the pharmaceuticals displayed a general accordance between the responses of the freshwater aquatic species (P. subscapitata > D. magna). In general the photocatalytic treatment did not completely reduce the toxicity under the investigated conditions (maximum catalyst loading and irradiation time 0.8 g TiO₂ L⁻¹ and 120 min respectively).     

Comparison of toxicity and release rates of Cu and Zn from anti-fouling paints leached in natural and artificial brackish seawater

Biocide-containing anti-fouling paints are regulated and approved according to the added active ingredients, such as Cu. Biocide-free paints are considered to be less environmentally damaging and do not need an approval. Zn, a common ingredient in paints with the potential of causing adverse effects has received only minor attention. Laboratory experiments were conducted in artificial brackish seawater (ASW) and natural brackish seawater (NSW) to quantify release rates of Cu and Zn from biocide-containing and biocide-free labeled eroding anti-fouling paints used on commercial vessels as well as leisure boats. In addition, organisms from three trophic levels, the crustacean Nitocra spinipes, the macroalga Ceramium tenuicorne and the bacteria Vibrio fischeri, were exposed to Cu and Zn to determine the toxicity of these metals. The release rate of Cu in NSW was higher from the paints for professional use (3.2-3.6 µg cm⁻² d^− 1) than from the biocide leaching leisure boat paint (1.1 µg cm⁻² d^− 1). Biocide-free paints did leach considerably more Zn (4.4-8.2 µg cm⁻² d^− 1) than biocide-containing leisure boat paint (3.0 µg cm⁻² d^− 1) and ship paints (0.7-2.0 µg cm⁻² d^− 1). In ASW the release rates of both metals were notably higher than in NSW for most tested paints. The macroalga was the most sensitive species to both Cu (EC₅₀ = 6.4 µg l^− 1) and Zn (EC₅₀ = 25 µg l^− 1) compared to the crustacean (Cu, LC₅₀ = 2000 µg l^− 1 Zn, LC₅₀ = 890 µg l^− 1), and the bacteria (Cu, EC₅₀ = 800 µg l^− 1 and Zn, EC₅₀ = 2000 µg l^− 1). The results suggest that the amounts of Zn and Cu leached from anti-fouling paints may attain toxic concentrations in areas with high boat density. To fully account for potential ecological risk associated with anti-fouling paints, Zn as well as active ingredients should be considered in the regulatory process.     

Fate of pharmaceuticals in contaminated urban wastewater effluent under ultrasonic irradiation

The application of sonolysis (US) for remediation of wastewater is an area of increasing interest. The aim of this study was to evaluate the ultrasonic (US) process on the degradation of pharmaceuticals (diclofenac (DCF), amoxicillin (AMX), carbamazepine (CBZ)) in single solutions and also in three mixtures spiked in urban wastewater effluent. Several operating conditions, such as power density (25-100 W L⁻¹), initial substrate concentrations (2.5-10 mg L⁻¹), initial solution pH (3-11), and air sparging were varied for the evaluation and understanding of the process. The degradation (as assessed by measuring UV absorbance), the generation of hydroxyl radicals (as assessed measuring H₂O₂ concentration), the mineralization (in terms of TOC and COD removal), and the aerobic biodegradability (as assessed by the BOD₅/COD ratio) were monitored during sonication. Ecotoxicity to Daphnia magna, Pseudokirchneriella subcapitata and Lepidium sativum before and after treatment was also evaluated. It was found that the pharmaceuticals conversion is enhanced at increased applied power densities, acidic conditions and in the presence of dissolved air. The reaction rate increases with increasing initial concentration of single pharmaceuticals but it remains constant in the mixtures, indicating different kinetic regimes (i.e. first and zero order respectively). Mineralization is a slow process as reaction by-products are more stable than pharmaceuticals to total oxidation; nonetheless, they are also more readily biodegradable. The toxicity of the wastewater samples before and after contamination with pharmaceuticals both in mixtures and in single substance-containing solutions was observed more severely on P. subcapitata; a fact that raises concerns in regards to the discharge of such effluents. D. magna displayed less sensitivity compared to P. subcapitata because it belongs in a lower taxonomic species than D. magna. The germination index of L. sativum in the presence of the drugs' mixture was stimulated instead of inducing any toxicity effect and this might be attributed to the fact the sample, laden with very low drug concentrations was able to act as a provider of additional nutrient elements.     

Water, vegetation and sediment gradients in submerged aquatic vegetation mesocosms used for low-level phosphorus removal

Gradients in phosphorus (P) removal and storage were investigated over 6 years using mesocosms (each consisting of three tanks in series) containing submerged aquatic vegetation (SAV) grown on muck and limerock (LR) substrates. Mean inflow total P concentrations (TP) of 32 μg L⁻¹ were reduced to 15 and 17 μg L⁻¹ in the muck and LR mesocosms, respectively. Mesocosm P loading rates (mean = 1.75 g m⁻² year⁻¹) varied widely during the study and were not correlated with outflow TP, which instead varied seasonally with lowest monthly mean values in December and January.The mesocosms initially were stocked with Najas guadalupensis, Ceratophyllum demersum, and Chara zeylanica, but became dominated by C. zeylanica. At the end of the study, highest vegetative biomass (1.1 and 1.4 kg m⁻² for muck and LR substrates) and tissue P content (1775 and 1160 mg kg⁻¹) occurred in the first tank in series, and lowest biomass (1.0 and 0.2 kg m⁻²) and tissue P (147 and 120 mg kg⁻¹) in the third tank. Sediment accretion rates (2.5, 1.9 and 0.9 cm yr⁻¹ on muck substrates), accrued sediment TP (378, 309 and 272 mg kg⁻¹), and porewater soluble reactive P (SRP) concentrations (40, 6 and 4 μg L⁻¹) in the first, second and third tanks, respectively, exhibited a similar decreasing spatial trend. Plant tissue calcium (Ca) near mesocosm inflow (19-30% dry weight) and outflow (23-26%) were not significantly different, and sediment Ca was also similar (range of 24 to 28%) among sequential tanks.Well-defined vegetation and sediment enrichment gradients developed in SAV wetlands operated under low TP conditions. While the mesocosm data did not reflect deterioration in treatment performance over 6 years, accumulation of P-enriched sediments near the inflow could eventually compromise hydraulic storage and P removal effectiveness of these shallow systems.     

Evidences of non-reactive mercury-selenium compounds generated from cultures of Pseudomonas fluorescens

This work was designed to determine chemically inert mercury-selenium (Hg-Se) compounds formed in a culture of Pseudomonas fluorescens exposed to Hg²⁺ and Se^IV (selenite). To isolate these compounds, different digestion methods were studied and sodium dodecyl sulfate (SDS) lysis was selected. The Hg⁰ and non-reactive Hg were determined in two series of cultures containing 0.0-6.00 μg L⁻¹ Se^IV (0.0-76.0 μmol L⁻¹) in combination with low 5.00 μg L⁻¹ (0.025 μmol L⁻¹) or high 100 μg L⁻¹ (0.500 μmol L⁻¹) Hg²⁺. It was found that Hg⁰ formed in the culture decreased with the increase of initial Se^IV, while the non-reactive Hg increased with the Se^IV. In cultures with low initial [Hg²⁺], a median Se^IV (2.0 μg L⁻¹ or 25.3 μmol L⁻¹) resulted in about 70% of the added Hg²⁺ sequestered as non-reactive Hg, and in culture with high initial Hg²⁺, about 40% was sequestered. P. fluorescens was proved to be indispensible for the formation of the non-reactive Hg-Se compounds. The Hg:Se molar ratio in the non-reactive Hg-Se compounds was close to 1, suggesting the existence of mercuric selenide in cells. Mechanisms for the formation of the non-reactive Hg-Se compounds are proposed.     

Atmospheric NH3 and NO2 concentration and nitrogen deposition in an agricultural catchment of Eastern China

To assess the atmospheric environmental impacts of anthropogenic reactive nitrogen in the fast-developing Eastern China region, we measured atmospheric concentrations of nitrogen dioxide (NO₂) and ammonia (NH₃) as well as the wet deposition of inorganic nitrogen (NO₃⁻ and NH₄⁺) and dissolved organic nitrogen (DON) levels in a typical agricultural catchment in Jiangsu Province, China, from October 2007 to September 2008_. The annual average gaseous concentrations of NO₂ and NH₃ were 42.2 μg m⁻³ and 4.5 μg m⁻³ (0 °C, 760 mm Hg), respectively, whereas those of NO₃⁻, NH₄⁺, and DON in the rainwater within the study catchment were 1.3, 1.3, and 0.5 mg N L⁻¹, respectively. No clear difference in gaseous NO₂ concentrations and nitrogen concentrations in collected rainwater was found between the crop field and residential sites, but the average NH₃ concentration of 5.4 μg m⁻³ in residential sites was significantly higher than that in field sites (4.1 μg m⁻³). Total depositions were 40 kg N ha⁻¹ yr⁻¹ for crop field sites and 30 kg N ha⁻¹ yr⁻¹ for residential sites, in which dry depositions (NO₂ and NH₃) were 7.6 kg N ha⁻¹ yr⁻¹ for crop field sites and 1.9 kg N ha⁻¹ yr⁻¹ for residential sites. The DON in the rainwater accounted for 16% of the total wet nitrogen deposition. Oxidized N (NO₃⁻ in the precipitation and gaseous NO₂) was the dominant form of nitrogen deposition in the studied region, indicating that reactive forms of nitrogen created from urban areas contribute greatly to N deposition in the rural area evaluated in this study.     

Formation of bromoform in irradiated titanium dioxide suspensions with varying photocatalyst, dissolved organic carbon and bromide concentrations

We report the formation of bromoform in TiO₂ suspensions (P25) under simulated solar UV irradiation at different concentrations of photocatalyst (0.5-1.5 g L⁻¹) as well as initial concentrations of bromide ions (1-3 mg L⁻¹) and 2,4-dihydroxybenzoic acid (2-10 mg L⁻¹). The extent of bromoform formation (3-17 μg L⁻¹) was most strongly affected by the amount of photocatalyst present and by the initial bromide concentration, increasing either of which leads to increased bromoform formation. Important interaction effects were observed when simultaneously increasing the concentrations of TiO₂ and bromide as well as of bromide and DHBA. The time it takes for bromoform to appear in measurable concentrations in the irradiated TiO₂ suspensions was between 10 and 90 min and most strongly depended on the initial concentration of dissolved organic carbon present in the suspensions, along with the amount of photocatalyst, also in interaction with the initial bromide concentration.     

Precipitation of arsenic sulphide from acidic water in a fixed-film bioreactor

Arsenic (As) is a toxic element frequently present in acid mine waters and effluents. Precipitation of trivalent arsenic sulphide in sulphate-reducing conditions at low pH has been studied with the aim of removing this hazardous element in a waste product with high As content. To achieve this, a 400 mL fixed-film column bioreactor was fed continuously with a synthetic solution containing 100 mg L⁻¹ As(V), glycerol and/or hydrogen, at pH values between 2.7 and 5. The highest global As removal rate obtained during these experiments was close to 2.5 mg L⁻¹ h⁻¹. A switch from glycerol to hydrogen when the biofilm was mature induced an abrupt increase in the sulphate-reducing activity, resulting in a dramatic mobilisation of arsenic due to the formation of soluble thioarsenic complexes. A new analytical method, based on ionic chromatography, was used to evaluate the proportion of As present as thioarsenic complexes in the bioreactor. Profiles of pH, total As and sulphate concentrations suggest that As removal efficiency was linked to solubility of orpiment (As₂S₃) depending on pH conditions. Molecular fingerprints revealed fairly homogeneous bacterial colonisation throughout the reactor. The bacterial community was diverse and included fermenting bacteria and Desulfosporosinus-like sulphate-reducing bacteria. arrA genes, involved in dissimilatory reduction of As(V), were found and the retrieved sequences suggested that As(V) was reduced by a Desulfosporosinus-like organism. This study was the first to show that As can be removed by bioprecipitation of orpiment from acidic solution containing up to 100 mg L⁻¹ As(V) in a bioreactor.     

Speciation and distribution of vanadium in drinking water iron pipe corrosion by-products

Vanadium (V) when ingested from drinking water in high concentrations (> 15 μg L^− 1) is a potential health risk and is on track to becoming a regulated contaminant. High concentrations of V have been documented in lead corrosion by-products as Pb₅(V⁵⁺O₄)₃Cl (vanadinite) which, in natural deposits is associated with iron oxides/oxyhydroxides, phases common in iron pipe corrosion by-products. The extent of potential reservoirs of V in iron corrosion by-products, its speciation, and mechanism of inclusion however are unknown. The aim of this study is to assess these parameters in iron corrosion by-products, implementing synchrotron-based μ-XRF mapping and μ-XANES along with traditional physiochemical characterization. The morphologies, mineralogies, and chemistry of the samples studied are superficially similar to typical iron corrosion by-products. However, we found V present as discrete grains of Pb₅(V⁵⁺O₄)₃Cl likely embedded in the surface regions of the iron corrosion by-products. Concentrations of V observed in bulk XRF analysis ranged from 35 to 899 mg kg^− 1. We calculate that even in pipes with iron corrosion by-products with low V concentration, 100 mg kg^− 1, as little as 0.0027% of a 0.1-cm thick X 100-cm long section of that corrosion by-product needs to be disturbed to increase V concentrations in the drinking water at the tap to levels well above the 15 μg L^− 1 notification level set by the State of California and could adversely impact human health. In addition, it is likely that large reservoirs of V are associated with iron corrosion by-products in unlined cast iron mains and service branches in numerous drinking water distribution systems.     

Disinfection of Legionella pneumophila by ultrasonic treatment with TiO2

An ultrasonic treatment system, using a TiO₂ photocatalyst, was used to disinfect Legionella pneumophila. A kinetic study of the process indicates that TiO₂ significantly improves the disinfection process. The concentrations of viable cells were reduced to 6% of the initial concentrations in the presence of 0.2 g/ml TiO₂ after a 30 min of treatment period, while only an 18% reduction was observed in the absence of TiO₂. The potency of the disinfection could be enhanced, to some extent, by increasing the amount of TiO₂ used. Cell concentrations were decreased by an order of 3 within 30 min of treatment in the presence of 1.0 g/ml TiO₂. The disinfection power in the presence of TiO₂ versus Al₂O₃ was also compared and the findings showed that TiO₂ induced a higher cell killing. No significant effect of initial cell concentration on the disinfection was found in the range of 10²-10⁷ CFU/ml after a 30 min of treatment period. The mechanism of cell killing was investigated by examining the effects of OH radical scavengers such as ascorbic acid, histidine and glutathione. The disinfection power was reduced in samples that contained these radical scavengers, thus indicating the importance of OH radicals.     

Bacterial responses to Cu-doped TiO2 nanoparticles

The toxicity of Cu-doped TiO₂ nanoparticles (NPs, 20 nm), synthesized by a flame aerosol reactor, to Mycobacterium smegmatis and Shewanella oneidensis MR-1, is the primary focus of this study. Both doped and non-doped TiO₂ NPs (20 nm) tended to agglomerate in the medium solution, and therefore did not penetrate into the cell and damage cellular structures. TiO₂ particles (< 100 mg/L) did not apparently interfere with the growth of the two species in aqueous cultures. Cu-doped TiO₂ NPs (20 mg/L) significantly reduced the M. smegmatis growth rate by three fold, but did not affect S. oneidensis MR-1 growth. The toxicity of Cu-doped TiO₂ NPs was driven by the release of Cu²⁺ from the parent NPs. Compared to equivalent amounts of Cu²⁺, Cu-doped TiO₂ NPs exhibited higher levels of toxicity to M. smegmatis (P-value < 0.1). Addition of EDTA in the culture appeared to significantly decrease the anti-mycobacterium activity of Cu-doped TiO₂ NPs. S. oneidensis MR-1 produced a large amount of extracellular polymeric substances (EPS) under NP stress, especially extracellular protein. Therefore, S. oneidensis MR-1 was able to tolerate a much higher concentration of Cu²⁺ or Cu-doped TiO₂ NPs. S. oneidensis MR-1 also adsorbed NPs on cell surface and enzymatically reduced ionic copper in culture medium with a remediating rate of 61 µg/(liter?OD₆₀₀? hour) during its early exponential growth phase. Since the metal reducing Shewanella species can efficiently “clean” metal-oxide NPs, the activities of such environmentally relevant bacteria may be an important consideration for evaluating the ecological risk of metal-oxide NPs.     

Citizen monitoring: Testing hypotheses about the interactive influences of eutrophication and mussel invasion on a cyanobacterial toxin in lakes

An existing volunteer monitoring network in the state of Michigan was exploited to conduct a statewide survey of the cyanobacterial toxin, microcystin, and to test hypotheses about the interactive influences of eutrophication and dreissenid mussel invasion. A total of 77 lakes were sampled by citizen volunteers for microcystin, total phosphorus (TP) and chlorophyll a. Microcystin was measured in depth-integrated samples collected from the euphotic zone as well as in surface-water samples collected along the shoreline. Average microcystin in samples collected by volunteers was not different from samples collected side-by-side by professionals. Euphotic-zone microcystin was positively related to TP in lakes without dreissenids (uninvaded) but not in lakes with dreissenids (invaded). Regression-tree analysis indicated that euphotic-zone microcystin was eight times higher in the presence of dreissenids for lakes with TP between 5 and 10 μg L⁻¹. In contrast, euphotic-zone microcystin was almost identical in invaded and uninvaded lakes with TP between 10 and 26 μg L⁻¹. Across all lakes, microcystin concentrations at the surface were on average more than double, and in some cases an order-of-magnitude greater than, concentrations in the euphotic-zone. Given these results, it seems prudent to include dreissenid invasion status in forecasting models for microcystin, and to include shoreline sampling in monitoring programs aimed at assessing recreational exposure to cyanobacterial toxins.     

Degradation of the antibiotic oxolinic acid by photocatalysis with TiO2 in suspension

In the work presented here, a photocatalytic system using titanium Degussa P-25 in suspension was used to evaluate the degradation of 20 mg L⁻¹ of antibiotic oxolinic acid (OA). The effects of catalyst load (0.2-1.5 g L⁻¹) and pH (7.5-11) were evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, low pH values and 1.0 g L⁻¹ of TiO₂ favoured the efficiency of the process. Under optimal conditions the evolution of the substrate, chemical oxygen demand, dissolved organic carbon, toxicity and antimicrobial activity on Escherichia coli cultures were evaluated. The results indicate that, under optimal conditions, after 30 min, the TiO₂ photocatalytic system is able to eliminate both the substrate and the antimicrobial activity, and to reduce the toxicity of the solution by 60%. However, at the same time, ∼53% of both initial DOC and COD remain in solution. Thus, the photocatalytical system is able to transform the target compound into more oxidized by-products without antimicrobial activity and with a low toxicity. The study of OA by-products using liquid chromatography coupled with mass spectrometry, as well as the evaluation of OA degradation in acetonitrile media as solvent or in the presence of isopropanol and iodide suggest that the reaction is initiated by the photo-Kolbe reaction. Adsorption isotherm experiments in the dark indicated that under pH 7.5, adsorption corresponded to the Langmuir adsorption model, indicating the dependence of the reaction on an initial adsorption step.     

Investigating the potential role of ammonia in ion chemistry of fine particulate matter formation for an urban environment

To investigate the potential role of ammonia in ion chemistry of PM_2.5 aerosol, measurements of PM_2.5 (particulate matter having aerodynamic diameter < 2.5 µm) along with its ionic speciation and gaseous pollutants (sulfur dioxide (SO₂), nitrogen oxides (NO_x), ammonia (NH₃) and nitric acid (HNO₃)) were undertaken in two seasons (summer and winter) of 2007-2008 at four sampling sites in Kanpur, an urban-industrial city in the Ganga basin, India. Mean concentrations of water-soluble ions were observed in the following order (i) summer: SO₄²⁻ (26.3 µg m^− 3) > NO₃⁻ (16.8) > NH₄⁺ (15.1) > Ca²⁺ (4.1) > Na⁺ (2.4) > K⁺ (2.1 µg m^− 3) and (ii) winter: SO₄²⁻ (28.9 µg m^− 3) > NO₃⁻ (23.0) > NH₄⁺ (16.4) > Ca²⁺(3.4) > K⁺(3.3) > Na⁺ (3.2 µg m^− 3). The mean molar ratio of NH₄⁺ to SO₄²⁻ was 2.8 ± 0.6 (mostly >2), indicated abundance of NH₃ to neutralize H₂SO₄. The excess of NH₄⁺ was inferred to be associated with NO₃⁻ and Cl⁻. Higher sulfur conversion ratio (F_s: 58%) than nitrogen conversion ratio (F_n: 39%) indicated that SO₄²⁻ was the preferred secondary species to NO₃⁻. The charge balance for the ion chemistry of PM_2.5 revealed that compounds formed from ammonia as precursor are (NH₄)₂SO₄, NH₄NO₃ and NH₄Cl. This study conclusively established that while there are higher contributions of NH₄⁺, SO₄²⁻ to PM_2.5 in summer but for nitrates (in particulate phase), it is the winter season, which is critical because of low temperatures that drives the reaction between ammonia and HNO₃ in forward direction for enhanced nitrate formation. In summary, inorganic secondary aerosol formation accounted for 30% mass of PM_2.5 and any particulate control strategy should include optimal control of primary precursor gases including ammonia.     

Biodegradation of sulfamethazine by Trametes versicolor: Removal from sewage sludge and identification of intermediate products by UPLC-QqTOF-MS

Degradation of the sulfonamide sulfamethazine (SMZ) by the white-rot fungus Trametes versicolor was assessed. Elimination was achieved to nearly undetectable levels after 20 h in liquid medium when SMZ was added at 9 mg L^− 1. Experiments with purified laccase and laccase-mediators resulted in almost complete removal. On the other hand, inhibition of SMZ degradation was observed when piperonilbutoxide, a cytochrome P450-inhibitor, was added to the fungal cultures. UPLC-QqTOF-MS analysis allowed the identification and confirmation of 4 different SMZ degradation intermediates produced by fungal cultures or purified laccase: desulfo-SMZ, N⁴-formyl-SMZ, N⁴-hydroxy-SMZ and desamino-SMZ; nonetheless SMZ mineralization was not demonstrated with the isotopically labeled sulfamethazine-phenyl-¹³C₆ after 7 days. Inoculation of T. versicolor to sterilized sewage sludge in solid-phase systems showed complete elimination of SMZ and also of other sulfonamides (sulfapyridine, sulfathiazole) at real environmental concentrations, making this fungus an interesting candidate for further remediation research.     

Rhizosphere acidification of faba bean, soybean and maize

Interspecific facilitation on phosphorus uptake was observed in faba bean/maize intercropping systems in previous studies. The mechanism behind this, however, remained unknown. Under nitrate supply, the difference in rhizosphere acidification potential was studied by directly measuring pH of the solution and by visualizing and quantifying proton efflux of roots between faba bean (Vicia faba L. cv. Lincan No.5), soybean (Glycine max L. cv. Zhonghuang No. 17) and maize (Zea mays L. cv. Zhongdan No.2) in monoculture and intercrop, supplied without or with 0.2 mmol L^− 1 P as KH₂PO₄. The pH of the nutrient solution grown faba bean was lower than initial pH of 6.0 from day 1 to day 22 under P deficiency, whereas the pH of the solution with maize was declined from day 13 after treatment. Growing soybean increased solution pH irrespective of P supply. Under P deficiency, the proton efflux of faba bean both total (315.25 nmol h^− 1 plant^− 1) and specific proton efflux (0.47 nmol h^− 1 cm^− 1) was greater than that those of soybean (21.80 nmol h^− 1 plant^− 1 and 0.05 nmol h^− 1 cm^− 1, respectively). Faba bean had much more ability of rhizosphere acidification than soybean and maize. The result can explain partly why faba bean utilizes sparingly soluble P more effectively than soybean and maize do, and has an important implication in understanding the mechanism behind interspecific facilitation on P uptake by intercropped species.     

Temporal variation of nitro-polycyclic aromatic hydrocarbons in PM10 and PM2.5 collected in Northern Mexico City

With the aim to determine the presence of individual nitro-PAH contained in particles in the atmosphere of Mexico City, a monitoring campaign for particulate matter (PM₁₀ and PM_2.5) was carried out in Northern Mexico City, from April 2006 to February 2007. The PM₁₀ annual median concentration was 65.2 μg m^− 3 associated to 7.6 μg m^− 3 of solvent-extractable organic matter (SEOM) corresponding to 11.4% of the PM₁₀ concentration and 38.6 μg m^− 3 with 5.9 μg m^− 3 SEOM corresponding to 15.2% for PM_2.5. PM concentration and SEOM varied with the season and the particle size. The quantification of nitro-polycyclic aromatic hydrocarbons (nitro-PAH) was developed through the standards addition method under two schemes: reference standard with and without matrix, the former giving the best results. The recovery percentages varied with the extraction method within the 52 to 97% range depending on each nitro-PAH. The determination of the latter was effected with and without sample purification, also termed fractioning, giving similar results. 8 nitro-PAH were quantified, and their sum ranged from 111 to 819 pg m^− 3 for PM₁₀ and from 58 to 383 pg m^− 3 for PM_2.5, depending on the season. The greatest concentration was for 9-Nitroanthracene in PM₁₀ and PM_2.5, detected during the cold-dry season, with a median (10th-90th percentiles) concentration in 235 pg m^− 3 (66-449 pg m^− 3) for PM₁₀ and 73 pg m^− 3 (18-117 pg m^− 3) for PM_2.5. The correlation among mass concentrations of the nitro-PAH and criteria pollutants was statistically significant for some nitro-PAH with PM₁₀, SEOM in PM₁₀, SEOM in PM_2.5, NO_X, NO₂ and CO, suggesting either sources, primary or secondary origin. The measured concentrations of nitro-PAH were higher than those reported in other countries, but lower than those from Chinese cities. Knowledge of nitro-PAH atmospheric concentrations can aid during the surveillance of diseases (cardiovascular and cancer risk) associated with these exposures.     

Performance of a passive treatment system for net-acidic coal mine drainage over five years of operation

A full-scale passive treatment system (PTS) was commissioned in 2003 to treat two net-acidic coal mine water discharges in the Durham coalfield, UK. The principal aim of the PTS was to decrease concentrations of iron (< 177 mg L⁻¹) and aluminium (< 85 mg L⁻¹) and to increase pH (> 3.2) and alkalinity (≥ 0 mg L⁻¹ CaCO₃ eq). Secondary objectives were to decrease zinc (< 2.8 mg L⁻¹), manganese (< 20.5 mg L⁻¹) and sulfate (< 2120 mg L⁻¹). Upon treatment, water qualities were improved by 84% in the case of Fe, 87% Al, 83% acidity, 51% Zn, 23% Mn and 29% SO₄²⁻. Alkalinity (74%) and pH (95% as H⁺) were increased. Area adjusted removal rates (Fe = 1.49 ± 0.66 g d⁻¹ m⁻²; acidity = 6.7 ± 4.9 g d⁻¹ m⁻²) were low compared to design criteria, mainly due to load limitation. Disregarding seasonality effects, acidity removal and effluent pH were stable over time. A substantial temporal decrease in calcium and alkalinity generation suggests that limestone is increasingly armoured. Once pH is no longer buffered by the carbonate system, metals could be remobilized, putting treatment efficiency at risk.     

Photoassisted reduction of metal ions and organic dye by titanium dioxide nanoparticles in aqueous solution under anoxic conditions

The photoassisted reduction of metal ions and organic dye by metal-deposited Degussa P25 TiO₂ nanoparticles was investigated. Copper and silver ions were selected as the target metal ions to modify the surface properties of TiO₂ and to enhance the photocatalytic activity of TiO₂ towards methylene blue (MB) degradation. X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used to characterize the crystallinity, chemical species and morphology of metal-deposited TiO₂, respectively. Results showed that the particle size of metal-deposited TiO₂ was larger than that of Degussa P25 TiO₂. Based on XRPD patterns and XPS spectra, it was observed that the addition of formate promoted the photoreduction of metal ion by lowering its oxidation number, and subsequently enhancing the photodegradation efficiency and rate of MB. The pseudo-first-order rate constant (k_obs) for MB photodegradation by Degussa P25 TiO₂ was 3.94 × 10^− 2 min^− 1 and increased by 1.4-1.7 times in k_obs with metal-deposited TiO₂ for MB photodegradation compared to simple Degussa P25 TiO₂. The increase in mass loading of metal ions significantly enhanced the photodegradation efficiency of MB; the k_obs for MB degradation increased from 3.94 × 10^− 2 min^− 1 in the absence of metal ion to 4.64-7.28 × 10^− 2 min^− 1 for Ag/TiO₂ and to 5.14-7.61 × 10^− 2 min^− 1 for Cu/TiO₂. In addition, the electrons generated from TiO₂ can effectively reduce metal ions and MB simultaneously under anoxic conditions. However, metal ions and organic dye would compete for electrons from the illuminated TiO₂.     

Environmental impact of mining activities in the Lousal area (Portugal): chemical and diatom characterization of metal-contaminated stream sediments and surface water of Corona stream

Lousal mine is a typical “abandoned mine” with all sorts of problems as consequence of the cessation of the mining activity and lack of infrastructure maintenance. The mine is closed at present, but the heavy metal enriched tailings remain at the surface in oxidizing conditions. Surface water and stream sediments revealed much higher concentrations than the local geochemical background values, which the “Contaminated Sediment Standing Team” classifies as very toxic. High concentrations of Cu, Pb, Zn, As, Cd and Hg occurred within the stream sediments downstream of the tailings sites (up to: 817 mg kg⁻¹ As, 6.7 mg kg⁻¹ Cd, 1568 mg kg⁻¹ Cu, 1059 mg kg⁻¹ Pb, 82.4 mg kg⁻¹ Sb, 4373 mg kg⁻¹ Zn). The AMD waters showed values of pH ranging from 1.9 to 2.9 and concentrations of 9249 to 20,700 mg L⁻¹ SO₄⁻², 959 to 4830 mg L⁻¹ Fe and 136 to 624 mg L⁻¹ Al. Meanwhile, the acid effluents and mixed stream waters also carried high contents of SO₄^2−, Fe, Al, Cu, Pb, Zn, Cd, and As, generally exceeding the Fresh Water Aquatic Life Acute Criteria. Negative impacts in the diatom communities growing at different sites along a strong metal pollution gradient were shown through Canonical Correspondence Analysis: in the sites influenced by Acid Mine Drainage (AMD), the dominant taxon was Achnanthidium minutissimum. However, Pinnularia acoricola was the dominant species when the environmental conditions were extremely adverse: very low pH and high metal concentrations (sites 2 and 3). Teratological forms of Achnanthidium minutissimum (Kützing) Czarnecki, Brachysira vitrea (Grunow) Ross in Hartley, Fragilaria rumpens (Kützing) G. W. F. Carlson and Nitzschia hantzschiana Rabenhorst were found. A morphometric study of B. vitrea showed that a decrease in size was evident at the most contaminated sites. These results are evidence of metal and acidic pollution.