Erratum to “Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities”

The status of nitrate (NO₃⁻), nitrite (NO₂⁻) and ammonium (NH₄⁺) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate δ¹⁵N and δ¹⁸O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields).The exponential increase in NO₃⁻-δ¹⁵N along with the NO₃⁻ reduction and clear δ¹⁸O/δ¹⁵N slopes of NO₃⁻ (∼ 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO₃⁻ contamination via active denitrification and reduced nitrification.Our results showed that NO₃⁻ and NH₄⁺ contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Nitrate removal, communities of denitrifiers and adverse effects in different carbon substrates for use in denitrification beds

Denitrification beds are containers filled with wood by-products that serve as a carbon and energy source to denitrifiers, which reduce nitrate (NO₃⁻) from point source discharges into non-reactive dinitrogen (N₂) gas. This study investigates a range of alternative carbon sources and determines rates, mechanisms and factors controlling NO₃⁻ removal, denitrifying bacterial community, and the adverse effects of these substrates. Experimental barrels (0.2 m³) filled with either maize cobs, wheat straw, green waste, sawdust, pine woodchips or eucalyptus woodchips were incubated at 16.8 °C or 27.1 °C (outlet temperature), and received NO₃⁻ enriched water (14.38 mg N L⁻¹ and 17.15 mg N L⁻¹). After 2.5 years of incubation measurements were made of NO₃⁻-N removal rates, in vitro denitrification rates (DR), factors limiting denitrification (carbon and nitrate availability, dissolved oxygen, temperature, pH, and concentrations of NO₃⁻, nitrite and ammonia), copy number of nitrite reductase (nirS and nirK) and nitrous oxide reductase (nosZ) genes, and greenhouse gas production (dissolved nitrous oxide (N₂O) and methane), and carbon (TOC) loss. Microbial denitrification was the main mechanism for NO₃⁻-N removal. Nitrate-N removal rates ranged from 1.3 (pine woodchips) to 6.2 g N m⁻³ d⁻¹ (maize cobs), and were predominantly limited by C availability and temperature (Q₁₀ = 1.2) when NO₃⁻-N outlet concentrations remained above 1 mg L⁻¹. The NO₃⁻-N removal rate did not depend directly on substrate type, but on the quantity of microbially available carbon, which differed between carbon sources. The abundance of denitrifying genes (nirS, nirK and nosZ) was similar in replicate barrels under cold incubation, but varied substantially under warm incubation, and between substrates. Warm incubation enhanced growth of nirS containing bacteria and bacteria that lacked the nosZ gene, potentially explaining the greater N₂O emission in warmer environments. Maize cob substrate had the highest NO₃⁻-N removal rate, but adverse effects include TOC release, dissolved N₂O release and substantial carbon consumption by non-denitrifiers. Woodchips removed less than half of NO₃⁻ removed by maize cobs, but provided ideal conditions for denitrifying bacteria, and adverse effects were not observed. Therefore we recommend the combination of maize cobs and woodchips to enhance NO₃⁻ removal while minimizing adverse effects in denitrification beds.     

Plant tolerance to diesel minimizes its impact on soil microbial characteristics during rhizoremediation of diesel-contaminated soils

Soil contamination due to petroleum-derived products is an important environmental problem. We assessed the impacts of diesel oil on plants (Trifolium repens and Lolium perenne) and soil microbial community characteristics within the context of the rhizoremediation of contaminated soils. For this purpose, a diesel fuel spill on a grassland soil was simulated under pot conditions at a dose of 12,000 mg diesel kg^− 1 DW soil. Thirty days after diesel addition, T. repens (white clover) and L. perenne (perennial ryegrass) were sown in the pots and grown under greenhouse conditions (temperature 25/18 °C day/night, relative humidity 60/80% day/night and a photosynthetic photon flux density of 400 μmol photon m^− 2 s^− 1) for 5 months. A parallel set of unplanted pots was also included. Concentrations of n-alkanes in soil were determined as an indicator of diesel degradation. Seedling germination, plant growth, maximal photochemical efficiency of photosystem II (F_v/F_m), pigment composition and lipophylic antioxidant content were determined to assess the impacts of diesel on the studied plants. Soil microbial community characteristics, such as enzyme and community-level physiological profiles, were also determined and used to calculate the soil quality index (SQI). The presence of plants had a stimulatory effect on soil microbial activity. L. perenne was far more tolerant to diesel contamination than T. repens. Diesel contamination affected soil microbial characteristics, although its impact was less pronounced in the rhizosphere of L. perenne. Rhizoremediation with T. repens and L. perenne resulted in a similar reduction of total n-alkanes concentration. However, values of the soil microbial parameters and the SQI showed that the more tolerant species (L. perenne) was able to better maintain its rhizosphere characteristics when growing in diesel-contaminated soil, suggesting a better soil health. We concluded that plant tolerance is of crucial importance for the recovery of soil health during rhizoremediation of contaminated soils.     

Pollution of montane soil with Cu, Zn, As, Sb, Pb, and nitrate in Kanto, Japan

Soil cores and rainwater were sampled under canopies of Cryptomeria japonica in four montane areas along an atmospheric depositional gradient in Kanto, Japan. Soil cores (30 cm in depth) were divided into 2-cm or 4-cm segments for analysis. Vertical distributions of elemental enrichment ratios in soils were calculated as follows: (X/Al)_i/(X/Al)_BG (where the numerator and denominator are concentration ratios of element-X and Al in the i- and bottom segments of soil cores, respectively). The upper 14-cm soil layer showed higher levels of Cu, Zn, As, Sb, and Pb than the lower (14-30 cm) soil layer. In the four areas, the average enrichment ratios in the upper 6-cm soil layer were as follows: Pb (4.93) ≥ Sb (4.06) ≥ As (3.04) > Zn (1.71) ≥ Cu (1.56). Exogenous elements (kg/ha) accumulated in the upper 14-cm soil layer were as follows: Zn (26.0) > Pb (12.4) > Cu (4.48) ≥ As (3.43) ≥ Sb (0.49). These rank orders were consistent with those of elements in anthropogenic aerosols and polluted (roadside) air, respectively, indicating that air pollutants probably caused enrichment of these elements in the soil surface layer. Approximately half of the total concentrations of As, Sb, and Pb in the upper 14-cm soil layer were derived from exogenous (anthropogenic) sources. Sb showed the highest enrichment factor in anthropogenic aerosols, and shows similar deposition behavior to NO₃⁻, which is a typical acidic air pollutant. There was a strong correlation between Sb and NO₃⁻ concentrations in rainfall (e.g., in the throughfall under C. japonica: [NO₃⁻] = 21.1 [dissolved Sb], r = 0.938, p < 0.0001, n = 182). Using this correlation, total (cumulative) inputs of NO₃⁻ were estimated from the accumulated amounts of exogenous Sb in soils, i.e., 16.7 t/ha at Mt. Kinsyo (most polluted), 8.6 t/ha at Mt. Tsukuba (moderately polluted), and 5.8 t/ha at the Taga mountain system (least polluted). There are no visible ecological effects of these accumulated elements in the Kanto region at present. However, the concentrations of some elements are within a harmful range, according to the Ecological Soil Screening Levels determined by the U.S. Environmental Protection Agency.     

Whole lake selective withdrawal experiment to control harmful cyanobacteria in an urban impoundment

Different environmental conditions support optimal growth by Aphanizomenon and Microcystis in Ford Lake, Michigan, USA, based on weekly species biovolume and water chemistry measurements from June through October 2005-2007. Experimental withdrawal of hypolimnetic water through the outlet dam was conducted in 2006, with 2005 and 2007 acting as control years, to test theory regarding management of nuisance and toxic cyanobacteria. The dynamics of Aphanizomenon and Microcystis blooms in Ford Lake appear to be driven largely by NO₃⁻ concentrations, with higher levels shifting the advantage to Microcystis (P < 0.0001). Aphanizomenon was most successful with a mean TN:TP ratio (mol:mol) of 48.3:1, whereas Microcystis thrived with a mean ratio of 70.1:1. Withdrawal of hypolimnetic water successfully destabilized the water column and led to higher levels of NO₃⁻ and the near elimination of the Aphanizomenon bloom in 2006 (P < 0.0001). Selective withdrawal did not reduce Microcystis biovolume or microcystin toxicity. Microcystis biovolume and NO₃⁻ levels were positively correlated with microcystin toxin (P = 0.01) and jointly accounted for 30.5% of the variability in the data. Selective withdrawal may be a viable management option for improving water quality under certain circumstances. To fully address the problem of nuisance and toxic algal blooms in Ford Lake, however, an integrated approach is required that targets cyanobacteria biovolume dynamics as well as conditions suited for toxin production.     

Enhanced removal of polychlorinated biphenyls from alfalfa rhizosphere soil in a field study: The impact of a rhizobial inoculum

Polychlorinated biphenyls (PCB) are persistent pollutants in soil environments where they continue to present considerable human health risks. Successful strategies to remediate contaminated soils are needed that are effective and of low cost. Bioremediation approaches that include the use of plants and microbial communities to promote degradation of PCB have significant potential but need further assessment under field conditions. The effects of growth of alfalfa (Medicago sativa L.) and inoculation with a symbiotic nitrogen fixing bacterium (Rhizobium meliloti) on the removal of polychlorinated biphenyls (PCB) from rhizosphere soil were evaluated in a field experiment. The initial PCB content of the soil ranged from 414 to 498 µg kg⁻¹. PCB removal for the rhizosphere soil was enhanced in the planted treatments, an average of 36% decrease in PCB levels compared to a 5.4% decrease in the unplanted soil, and further enhanced when plants were inoculated with the symbiotic Rhizobium (an average of 43% decrease) when evaluated at 90 days after planting. Plant biomass production was higher in the inoculated treatment. The total PCB content was increased from 3.30 µg kg⁻¹ to 26.72 µg kg⁻¹ in plant shoots, and from 115.07 µg kg⁻¹ to 142.23 µg kg⁻¹ in roots in the inoculated treatment compared to the planted treatment. Increased colony forming units (cfu) of total heterotrophic bacteria, biphenyl-degrading bacteria and fungi were observed in the rhizosphere of inoculated plants. PCB removal from the rhizosphere soil was not significantly correlated with the direct PCB uptake by the plants in any of the treatments but was significantly correlated with the stimulation of rhizosphere microflora. Changes in the soil microbial community structure in the planted and inoculated treatment were observed by profiling of bacterial ribosomal sequences. Some bacteria, such as Flavobacterium sp., may have contributed to the effective degradation of PCB and deserve further investigation.     

The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008). Links were found between the dissolved organic carbon (DOC), nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy. Underlying soil type determined the leaching or accumulation of these elements. Under oak, monitored at two sites, frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of ~ 16 kg ha⁻¹extra N during defoliation. Peaks of nitrate (NO₃-N) flux between 5 and 9 kg ha⁻¹ (×5 usual winter values) were recorded in consecutive years in shallow soil waters. Synchronous rises in deep soil NO₃-N fluxes at the Grizedale sandy site indicate downward flushing, not seen at the clay site. Under three Sitka spruce stands, generation of honeydew (DOC) was attributed to two aphid species (Elatobium abietinum and Cinara pilicornis) with distinctive feeding strategies. Throughfall DOC showed mean annual fluxes (6 seasons) ~ 45-60 kg ha⁻¹ compared with rainfall values of 14-22 kg ha⁻¹. Increases of total N in throughfall and NO₃-N fluxes in shallow soil solution were detected — soil water fluxes reached  8 kg ha⁻¹ in Llyn Brianne, ~ 25 kg ha⁻¹ in Tummel, and ~ 40 kg NO₃-N ha⁻¹ in Coalburn. At Tummel, on sandy soil, NO₃-N leaching showed increased concentration at depth, attributed to microbiological activity within the soil. By contrast, at Coalburn and Llyn Brianne, sites on peaty gleys, soil water NO₃-N was retained mostly within the humus layer. Soil type is thus key to predicting N movement and retention patterns. These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems, on above and below ground processes affecting tree growth, soil condition, vegetation and water quality.     

Aerobic degradation of acid orange 7 in a vertical-flow constructed wetland

Biological, aerobic degradation of an azo dye and of the resultant, recalcitrant, aromatic amines in a constructed wetland (CW) was demonstrated for the first time. A vertical-flow CW, planted with Phragmites sp. was fed with 127 mg l⁻¹ of acid orange 7 (AO7) at hydraulic loads of 28, 40, 53 and 108 l m⁻²day⁻¹. Color removal efficiencies of up to 99% clearly demonstrate cleavage of the azo bond, also confirmed by the similar AO7 removal and SO₄²⁻ release rates revealing that adsorption onto the matrix was constant. The positive redox potential at the outlet demonstrates that aerobic conditions were present. Chemical oxygen demand and total organic carbon removal efficiencies of up to 93% were also indicative of AO7 mineralization. The degradation of sulfanilic acid was confirmed by the presence of NO₃⁻, SO₄²⁻ and secondary metabolites, which suggest at least two degradation pathways leading to a common compound, 3-oxoadipate.     

Identification and characterization of metabolic properties of bacterial populations recovered from arsenic contaminated ground water of North East India (Assam)

Diversity of culturable bacterial populations within the Arsenic (As) contaminated groundwater of North Eastern state (Assam) of India is studied. From nine As contaminated samples 89 bacterial strains are isolated. 16S rRNA gene sequence analysis reveals predominance of Brevundimonas (35%) and Acidovorax (23%) along with Acinetobacter (10%), Pseudomonas (9%) and relatively less abundant (<5%) Undibacterium, Herbaspirillum, Rhodococcus, Staphylococcus, Bosea, Bacillus, Ralstonia, Caulobacter and Rhizobiales members. High As(III) resistance (MTC 10–50 mM) is observed for the isolates obtained from As(III) enrichment, particularly for 3 isolates of genus Brevundimonas   (MTC 50 mM). In contrast, high resistance to As(V) (MTC as high as 550 mM) is present as a ubiquitous property, irrespective of isolates' enrichment condition. Bacterial genera affiliated to other groups showed relatively lower degree of As resistance [MTCs of 15–20 mM As(III) and 250–350 mM As(V)]. As(V) reductase activity is detected in strains with high As(V) as well as As(III) resistance. A strong correlation could be established among isolates capable of reductase activity and siderophore production as well as As(III) tolerance. A large number of isolates (nearly 50%) is capable of anaerobic respiration using alternate inorganic electron acceptors [As(V), Se(VI), Fe(III), ₃NO²⁻${{\text{NO}}_3}^{2\mathrm{-}}$, ₄SO²⁻${{\text{SO}}_4}^{2\mathrm{-}}$, S₂O₃²⁻${{\text{S}}_2{\text{O}}_3}^{2\mathrm{-}}$]. Ability to utilize different carbon sources ranging from C2–C6 compounds along with some complex sugars is also observed. Particularly, a number of strains is found to possess ability to grow chemolithotrophically using As(III) as the electron donor. The study reports for the first time the identity and metabolic abilities of bacteria in As contaminated ground water of North East India, useful to elucidate the microbial role in influencing mobilization of As in the region.     

Degradation of diclofenac by TiO2 photocatalysis: UV absorbance kinetics and process evaluation through a set of toxicity bioassays

In the present study the degradation kinetics and mineralization of diclofenac (DCF) by the TiO₂ photocatalysis were investigated in terms of UV absorbance and COD measurements for a wide range of initial DCF concentrations (5-80 mg L⁻¹) and photocatalyst loadings (0.2-1.6 g TiO₂ L⁻¹) in a batch reactor system. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Artemia salina) was performed to evaluate the potential detoxification of DCF. A pseudo-first-order kinetic model was found to fit well most of the experimental data, while at high initial DCF concentrations (40 and 80 mg L⁻¹) and at 1.6 g TiO₂ L⁻¹ photocatalyst loading a second-order kinetic model was found to fit the data better. The toxicity of the treated DCF samples on D. magna and P. subcapitata varied during the oxidation, probably due to the formation of some intermediate products more toxic than DCF. Unicellular freshwater algae was found to be very sensitive to the treated samples as well as the results from D. magna test were consistent to those of algae tests. A. salina was not found to be sensitive under the investigated conditions. Finally, UV absorbance analysis were found to be an useful tool for a fast and easy to perform measurement to get preliminary information on the organic intermediates that are formed during oxidation and also on their disappearance rate.     

Effects of wood ash fertilization on forest floor greenhouse gas emissions and tree growth in nutrient poor drained peatland forests

Wood ash (3.1, 3.3 or 6.6 tonnes dry weight ha^− 1) was used to fertilize two drained and forested peatland sites in southern Sweden. The sites were chosen to represent the Swedish peatlands that are most suitable for ash fertilization, with respect to stand growth response. The fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from the forest floor, measured using opaque static chambers, were monitored at both sites during 2004 and 2005 and at one of the sites during the period 1 October 2007-1 October 2008. No significant (p > 0.05) changes in forest floor greenhouse gas exchange were detected. The annual emissions of CO₂ from the sites varied between 6.4 and 15.4 tonnes ha^− 1, while the CH₄ fluxes varied between 1.9 and 12.5 kg ha^− 1. The emissions of N₂O were negligible. Ash fertilization increased soil pH at a depth of 0-0.05 m by up to 0.9 units (p < 0.01) at one site, 5 years after application, and by 0.4 units (p < 0.05) at the other site, 4 years after application. Over the first 5 years after fertilization, the mean annual tree stand basal area increment was significantly larger (p < 0.05) at the highest ash dose plots compared with control plots (0.64 m² ha^− 1 year^− 1 and 0.52 m² ha^− 1 year^− 1, respectively). The stand biomass, which was calculated using tree biomass functions, was not significantly affected by the ash treatment. The groundwater levels during the 2008 growing season were lower in the high ash dose plots than in the corresponding control plots (p < 0.05), indicating increased evapotranspiration as a result of increased tree growth. The larger basal area increment and the lowered groundwater levels in the high ash dose plots suggest that fertilization promoted tree growth, while not affecting greenhouse gas emissions.     

Experimental exploration on NO x diminution by the combined effect of antioxidant additives with SCR in a diesel engine powered by neem biodiesel

ABSTRACT

The use of biodiesel in diesel engines leads to the reduction of tail pipe emissions; But, several researchers portray that the use of biodiesel produces more NO_x pollution than diesel-fuelled engines, which is an hindrance for the scope of biodiesel usage. In this work, an experimental investigation of the combined effect of antioxidant additive added in the fuel as a fuel modification technique and SCR (selective catalytic reduction) as after a treatment technique on NO _x reduction in a neem biodiesel-powered compression ignition engine has been conducted. Results show that the antioxidant additive combined with the SCR technique reduces the NO _x emission significantly by 82% and there was a slight increase in UBHC and CO emission due to the addition of oxidation-suppressing additives with neem biodiesel and aqueous urea solution injection at the exhaust without a major drop in BTE and fuel consumption.     

The effects of Aphis fabae infestation on the antioxidant response and heavy metal content in field grown Philadelphus coronarius plants

The purpose of this study was to explore a possible relationship between the soil availability of metals and their concentrations in various parts of Philadelphuscoronarius plants. Moreover, the possible impact of an aphid infestation on the contamination and antioxidant response of plants from the urban environment of Kraków and the reference rural area of Zagaje Stradowskie (southern Poland) was analyzed. The contents of the glutathione, proline, non-protein − SH groups, antioxidants, and phosphorous and the levels of guaiacol peroxidase and catalase activity in leaves and shoots either infested or not by the aphid Aphis fabae Scop., were measured. The potential bioavailability of metals (Cd; Cu; Ni; Pb; Zn) in the soil and their concentrations in P. coronarius plants originating from both sites were compared.The antioxidant responses were generally elevated in the plants in the polluted area. Such reactions were additionally changed by aphid infestation. Generally, the concentrations of metals in the HNO₃ and CaCl₂ extractants of the soils from two layers at the 0-20 and 20-40 cm depths from the polluted area were higher than in those from the reference area. Such differences were found for nickel and lead (in all examined extractants), zinc (in soil extractants from the layer at 20-40 cm) and cadmium (in HNO₃ extractants). Significant positive relationships between the lead concentrations in the soil and in the plants were found. In the parts of plants from the polluted area, higher concentrations of Pb and Zn (leaves and shoots) and Cd (shoots) were recorded. The shoots and leaves of plants infested with aphids had higher concentrations of Zn but lower Pb. Moreover, their leaves had higher contaminations of Cu and Ni. In conclusion, aphids affected not only the antioxidant response of the plants but also their contamination with metals, especially contamination of the leaves.     

Influence of physicochemical and operational parameters on Nitrobacter and Nitrospira communities in an aerobic activated sludge bioreactor

To understand how to optimize performance of a partially nitrifying plant, the dynamics of Nitrospira and Nitrobacter abundance were studied over a 1 year period using quantitative polymerase chain reaction (qPCR) and their relative contributions to nitrite oxidation assessed including the affects of temperature and dissolved oxygen (DO). Correlation coefficients linking shifts in the community composition of nitrite-oxidizing bacteria (NOB) to operational or environmental variables indicated Nitrospira was significantly and negatively correlated to nitrite concentrations (r = −0.45, P < 0.01) and DO (r = −0.46, P < 0.01), while temperature showed a strong positive correlation (r = 0.59, P < 0.0001). However, the Nitrobacter portion of the total NOB populations showed a positive correlations with DO (r = 0.38, P < 0.01) and hydraulic retention time (HRT) (r = 0.33, P < 0.05), as well as being negatively correlated with temperature (r = −0.49, P < 0.001) suggesting specific niche adaptations within the NOB community. Nitrospira was dominant being better adapted to the low DO and shorter sludge retention times (SRT) of this plant, while Nitrobacter increased in abundance during the winter months, when temperatures were lower and DO concentrations higher. Principal component analysis (PCA) results supported these findings by the close proximity of Nitrospira and temperature biplots of PC1 and PC2 as well as grouping Nitrobacter, NO₂⁻-N, HRT, and DO in the loadings together. The clustering of samples from specific dates also exhibited a strong seasonality.     

Nitrate and fluoride contamination in groundwater of an intensively managed agroecosystem: A functional relationship

A study was conducted to assess the potential of nitrate-nitrogen (NO₃-N) and fluoride (F) contamination in drinking groundwater as a function of lithology, soil characteristics and agricultural activities in an intensively cultivated district in India. Two hundred and fifty two groundwater samples were collected at different depths from various types of wells and analyzed for pH, electrical conductivity (EC), NO₃-N load and F content. Database on lithology, soil properties, predominant cropping systems, fertilizer and pesticide uses were also recorded for the district. The NO₃-N load in groundwater samples were low ranging from 0.12 to 6.58 μg mL^− 1 with only 8.7% of them contained greater than 3.0 μg mL^− 1 well below the 10 μg mL^− 1, the threshold limit fixed by WHO for drinking purpose. Samples from the habitational areas showed higher NO₃-N content over the agricultural fields. The content decreased with increasing depth of wells (r = − 0.25, P ≤ 0.01) and increased with increasing rate of nitrogenous fertilizer application (r = 0.90, P ≤ 0.01) and was higher in areas where shallow- rather than deep-rooted crops (r = − 0.28, P = ≤ 0.01, with average root depth) are grown. The NO₃-N load also decreased with increasing bulk density (r = − 0.73, P ≤ 0.01) and clay content (r = − 0.51, P ≤ 0.01) but increased with increasing hydraulic conductivity (r = 0.68, P ≤ 0.01), organic C (r = 0.78, P ≤ 0.01) and potential plant available N (r = 0.82, P ≤ 0.01) of soils. Fluoride content in groundwater was also low (0.02 to 1.15 μg mL^− 1) with only 4.0% of them exceeding 1.0 μg mL^− 1 posing a potential threat of fluorosis. On average, its content varied little spatially and along depth of sampling aquifers indicating little occurrence of F containing rocks/minerals in the geology of the district. The content showed a significant positive correlation (r = 0.234, P = ≤ 0.01) with the amount of phosphatic fertilizer (single super phosphate) used for agriculture. Results thus indicated that the groundwater of the study area is presently safe for drinking purpose but some anthropogenic activities associated with intensive cultivation had a positive influence on its loading with NO₃-N and F.     

Determination of sorption of seventy-five pharmaceuticals in sewage sludge

Sorption of 75 active pharmaceutical ingredients (APIs) to three different types of sludge (primary sludge, secondary sludge with short and long sludge age respectively) were investigated. To obtain the sorption isotherms batch studies with the APIs mixture were performed in four nominal concentrations to water containing 1 g of sludge. The range of APIs concentrations was between ng L⁻¹ to μg L⁻¹ which are found in the wastewater effluents. Isotherms were obtained for approximately 45 of the APIs, providing distribution coefficients for linear (K_d), Freundlich (K_f) and Langmuir (K_L) isotherms. K_d, K_f and K_L ranging between 7.1 × 10⁴ and 3.8 × 10⁷, 1.1 × 10⁻² and 6.1 × 10⁴ and 9.2 × 10⁻³ and 1.1 L kg⁻¹, respectively. The obtained coefficients were applied to estimate the fraction of APIs in the water phase (see Abstract Graphic). For 37 of the 75 APIs, the predicted presence in the liquid phase was estimated to >80%. 24 APIs were estimated to be present in the liquid phase between 20 and 80%, and 14 APIs were found to have <20% presence in the liquid phase, i.e. high affinity towards sludge. Furthermore, the effect of pH at values 6, 7 and 8 was evaluated using one way ANOVA-test. A significant difference in K_ds due to pH changes were found for 6 of the APIs (variation 10-20%).     

Present limitations and future prospects of stable isotope methods for nitrate source identification in surface- and groundwater

Nitrate (NO₃⁻) contamination of surface- and groundwater is an environmental problem in many regions of the world with intensive agriculture and high population densities. Knowledge of the sources of NO₃⁻ contamination in water is important for better management of water quality. Stable nitrogen (δ¹⁵N) and oxygen (δ¹⁸O) isotope data of NO₃⁻ have been frequently used to identify NO₃⁻ sources in water. This review summarizes typical δ¹⁵N- and δ¹⁸O-NO₃⁻ ranges of known NO₃⁻ sources, interprets constraints and future outlooks to quantify NO₃⁻ sources, and describes three analytical techniques (“ion-exchange method”, “bacterial denitrification method”, and “cadmium reduction method”) for δ¹⁵N- and δ¹⁸O-NO₃⁻ determination. Isotopic data can provide evidence for the presence of dominant NO₃⁻ sources. However, quantification, including uncertainty assessment, is lacking when multiple NO₃⁻ sources are present. Moreover, fractionation processes are often ignored, but may largely constrain the accuracy of NO₃⁻ source identification. These problems can be overcome if (1) NO₃⁻ isotopic data are combined with co-migrating discriminators of NO₃⁻ sources (e.g. ¹¹B), which are not affected by transformation processes, (2) contributions of different NO₃⁻ sources can be quantified via linear mixing models (e.g. SIAR), and (3) precise, accurate and high throughput isotope analytical techniques become available.     

Iron amendment and Fenton oxidation of MTBE-spent granular activated carbon

Fenton-driven regeneration of methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) involves an Fe amendment step to increase the Fe content and to enhance the extent of MTBE oxidation and GAC regeneration. Four forms of iron (ferric sulfate, ferric chloride, ferric nitrate, ferrous sulfate) were amended separately to GAC. Following Fe amendment, MTBE was adsorbed to the GAC followed by multiple applications of H₂O₂. Fe retention in GAC was high (83.8-99.9%) and decreased in the following order, FeSO₄·7H₂O > Fe₂(SO₄)₃·9H₂O > Fe(NO₃)₃·9H₂O > FeCl₃. A correlation was established between the post-sorption aqueous MTBE concentrations and Fe on the GAC for all forms of Fe investigated indicating that Fe amendment interfered with MTBE adsorption. However, the mass of MTBE adsorbed to the GAC was minimally affected by Fe loading. Relative to ferric iron amendments to GAC, ferrous iron amendment resulted in lower residual iron in solution, greater Fe immobilization in the GAC, and less interference with MTBE adsorption. MTBE oxidation was Fe limited and no clear trend was established between the counter-ion (SO₄²⁻, Cl⁻, NO₃⁻) of the ferric Fe amended to GAC and H₂O₂ reaction, MTBE adsorption, or MTBE oxidation, suggesting these processes are anion independent.     

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.     

Emission of CO2 and N2O from soil cultivated with common bean (Phaseolus vulgaris L.) fertilized with different N sources

Addition of different forms of nitrogen fertilizer to cultivated soil is known to affect carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions. In this study, the effect of urea, wastewater sludge and vermicompost on emissions of CO₂ and N₂O in soil cultivated with bean was investigated. Beans were cultivated in the greenhouse in three consecutive experiments, fertilized with or without wastewater sludge at two application rates (33 and 55 Mg fresh wastewater sludge ha^− 1, i.e. 48 and 80 kg N ha^− 1 considering a N mineralization rate of 40%), vermicompost derived from the wastewater sludge (212 Mg ha^− 1, i.e. 80 kg N ha^− 1) or urea (170 kg ha^− 1, i.e. 80 kg N ha^− 1), while pH, electrolytic conductivity (EC), inorganic nitrogen and CO₂ and N₂O emissions were monitored. Vermicompost added to soil increased EC at onset of the experiment, but thereafter values were similar to the other treatments. Most of the NO₃⁻ was taken up by the plants, although some was leached from the upper to the lower soil layer. CO₂ emission was 375 C kg ha^− 1 y^− 1 in the unamended soil, 340 kg C ha^− 1 y^− 1 in the urea-amended soil and 839 kg ha^− 1 y^− 1 in the vermicompost-amended soil. N₂O emission was 2.92 kg N ha^− 1 y^− 1 in soil amended with 55 Mg wastewater sludge ha^− 1, but only 0.03 kg N ha^− 1 y^− 1 in the unamended soil. The emission of CO₂ was affected by the phenological stage of the plant while organic fertilizer increased the CO₂ and N₂O emission, and the yield per plant. Environmental and economic implications must to be considered to decide how many, how often and what kind of organic fertilizer could be used to increase yields, while limiting soil deterioration and greenhouse gas emissions.