High Nitrite Concentrations Research Articles

Characteristics of nitrogen transformation and intracellular nitrite accumulation by the hypothermia bacterium Arthrobacter arilaitensis

A new nitrite accumulation pathway was discovered in the nitrogen conversion process of Arthrobacter arilaitensis. The extracellular nitrite reached 0.65 and 43.66 mg/L with hydroxylamine and nitrate as the sole nitrogen source, respectively. The enzyme activities of ammonia monooxygenase, hydroxylamine oxidoreductase and nitrate reductase were 0.42, 0.0014 and 0.0049 U/mg protein, respectively. The activity of nitrite reductase was completely inhibited by diethyldithiocarbamate. Intriguingly, the intracellular nitrite accumulated as high as 43.0, 42.26, 39.94 and 35.01 mg/L, when the Arthrobacter arilaitensis was incubated with Luria-Bertani medium, ammonium, nitrate and nitrite as the nitrogen source, respectively. These results confirmed that the highest concentration of intracellular nitrite was accumulated when LB was selected as the nitrogen source, followed by ammonium and nitrate, then nitrite was the least. To date, biochemical mechanism responsible for the accumulation of a high concentration of intracellular nitrite is unknown.

Is Pseudanodonta complanata the most vulnerable of widespread European species of unionids? An intense stress test leading to a massive die‐off

Abstract This article reports a large‐scale die‐off of approximately one‐third of the unionid mussels inhabiting a shallow, naturally eutrophic, floodplain lake (Zalew Pińczowski), which took place within the space of just a few days. Mortality was the highest in Pseudanodonta complanata (81%), followed by Unio pictorum (58%), Anodonta cygnea (26%), Unio tumidus (15%), and Anodonta anatina (5%). It was significantly related to mussel size (age) only in A. cygnea, with the mortality rate higher in smaller (young) mussels. Pseudanodonta complanata was already the rarest species in the lake, and the number of survivors decreased to such an extent as to trigger a possible Allee effect. The most likely cause of the die‐off was a motor‐boating incident that had directly preceded the die‐off. Analysis of the water samples collected just after the die‐off revealed an extremely high concentration of phosphate (up to 0.5 mg dm−3) and nitrite (up to 0.06 mg dm−3). We suggest that the boat movements must have disturbed the lake sediments, thereby disrupting the mussels' physiology and causing mass mortality. The high sensitivity of P. complanata to environmental stress suggests that it may be an effective umbrella species for the protection of co‐occurring mussel species in eutrophic lakes.

Exposure to nitrite alters thyroid hormone levels and morphology in Takifugu rubripes

Nitrite (NO2−) can act as a toxic nitrogenous compound with the potential to disrupt endocrine systems in fish. The aim of the present study was to investigate the effects of nitrite on the thyroid endocrine system of Takifugu rubripes. Fish were exposed to 0, 0.5, 1, 3, and 6 mM nitrite concentrations. Blood was collected to assay the concentrations of thyroid-stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3), free thyroxine (FT4), free triiodothyronine (FT3), and 3,3,5′-triiodothyronine (rT3), as well as the activity of iodothyronine deiodinases (Dio1, Dio2, and Dio3,) after 0, 12, 24, 48, and 96 h of exposure to nitrite. The first branchial arch to the third branchial arch of T. rubripes were sampled and fixed, and thyroid morphology was observed. The results showed that exposure to nitrite significantly increased the concentrations of TSH, T3, FT3, and reduced the concentrations of T4, FT4, and rT3. The activity of Dio1 and Dio2 increased significantly, whereas Dio3 activity decreased significantly. Additionally, thyroid follicles degenerated and became blurred and most colloid material disappeared 96 h after exposure to high nitrite concentrations. Based on these results, high nitrite concentration exposure can disturb thyroid hormone homeostasis, alter thyroid follicle morphology, and result in thyroid endocrine toxicity.

Individual and combined effect of salinity and nitrite on freshwater Anammox bacteria (FAB)

Anaerobic ammonium oxidation (Anammox) based technology has potential for nitrogen removal from wastewater with high salinity, but both salt and nitrite (a substrate for Anammox) have negative effect on microbial activity. In order to achieve Anammox in saline wastewater treatment, it is essential to understand the combined effect of these two components. In this study, the individual and combined effect of salinity and nitrite on fixed film freshwater Anammox bacteria (FAB, mainly belonging to the Ca. Brocadia genus), enriched on carriers from a 1500 L pilot scale one-stage (PN/Anammox) moving bed bioreactor (MBBR), were systematically investigated by 57 pre-designed batch tests. The combined inhibition of nitrite and salinity was determined by comparing with additive and independent inhibition models. With salinity only, the specific Anammox activity (SAA) decreased with increasing salinity: 14.6 mS/cm (about 9.1 g NaCl/L) of salinity caused 50% inhibition (IC50). With nitrite only, SAA started to decrease when nitrite concentration was above 450 mg N/L (threshold) and decreased with increased nitrite (IC50 = 666 mg N/L) thereafter. Significantly, when both salinity and nitrite were elevated, both the threshold and IC50 of nitrite were reduced, with inhibition enhanced. Analysis showed that at high salinity (>14.6 mS/cm) and nitrite concentration (>666 mg N/L), inhibition was close to that predicted by simulation of additive and independent inhibition models. Within a salinity range of 4–14.6 mS/cm and nitrite concentration range of 50–666 mg N/L, the combined inhibition was more severe than prediction (p < 0.05) based on the additive and independent inhibition models and therefore it was determined to be synergistic inhibition.

Modelling N2O dynamics of activated sludge biomass: Uncertainty analysis and pathway contributions

Nitrous oxide (N2O) is a potent greenhouse gas emitted during biological wastewater treatment. A pseudo-mechanistic model describing three biological pathways for nitric oxide (NO) and N2O production was calibrated for mixed culture biomass from an activated sludge process using laboratory-scale experiments.The model (NDHA) comprehensively describes N2O producing pathways by both autotrophic ammonium oxidizing bacteria and heterotrophic bacteria. Extant respirometric assays and anaerobic batch experiments were designed to calibrate endogenous and exogenous processes (heterotrophic denitrification and autotrophic ammonium/nitrite oxidation) together with the associated net N2O production. Ten parameters describing heterotrophic processes and seven for autotrophic processes were accurately estimated (variance/mean < 25%). The model predicted accurately NO and N2O dynamics at varying dissolved oxygen, ammonium and nitrite levels, and was validated against an independent set of experiments with the same biomass.In aerobic ammonium oxidation experiments the nitrifier denitrification and heterotrophic denitrification estimated pathway contributions increased at high nitrite and low oxygen concentrations; while the nitrifier nitrification pathway showed the largest contribution at high dissolved oxygen levels. The uncertainty of N2O emissions during model calibration is commonly overlooked, which limits the confidence of model-based mitigation strategies. Here we show that the precision of the estimated parameters resulted in a low uncertainty of the N2O emission factors during aerobic ammonium oxidation at DO ≈ 2.0 mg/L (1.2 ± 0.1%) and DO ≈ 0.5 mg/L (4.6 ± 0.6%).

Exposure time relevance of response to nitrite exposure: Insight from transcriptional responses of immune and antioxidant defense in the crayfish, Procambarus clarkii

To understand the toxic effects of nitrite exposure on crayfish, expression of genes involved in the immune system, the antioxidant defense, and the heat shock protein 70 (HSP70) was measured after 12, 24, and 48 h of different nitrite concentrations exposure in the hepatopancreas and hemocytes of Procambarus clarkii. Nitrite exposure up-regulated mRNA levels of cytoplasmic Mn superoxide dismutase (cMn-SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione-S-transferase (GST), after 24 h nitrite exposure. At 48 h, nitrite exposure decreased the mRNA levels of mitochondrial MnSOD (mMn-SOD), CAT, and GPx. High concentrations of nitrite at 48 h of exposure decreased expression of β-1,3-glucan-bingding protein in the hepatopancreas, and lysozyme expression in hemocytes. Nitrite exposure caused little effect on the heat shock protein 70 (HSP70) in hemocytes. Through overall clustering analysis, we found that 24 h of nitrite exposure caused stronger transcriptional responses. Our study indicated that the response of P. clarkii to acute nitrite exposure was exposure time-dependent. These results will help to understand the dynamic response pattern of crustaceans to nitrite pollution, and improve our understanding of the toxicological mechanisms of nitrite in crustaceans.

Effects of chronic sub‐lethal nitrite exposure at high water chloride concentration on Atlantic salmon ( Salmo salar, Linnaeus 1758) parr

The present study examined the protective effects of water chloride (Cl−) towards nitrite toxicity in Atlantic salmon parr during 84-day long nitrite exposure. Effects on growth, histology, blood indices and gene expression were studied at a fixed nominal Cl− concentration of 200 mg/L and at several water nitrite concentrations (0, 0.5, 2, 5 and 10 mg/L NO2−–N). The specific growth rate was significantly reduced during the first three weeks at a Cl:NO2−–N ratio of 21:1, suggesting the activation of coping mechanisms at the later stages of the experiment. No significant effect of nitrite on gill histology and mortality was found. Nitrite accumulated in plasma; however, a Cl:NO2−–N ratio of 104:1 or higher prevented nitrite entry. The concentration of NO2−–N in plasma was significantly reduced at the end of the study, supporting the hypothesis of coping mechanisms. Cystic fibrosis transmembrane conductance regulator (cftr)-1 showed a significant up-regulation at highest nitrite concentration on day 22, and in three of the highest exposure groups at the end of the experiment. Our findings suggest that a Cl:NO2−–N ratio above 104:1 should be maintained through episodes of nitrite accumulation in water during the production of Atlantic salmon parr.

Dietary Nitrite Drives Disease Outcomes in Oral Polymicrobial Infections

Streptococcus mutans resides in the oral polymicrobial biofilm and is a major contributor to the development of dental caries. Interestingly, high salivary nitrite concentrations have been associated with a decreased prevalence of dental caries. Moreover, the combination of hydrogen peroxide–producing oral commensal streptococci and nitrite has been shown to mediate the generation of reactive nitrogen species, which have antimicrobial activity. The goal of this study was to examine whether nitrite affects S. mutans virulence during polymicrobial infections with the commensal Streptococcus parasanguinis. Here, we report that the combination of S. parasanguinis and nitrite inhibited S. mutans growth and biofilm formation in vitro. Glucan production, which is critical for S. mutans biofilm formation, was also inhibited in 2-species biofilms with S. parasanguinis containing nitrite as compared with biofilms that contained no nitrite. In the in vivo caries model, enamel and dentin carious lesions were significantly reduced in rats that were colonized with S. parasanguinis prior to infection with S. mutans and received nitrite in the drinking water, as compared with animals that had a single S. mutans infection or were co-colonized with both bacteria and received no nitrite. Last, we report that S. mutans LiaS, a sensor kinase of the LiaFSR 3-component system, mediates resistance to nitrosative stress. In summary, our data demonstrate that commensal streptococci and nitrite provide protection against S. mutans pathogenesis. Modulating nitrite concentrations in the oral cavity could be a useful strategy to combat the prevalence of dental caries.

Abiotic and biotic processes of diclofenac in enriched nitrifying sludge: Kinetics, transformation products and reactions

Diclofenac (DCF), as an emerging contaminant in aquatic environments, has sparked increasing concerns about its impact on the environment. Nitrification in wastewater treatment processing has removed DCF to a large extent. However, the removal characteristics and mechanisms of DCF in the nitrification process are still poorly understood. In this study, enriched nitrifying sludge was used to investigate the transformation of DCF during the nitrification process. Elimination of DCF caused by volatilization, hydrolyzation and adsorption was limited. Abiotic nitration removal was confirmed as significant in enriched nitrifying sludge at a low pH and high nitrite concentration. Free nitrite acid was proposed as the reaction species participating in the DCF transformation process, and a regression equation was developed to predict the contribution of abiotic nitration on DCF removal in enriched nitrifying sludge. By slowly and continuously adding an ammonia stock solution and controlling the pH, we avoided the effect of abiotic nitration removal, and DCF biodegradation was positively correlated to specific ammonium oxidation rates (SAORs). The removal of DCF fit the first order kinetic model (R2 = 0.8285, p < 0.05) with an SAOR of 0.25 mg NH4+-N/(gMLSS·min). The high removal rate constant of k (0.1286 L/(gMLSS·h)) and short half-life (2.48 h) revealed the strong capability of nitrifying bacteria to transform DCF. Nine DCF transformation products were identified and three of them were quantified in the transformation process. The formation of kinetic profile 4-OH-DCF, 5-OH-DCF and DCF-Benzoic acid (DCF-BA) implied that hydroxylation may be the first reaction of DCF and DCF-BA may be a terminal product that resists further degradation. The postulated reactions concerning the transformation of DCF were hydroxylation, lactam formation and oxidation. Accordingly, a detailed degradation pathway was presented.

The Role of Reactive Nitrogen Species in Sensitized Photolysis of Wastewater-Derived Trace Organic Contaminants.

Under conditions typically encountered in the aquatic environment, the absorption of sunlight by nitrite and nitrate leads to the transformation of trace organic contaminants. In addition to the well understood mechanism through which hydroxyl radical (·OH) produced by nitrate and nitrite photolysis oxidizes contaminants, absorption of light also results in the formation of reactive nitrogen species that transform organic contaminants. To assess the importance of this process on the fate of trace organic contaminants, radical quenchers and transformation product analysis were used to discriminate among potential reaction pathways. For sulfamethoxazole, an antibiotic that is frequently detected in municipal wastewater effluent, nitrate and nitrite-sensitized photolysis pathways resulted in production of transformation products that were not detected during direct photolysis or reaction with ·OH. The reactivity of sulfamethoxazole with the reactive species produced when nitrite absorbed sunlight was affected by the presence of hydroxyl radical scavengers, indicating the likely involvement of nitrogen dioxide, which forms when nitrite reacts with hydroxyl radical. Reactive nitrogen species also reacted with emtricitabine, propranolol, and other trace organic contaminants commonly detected in wastewater effluent, indicating the potential importance of this process to the fate of other trace organic contaminants. A kinetic model indicated that reactive nitrogen species could be important to the phototransformation of trace organic contaminants when relatively high concentrations of nitrite are present (e.g., in surface waters receiving reverse osmosis concentrate from potable water reuse projects or in agricultural runoff).

Dietary intake of inorganic nitrate in vegetarians and omnivores and its impact on blood pressure, resting metabolic rate and the oral microbiome

Vegetarian diets are commonly associated with lower blood pressure levels. This has been related to greater consumption of inorganic nitrate, since vegetables are the main source of this anion. Dietary nitrate is reduced to nitrite by commensal bacteria in the mouth, which in turn leads to increased circulatory nitrite availability. Nitrite can form nitric oxide by several pathways promoting a reduction in the vascular tone and lower blood pressure. This study tested whether vegetarians have higher concentrations of nitrite in saliva and plasma, and lower blood pressure and resting metabolic rate (RMR), due to higher intakes of nitrate, compared to omnivores. Following a non-randomized, cross-over and single-blinded design we measured dietary nitrate intake, blood pressure and RMR in young and healthy vegetarians (n = 22) and omnivores (n = 19) with similar characteristics after using placebo or antibacterial mouthwash for a week to inhibit oral bacteria. Additionally, we analyzed salivary and plasma nitrate and nitrite concentrations, as well as the oral nitrate-reduction rate and oral microbiome in both groups. Dietary nitrate intake in vegetarians (97 ± 79 mg/day) was not statistically different (P > 0.05) to omnivores (78 ± 47 mg/day). Salivary and plasma nitrate and nitrite concentrations were similar after placebo mouthwash in both groups (P > 0.05). The oral nitrate-reducing capacity, abundance of oral bacterial species, blood pressure and RMR were also similar between vegetarians and omnivores (P > 0.05). Antibacterial mouthwash significantly decreased abundance of oral nitrate-reducing bacterial species in vegetarians (_16.9%; P < 0.001) and omnivores (_17.4%; P < 0.001), which in turn led to a significant reduction of the oral nitrate-reducing capacity in vegetarians (−78%; P < 0.001) and omnivores (−85%; P < 0.001). However, this did not lead to a significant increase in blood pressure and RMR in either groups (P > 0.05). These findings suggest that vegetarian diets may not alter nitrate and nitrite homeostasis, or the oral microbiome, compared to an omnivore diet. Additionally, inhibition of oral nitrite synthesis for a week with antibacterial mouthwash did not cause a significant raise in blood pressure and RMR in healthy, young individuals independent of diet.

A Physiological and Genomic Comparison of Nitrosomonas Cluster 6a and 7 Ammonia-Oxidizing Bacteria.

Ammonia-oxidizing bacteria (AOB) within the genus Nitrosomonas perform the first step in nitrification, ammonia oxidation, and are found in diverse aquatic and terrestrial environments. Nitrosomonas AOB were grouped into six defined clusters, which correlate with physiological characteristics that contribute to adaptations to a variety of abiotic environmental factors. A fundamental physiological trait differentiating Nitrosomonas AOB is the adaptation to either low (cluster 6a) or high (cluster 7) ammonium concentrations. Here, we present physiological growth studies and genome analysis of Nitrosomonas cluster 6a and 7 AOB. Cluster 6a AOB displayed maximum growth rates at ≤ 1mM ammonium, while cluster 7 AOB had maximum growth rates at ≥ 5mM ammonium. In addition, cluster 7 AOB were more tolerant of high initial ammonium and nitrite concentrations than cluster 6a AOB. Cluster 6a AOB were completely inhibited by an initial nitrite concentration of 5mM. Genomic comparisons were used to link genomic traits to observed physiological adaptations. Cluster 7 AOB encode a suite of genes related to nitrogen oxide detoxification and multiple terminal oxidases, which are absent in cluster 6a AOB. Cluster 6a AOB possess two distinct forms of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and select species encode genes for hydrogen or urea utilization. Several, but not all, cluster 6a AOB can utilize urea as a source of ammonium. Hence, although Nitrosomonas cluster 6a and 7 AOB have the capacity to fulfill the same functional role in microbial communities, i.e., ammonia oxidation, differentiating species-specific and cluster-conserved adaptations is crucial in understanding how AOB community succession can affect overall ecosystem function.

NO and N2O accumulation during nitrite-based sulfide-oxidizing autotrophic denitrification

A series of batch tests were carried out in a nitrite-based Sulfide-oxidizing autotrophic denitrification (SOAD) lab-scale sequencing biofilm batch reactor under four different influent conditions. Results indicated that the two stages of sulfide oxidized to S0 and S0 oxidized to SO42− proceed successively and could be distinguished by pH variation. The dissolved nitrous oxide (N2O) and nitric oxide (NO) monitored online were observed accumulating at the beginning of every new cycle once nitrite and sulfide were fed in pulse. Along with the NO accumulation dissolved oxygen (DO) level increased, accidentally, although the reactor was sealed and no aeration. The high nitrite concentration caused the NO accumulation which could be promoted by the low ratio of S/N. N2O accumulation resulted from the double inhibitions of sulfide and FNA. Thiobacillus, Ottowia, Thiovirga presented the functional genera to remove sulfide and nitrite in this study.

Nitrite Disruption in Olfaction and Internal Physiology in Goldfish (Carassius auratus)

Freshwater ecosystems have experienced a dramatic increase of nitrogenous compounds as a result of farming and industrial activity. Nitrite accumulates by bacterial denitrification/nitrification in freshwater and saltwater ecosystems, reaching concentrations of 1 mM and 0.5 μM respectively. Exposure to high nitrite concentrations can disrupt the endocrine system and physiological processes such as ion homeostasis, respiratory, and cardiovascular activity. However, the accumulation of nitrite in different internal tissues and its effect on external sensitive organs, such as the olfactory epithelium, is unknown. This study aimed to determine the physiological effects of nitrite and its accumulation in several organs in goldfish (Carassius auratus). Goldfish were exposed to different nitrite treatments (0 mM, 0.3 mM, 1.0 mM, and 10 mM) for five days. Upon completion of experiment, brain, nose, liver, kidney, and gill samples were obtained for biological and histological analysis. Goldfish in two treatments (1.0 mM and 10 mM) experienced irreversible oxidation of hemoglobin known as metahemoglobemia, marked by browning of the blood and darker tissues. Biochemical analysis showed an increase of nitrite in brain, nose, liver, and gill tissues. Brain and nose tissues (240 ±0.004 μM and 260 ±0.002 μM, respectively) accumulated more nitrite than gill tissue (190 ±0.002 μM) in the lowest treatment (0.3 mM), and this trend continued as treatment concentrations increased. Preliminary statistical analysis demonstrated that both the brain and nose tissue accumulated &gt;30% more nitrite than gill tissue in the 0.3 mM treatment. Histological analysis of the olfactory epithelium showed hyperplasia, an increase in cell size and number; furthermore, we observed an increase in the number of mucus cells and mucus production, collapse of columnar cells, and lamella constriction in both the 1.0 mM and 10 mM treatments. Histological analysis of gills showed lamella fusion and vascular congestion. Histological liver samples exhibited melanomacrophage aggregate, nucleus degeneration, and cytoplasmic vacuolation in 10 mM. Preliminary findings from electro‐olfactograms show that nitrite reduced the ability of a goldfish to detect odors at nitrite exposure as low as 0.1 mM. These results suggest that nitrite is accumulating faster in external sensory tissues than internal organs, affecting essential physiological processes such as olfactory food detection and possibly acting as a neurotoxin.Support or Funding InformationResearch support: Texas State University start‐up funding to Dr. Mar Huertas.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Продукционные характеристики морской диатомовой водоросли Cylindrotheca closterium (Ehrenb.) Reimann et Lewin в интенсивной культуре при различных источниках азота в питательной среде

Диатомовая водоросль Cylindrotheca closterium (Ehrenb.) Reimann et Lewin характеризуется высокой продуктивностью (до 1,5 гсух·л-1·сут-1) и способностью накапливать ценный каротиноид фукоксантин (до 2 % от сухой массы). Азот является одним из важнейших компонентов в питательной среде, существенно влияющих на продукционные характеристики микроводорослей. Цель работы — сравнить продукционные характеристики C. closterium при использовании разных форм азота в питательной среде в интенсивной накопительной культуре. В первом эксперименте источником азота служили нитрат и нитрит натрия, мочевина, азот в аммонийной форме. Отношение азота к фосфору (N : P) составляло 15 : 1. Во втором эксперименте источником азота служили аргинин, аспарагин и цистеин. Показана возможность использования диатомеей C. closterium для своего роста различных органических источников азота: мочевины, цистеина, аспарагина. Определены продукционные характеристики в интенсивной накопительной культуре C. сlosterium при применении мочевины, цистеина и аспарагина в качестве единственного источника азота в питательной среде RS. Показано, что при добавлении мочевины продуктивность достигала своих максимальных величин — 1,5 гсух·л-1·сут-1. Использование цистеина в стационарной фазе роста также целесообразно для увеличения времени этой фазы при минимальных концентрациях источника азота в питательной среде. Установлено, что C. сlosterium способна расти и вегетировать при достаточно высоких концентрациях нитрита; добавление азота в аммонийной форме в питательную среду во время активного роста водоросли приводит к ингибированию всех процессов метаболизма и к гибели культуры. При выращивании диатомеи для получения максимального выхода биомассы целесообразно применять мочевину в качестве дополнительного источника азота: именно при её добавлении зафиксированы максимальная продуктивность микроводоросли и продолжительная стационарная фаза роста, способствующая дальнейшему синтезу фукоксантина в культуре.

Evaluation of Oxidative Species in Gaseous and Liquid Phase Generated by Mini-Gliding Arc Discharge

The gliding arc discharge plasma reactors are known as a source of non-equilibrium plasma at atmospheric pressure. In the present study, generation of dominant reactive oxygen and nitrogen species in gaseous and liquid phase in water by the compact gliding arc device (mini-GAD) and corresponding bactericidal effects were investigated. Water and phosphate buffer solutions were used as model liquids. Mini-GAD is a strong source of nitrogen oxides (up to 800 ppm NO and 200 ppm NO2) that result in high concentrations of nitrites and nitrates in water solutions. The highest bactericidal efficacy towards Escherichia coli was achieved for non-buffered water solution.

Minimization of dissolved methane, nitrogen and organic micropollutants emissions of effluents from a methanogenic reactor by using a preanoxic MBR post-treatment system

The use of a hybrid membrane bioreactor (MBR) post-treatment system is proposed as a cost-efficient technology in order to minimize the environmental impact of anaerobic effluents, treating low-strength sewage at room temperature, such as their high nitrogen content and the presence of dissolved methane. In this research, nitrite was externally added at different concentrations into the anoxic compartment, providing an extra electron acceptor besides the existing nitrate, to evaluate its effect on denitrification, methane oxidation and OMPs removal processes. The nitrite addition significantly improved the denitrification potential of the system, achieving nitrogen removals up to 35 mg TN L−1. Moreover, higher nitrite concentrations clearly promoted an increase in the removal of some organic micropollutants (OMPs) such as diclofenac (DCF), ethinylestradiol (EE2), triclosan (TCS) and ibuprofen (IBP). Nevertheless, methane removal efficiencies or rates were not affected by this fact. Finally, COD and ammonium removals higher than 99 and 91% were observed during the entire operation, respectively. Based on the results, a future strategy in which ammonium is partially oxidized to nitrite could result in better nitrogen and OMPs removals for the proposed technology.

Survival of probiotic Lactobacillus plantarum and Enterococcus faecium in alginate beads during stress treatments

Purpose This study aims to protect Lactobacillus plantarum and Enterococcus faecium encapsulated in alginate beads during stress treatments, such as high temperatures and concentrations of sodium chloride (NaCl) and sodium nitrite (NaNO2). Design/methodology/approach Free and encapsulated probiotics were subjected to 70 and 80°C during 5, 10, 20 and 30 min. In addition, the probiotics were subjected to concentrations of 0.5, 1.0, 2.5 and 5.0 per cent NaCl and 0.5 and 1.0per cent of NaNO2. Findings Free Lactobacillus plantarum was more resistant to heat than free Enterococcus faecium. Alginate-encapsulated Lactobacillus plantarum (ALP) also was more resistant to heat treatments than alginate-encapsulated Enterococcus faecium (AEF). After 30 min at 70°C, ALP showed levels about 6.9 log CFU/g while AEF presented 4.3 log CFU/g (p = 0.005). However, at 80°C, ALP maintained levels higher than 6 log CFU/g for up to 10 min, while AEF was able to maintain those levels only for approximately 5 min (p = 0.003). Encapsulation process provided adequate protection for both probiotics against NaCl. In relation to NaNO2 concentrations, 0.5 and 1.0 per cent reduced viability of both probiotics (p = 0.014), either as free cells or as alginate-encapsulated forms. Practical implications Alginate beads containing probiotics is an interesting alternative for application in foods such as cooked meat products. Originality/value Alginate beads elaborated with milk powder, inulin and trehalose were effective to protect probiotics in stress situations similar to those can be found in the processing of foods, such as cooked meat products.

Intense rainfalls trigger nitrite leaching in agricultural soils depleted in organic matter

Nitrate and ammonium are common inorganic contaminants of anthropogenic origin in many shallow aquifers around the world, while nitrite is less common, but it is most harmful than nitrate and ammonium due to its high reactivity. This paper presents evidence of nitrite accumulation after intense rainfalls in soil samples collected in an agricultural field characterized by organic matter chronic depletion. Moreover, an intact core from the same site was also collected to perform an unsaturated column experiment (60 cm long and 20 cm outer diameter) mimicking heavy rainfalls (230 mm in 2 days). Results from the field site showed nitrite accumulation (up to 0.45 mmol/kg) at 50–70 cm depth, just below the plough layer. The column experiment showed very high initial concentrations of nitrate and nitrite in the leachate and a progressive decrease of nitrate due to denitrification. The numerical flow model was calibrated versus the observed volumetric water contents and leachate flow rates. The numerical reactive transport model was calibrated versus the leachate concentrations of six dissolved species (ammonium, nitrate, nitrite, dissolved organic carbon, chloride and bromide). The optimized model resulted to be robustly calibrated providing insights on the kinetic rates driving the production, accumulation and leakage of nitrite, showing that incomplete denitrification is the source of nitrite. As far as the authors are aware, this is the first study reporting a clear link between high nitrite leaching rates and extreme rainfall events in lowland agricultural soils depleted in organic matter. The proposed methodology could be applied to quantify nitrite cycling processes in many other agricultural areas of the world affected by extreme rainfall events.

Cationic Dye Modified Sawdust as Electrode Modifier for Electrochemical Detection of Anions

AbstractBecause of its chemical properties, sawdust displays poor anionic exchange capacity. Here we demonstrate that sawdust modification with methylene blue (MB) dye represents an interesting and facile alternative to render this natural biomaterial capable to accumulate anionic species. MB adsorption onto sawdust was monitored by cyclic voltammetry and experimental parameters carefully optimized. Under the ideal experimental conditions (composition of accumulation and desorption solution, accumulation and desorption time and the nature of the electrolytic solution), the adsorbed MB showed poor mobility, which results in the absence of the characteristic electrochemical signal of MB. The ability of the material to accumulate anionic species was thus evaluated using Fe(CN)63− as a model anions. The slow Fe(CN)63−/4− system recorded onto the electrode modified by pristine sawdust (P/SFE) become fast and reversible after immobilization of MB onto P/SFE (MB/SFE). Electrochemical impedance spectroscopy confirms this result through the spectacular decrease of charge transfer resistance after MB adsorption (from 83 kΩ on P/SFE to 637 Ω on MB/SFE). MB/SFE was applied to the electroanalysis of nitrites and a sensitivity of 7.4 μA mM−1 was obtained. Although this sensitivity was less important compared to that obtained on glassy carbon electrode (9.4 μA mM−1), the dye modified electrode displays by far the best reproducibility even at higher nitrite concentration.