Elevated Nitrite Concentrations Research Articles

Comparing methanol and glycerol as carbon sources for mainstream partial denitrification/anammox in an IFAS process.

This study explored the implementation of mainstream partial denitrification with anammox (PdNA) in the second anoxic zone of a wastewater treatment process in an integrated fixed film activated sludge (IFAS) configuration. A pilot study was conducted to compare the use of methanol and glycerol as external carbon sources for an IFAS PdNA startup, with a goal to optimize nitrogen removal while minimizing carbon usage. The study also investigated the establishment of anammox bacteria on virgin carriers in IFAS reactors without the use of seeding, and it is the first IFAS PdNA startup to use methanol as an external carbon source. The establishment of anammox bacteria was confirmed in both reactors 102 days after startup. Although the glycerol-fed reactor achieved a higher steady-state maximum ammonia removal rate because of anammox bacteria (1.6 ±0.3g/m2/day) in comparison with the methanol-fed reactor (1.2±0.2g/m2/day), both the glycerol- and methanol-fed reactors achieved similar average in situ ammonia removal rates of 0.39 ±0.2g/m2/day and 0.40 ±0.2g/m2/day, respectively. Additionally, when the upstream ammonia versus NOx (AvN) control system maintained an ideal ratio of 0.40-0.50 g/g, the methanol-fed reactor attained a lower average effluent TIN concentration (3.50 ±1.2mg/L) than the glycerol-fed reactor (4.43 ±1.6mg/L), which was prone to elevated nitrite concentrations in the effluent. Overall, this research highlights the potential for PdNA in IFAS configurations as an efficient and cost-saving method for wastewater treatment, with methanol as a viable carbon source for the establishment of anammox bacteria. PRACTITIONER POINTS: Methanol is an effective external carbon source for an anammox startup that avoids the need for costly alternative carbon sources. The methanol-fed reactor demonstrated higher TIN removal compared with the glycerol-fed reactor because of less overproduction of nitrite. Anammox bacteria was established in an IFAS reactor without seeding and used internally stored carbon to reduce external carbon addition. Controlling the influent ammonia versus NOx (AvN) ratio between 0.40 and 0.50 g/g allowed for low and stable TIN effluent conditions.

Extracorporeal cardio-pulmonary resuscitation in a patient with missed diagnosis of sodium nitrite intoxication.

Critical poisoning with sodium nitrite (NaNO2) can present challenges in promptly identifying and managing acute methemoglobinemia. We report the case of an overt self-intoxication by an initially unknown agent, leading to cardiac arrest. Despite prodromal signs of cyanosis, coma, desaturation, and hypotension, methemoglobinemia went unrecognized during extracorporeal cardiopulmonary resuscitation (ECPR) as the point-of-care test failed to provide methemoglobin levels, leading to untreated methemoglobinemia. The blood flowing through the oxygenator notably maintained the same brown colour. Return of spontaneous circulation was never achieved, and the patient was declared dead after 60min of unsuccessful resuscitation. Cause of death by means of NaNO2 voluntary ingestion was later clarified and confirmed by postmortem finding of elevated nitrite and nitrate concentration. This case highlights the risk of failure of ECPR in the context of cardiac arrest due to methemoglobinemia, emphasizing the critical need for prompt recognition of the causative agent and early administration of antidotes.

Impact of anthropogenic accumulation on phytoplankton community and harmful algal bloom in temporarily open/closed estuary

Spatio-temporal variation in phytoplankton community dynamics in a temporarily open/closed Swarnamukhi river estuary (SRE), located on the South East coast of India was investigated and correlated to that of the adjacent coastal waters. Understanding the seasonal variability of the phytoplankton community and influencing factors are essential to predicting their impact on fisheries as the river and coastal region serve as the main source of income for the local fishing communities. Downstream before the river meets the sea, an arm of the Buckingham Canal (BC), carrying anthropogenic inputs empties into the Swarnamukhi River (SR1). The impact of anthropogenic effects on the phytoplankton community at BC was compared to other estuarine stations SR2 (upstream), SR1 (downstream), SRM (river mouth) and coastal station (CS). In BC station, harmful algal blooms (HABs) of Chaetoceros decipiens (2940 × 103 cells L−1) and Oscillatoria sp. (1619 × 103 cells L−1) were found during the southwest monsoon and winter monsoon, respectively. These HABs can be linked to the anthropogenic input of increased nutrients and trace metals. The HABs of Oscillatoria sp. were shown to be induced by elevated concentrations of nitrate (10.18 µM) and Ni (3.0 ppm) compared to ambient, while the HABs of C. decipiens were caused by elevated concentrations of silicate (50.35 µM), nitrite (2.1 µM), and phosphate (4.37 µM). Elevated nutrients and metal concentration from the aquaculture farms, and other anthropogenic inputs could be one of the prime reasons for the recorded bloom events at BC station. During this period, observed bloom species density was found low at other estuarine stations and absent at CS. The formation of bloom events during the closure of the river mouth could be a major threat to the coastal ecosystem when it opens. During the Osillatoria sp. bloom, both the Cu and Ni levels were higher at BC. The elevated concentration of nutrients and metals could potentially affect the coastal ecosystem and in turn fisheries sector in the tropical coastal ecosystem.

Unraveling the molecular mechanisms of nitrite-induced physiological disruptions in largemouth bass

Largemouth bass (LMB; Micropterus salmoides) is an economically consequential piscine species spanning North America, Europe, and China. Elevated nitrite concentrations in aquatic environments cause significant physiological changes in fish, including stunted growth, appetite changes, reduced feed intake, and impaired oxygen transport, collectively affecting overall fish health. This study embarked on uncovering the molecular mechanisms underscoring the influence of various nitrite concentrations (0 mg/L, 400 mg/L, 600 mg/L, and 600 mg/L followed by recovery in nitrite-free water) on LMB, leveraging transcriptomics and metabolomics. Our findings revealed that a nitrite exposure of 400/600 mg/L may incite temporary, recoverable damage to the spleen, heart, and gills, but potentially enduring, irreversible hepatic pathologies. The spleen emerged as the most vulnerable organ to nitrite-induced deleterious impacts, causing acute, reversible damage and widespread apoptosis. Nitrite reprogramed splenocyte gene expressions, and prompted apoptosis, autophagy, and changes in metabolic pathways. It also triggered cell-type transitions and promoted adhesion-related gene expressions, as well as inhibited nucleotide metabolism and cell cycle progression. Notably, the immune cell repertoire within the spleen was affected by different nitrite concentrations, possibly linking to nitrite-induced spleen tissue impairment. Following the construction of a LMB protein–protein interaction (PPI) network, several pivotal genes uniquely expressed in distinct nitrite concentrations were identified, such as hdac4, hdac5, and brg1 in the N2 group (400 mg/L), hdac1, hells, and nccrp1 in the N3 group (600 mg/L), and Actr1, brd4, atf7a, and kat2b in the N4 group (600 mg/L recovery). The LMB spleen transcriptome was most profoundly influenced in the N3 group. Applying the MCODE algorithm for network module segmentation, we discerned eight MCODE subnetworks. Detailed analyses of these subnetworks shed light on their core functional pathways and pivotal genes. In particular, the MCODE1 core network implicated mainly Notch-HLH transcription, histone deacetylation, and protein deacetylation pathways, with pivotal genes such as ESRRGB, ATF7A, JDP2A, BRD4, and THRB. Metabolomic analysis results paralleled those of transcriptomic examination, corroborating analogous metabolic pathway alterations. This study holds substantial implications for comprehending the toxicological impact of nitrite on economically important fish species like LMB, and provides insights for refining aquaculture practices to minimize this toxicity.

Decoupling the simultaneous effects of NO2−, pH and free nitrous acid on N2O and NO production from enriched nitrifying activated sludge

In the pursuit of energy and carbon neutrality, nitrogen removal technologies have been developed featuring nitrite (NO2−) accumulation. However, high NO2− accumulations are often associated with stimulated greenhouse gas (i.e., nitrous oxide, N2O) emissions. Furthermore, the coexistence of free nitrous acid (FNA) formed by NO2− and proton (pH) makes the consequence of NO2− accumulation on N2O emissions complicated. The concurrent three factors, NO2−, pH and FNA may play different roles on N2O and nitric oxide (NO) emissions simultaneously, which has not been systematically studied. This study aims to decouple the effects of NO2− (0-200 mg N/L), pH (6.5-8) and FNA (0-0.15 mg N/L) on the N2O and NO production rates and the production pathways by ammonia oxidizing bacteria (AOB), with the use of a series of precisely executed batch tests and isotope site-preference analysis. Results suggested the dominant factors affecting the N2O production rate were NO2− and FNA concentrations, while pH alone played a relatively insignificant role. The most influential factor shifted from NO2− to FNA as FNA concentrations increased from 0 to 0.15 mg N/L. At concentrations below 0.0045 mg HNO2-N/L, nitrite rather than FNA played a significant role stimulating N2O production at elevated nitrite concentrations. The inhibition effect of FNA emerged with further increase of FNA between 0.0045-0.015 mg HNO2-N/L, weakening the promoting effect of increased nitrite. While at concentrations above 0.015 mg HNO2-N/L, FNA inhibited N2O production especially from nitrifier denitrification pathway with the level of inhibition linearly correlated with the FNA concentration. pH and the nitrite concentration regulated the production pathways, with elevated pH promoting the nitrifier nitrification pathway, while elevated NO2− concentrations promoting the nitrifier denitrification pathway. In contrast to N2O, NO emission was less susceptible to FNA at concentrations up to 0.015 mg N/L but was stimulated by increasing NO2− concentrations. This study, for the first time, distinguished the effects of pH, NO2− and FNA on N2O and NO production, thereby providing support to the design and operation of novel nitrogen removal systems with NO2− accumulation.

Activity of Ammonium-Oxidizing Bacteria—An Essential Parameter for Model-Based N2O Mitigation Control Strategies for Biofilms

The reduction in N2O emissions is an important task in the control of wastewater treatment plants. Since local operating conditions, especially inside biofilms, are usually not known, models are an important tool in the development and implementation of control strategies. For a pilot-scale nitrifying biofilm reactor and an SBR, different operational strategies to reduce autotrophic nitrous oxide (N2O) formation were developed and tested by applying a combination of modeling and measurement. Both approaches highlighted the relevance of addressing the actual AOB activity as a sensitive control variable. The investigated strategies, therefore, focused on decreasing the AOB-related NH4 conversion rate, as autotrophic N2O formation is directly linked to AOB activity. The results showed that the biofilm system was more advantageous compared with suspended sludge systems. A higher AOB content resulted in a decrease in AOB activity, leading to fewer N2O emissions at the same reactor performance. The highest reduction in autotrophic N2O formation (SBR: 25%; Biofilm: 27%) was obtained by maximizing the aerated time per day and minimizing the number of aeration cycles (the suppression of nitrite-oxidizing bacteria still needed to be ensured). A higher biofilm thickness or a higher sludge mass in the SBR, however, did not have a noteworthy positive effect since no additional biomass could be kept in the system in the long term due to limited substrate availability. Besides nitritation, denitrification was also identified as a relevant source of N2O in both systems (biofilm: main source) due to the inhibition of N2O reduction by nitrous acid (elevated nitrite concentrations in combination with pH values < 7).

Double-edged sword effects of dissimilatory nitrate reduction to ammonium (DNRA) bacteria on anammox bacteria performance in an MBR reactor

Dissimilatory nitrate reduction to ammonium (DNRA) bacteria imposing double-edged sword effects on anammox bacteria were investigated in an anammox-membrane bioreactor (MBR) experiencing an induced crash-recovery event. During the experiment, the anammox-MBR was loaded with NH4+-N:NO2−-N ratios (RatioNH4+-N: NO2−-N) of 1.20–1.60. Initially, the anammox-MBR removed over 95% of 100 mg/L NH4+-N and 132 mg/L NO2−-N (RatioNH4+-N: NO2−-N = 0.76, the well accepted stoichiometric RatioNH4+-N: NO2−-N for anammox) in the influent (Stage 0). Then, we induced a system crash-recovery event via nitrite shock loadings to better understand responses from different guilds of bacteria in anammox-MBR, loaded with 1.60 RatioNH4+-N: NO2−-N with 100 mg/L NO2−-N in the influent (Stage 1). Interestingly, the nitrogen removal by anammox bacteria was maintained for about 20 days before starting to decrease significantly. In Stage 2, we further increased influent nitrite concentration to 120 mg/L (1.33 RatioNH4+-N: NO2−-N) to simulate a high nitrite toxicity scenario for a short period of time. As expected, nitrogen removal efficiency dropped to only 16.8%. After the induced system crash, anammox-MBR performance recovered steadily to 93.2% nitrogen removal with a 1.25 RatioNH4+-N:NO2−-N and a low nitrite influent concentration of 80 mg/L NO2−-N. Metagenomics analysis revealed that a probable causality of the decreasing nitrogen removal efficiency in Stage 1 was the overgrowth of DNRA-capable bacteria. The results showed that the members within the Ignavibacteriales order (21.7%) out competed anammox bacteria (17.0%) in the anammox-MBR with elevated nitrite concentrations in the effluent. High NO2−-N loading (120 mg N/L) further caused the predominant Candidatus Kuenenia spp. were replaced by Candidatus Brocadia spp. Therefore, it was evident that DNRA bacteria posed negative effects on anammox with 1.60 RatioNH4+-N: NO2−-N. Also, when 120 mg/L NO2−-N fed to anammox-MBR (RatioNH4+-N: NO2−-N = 1.33), canonical denitrification became the primary nitrogen sink with both DNRA and anammox activities decreased. They probably fed on lysed microbial cells of anammox and DNRA. In Stage 3, a low RatioNH4+-N: NO2−-N (1.25) with 80 mg/L NO2−-N was used to rescue the system, which effectively promoted DNRA-capable bacteria growth. Although anammox bacteria's abundance was only 7.7% during this stage, they could be responsible for about 90% of the total nitrogen removal during this stage.

Impact of Sublethal Concentrations of Nitrite on Goldfish (Carassius auratus) Microbiomes.

Elevated concentrations of nitrite are toxic to fish and can cause a myriad of well documented issues. However, the effects of sublethal concentrations of nitrite on fish health, and specifically, fish tissue microbiomes have not been studied. To test the effects of nitrite exposure, goldfish were exposed to sublethal concentrations of nitrite, 0.0mM, 0.1mM, and 1.0mM, for 2months. The bacteria in the nose, skin, gills, and water were then extracted and sequenced to identify changes to the microbial composition. The water microbiome was not significantly changed by the added nitrite; however, each of the tissue microbiomes was changed by at least one of the treatments. The skin and gill microbiomes were significantly different between the control and 1.0mM treatment and the nose microbiome showed significant changes between the control and both the 0.1mM and 1.0mM treatments. Thus, sublethal concentrations of nitrite in the environment caused a shift in the fish tissue microbiomes independently of the water microbiome. These changes could lead to an increased chance of infection, disrupt organ systems, and raise the mortality rate of fish. In systems with high nitrite concentrations, like intensive aquaculture setups or polluted areas, the effects of nitrite on the microbiomes could negatively affect fish populations.

A nitrite-oxidising bacterium constitutively consumes atmospheric hydrogen

Chemolithoautotrophic nitrite-oxidising bacteria (NOB) of the genus Nitrospira contribute to nitrification in diverse natural environments and engineered systems. Nitrospira are thought to be well-adapted to substrate limitation owing to their high affinity for nitrite and capacity to use alternative energy sources. Here, we demonstrate that the canonical nitrite oxidiser Nitrospira moscoviensis oxidises hydrogen (H2) below atmospheric levels using a high-affinity group 2a nickel-iron hydrogenase [Km(app) = 32 nM]. Atmospheric H2 oxidation occurred under both nitrite-replete and nitrite-deplete conditions, suggesting low-potential electrons derived from H2 oxidation promote nitrite-dependent growth and enable survival during nitrite limitation. Proteomic analyses confirmed the hydrogenase was abundant under both conditions and indicated extensive metabolic changes occur to reduce energy expenditure and growth under nitrite-deplete conditions. Thermodynamic modelling revealed that H2 oxidation theoretically generates higher power yield than nitrite oxidation at low substrate concentrations and significantly contributes to growth at elevated nitrite concentrations. Collectively, this study suggests atmospheric H2 oxidation enhances the growth and survival of NOB amid variability of nitrite supply, extends the phenomenon of atmospheric H2 oxidation to an eighth phylum (Nitrospirota), and reveals unexpected new links between the global hydrogen and nitrogen cycles. Long classified as obligate nitrite oxidisers, our findings suggest H2 may primarily support growth and survival of certain NOB in natural environments.

Specific Denitrifying and Dissimilatory Nitrate Reduction to Ammonium Bacteria Assisted the Recovery of Anammox Community From Nitrite Inhibition.

The anaerobic ammonium oxidation (anammox) by autotrophic anaerobic ammonia-oxidizing bacteria (AnAOB) is a biological process used to remove reactive nitrogen from wastewater. It has been repeatedly reported that elevated nitrite concentrations can severely inhibit the growth of AnAOB, which renders the anammox process challenging for industrial-scale applications. Both denitrifying (DN) and dissimilatory nitrate reduction to ammonium (DNRA) bacteria can potentially consume excess nitrite in an anammox system to prevent its inhibitory effect on AnAOB. However, metabolic interactions among DN, DNRA, and AnAOB bacteria under elevated nitrite conditions remain to be elucidated at metabolic resolutions. In this study, a laboratory-scale anammox bioreactor was used to conduct an investigation of the microbial shift and functional interactions of AnAOB, DN, and DNRA bacteria during a long-term nitrite inhibition to eventual self-recovery episode. The relative abundance of AnAOB first decreased due to high nitrite concentration, which lowered the system’s nitrogen removal efficiency, but then recovered automatically without any external interference. Based on the relative abundance variations of genomes in the inhibition, adaptation, and recovery periods, we found that DN and DNRA bacteria could be divided into three niche groups: type I (types Ia and Ib) that includes mainly DN bacteria and type II and type III that include primarily DNRA bacteria. Type Ia and type II bacteria outcompeted other bacteria in the inhibition and adaptation periods, respectively. They were recognized as potential nitrite scavengers at high nitrite concentrations, contributing to stabilizing the nitrite concentration and the eventual recovery of the anammox system. These findings shed light on the potential engineering solutions to maintain a robust and efficient industrial-scale anammox process.

Toxicokinetic of Sublethal Concentrations of Nitrite in Goldfish (Carassius auratus)

Increased agriculture and industrial activity have elevated the concentration of nitrogenous compounds in the terrestrial and aquatic ecosystems. Nitrogenous compounds can naturally occur in aquatic ecosystems, concentrations are controlled and maintained through the nitrogen cycle by bacterial denitrification/nitrification. As large quantities of nitrogenous compounds drain into streams and rivers it can dramatically alter the natural nitrogenous concentrations in aquatic ecosystems. Nitrite is an intermediate compound in the nitrogen cycle, and its concentrations can range from 1 mM to 0.5 mM in freshwater and marine ecosystems. Exposure to elevated nitrite concentrations can disrupt physiological and endocrine processes such as ion and hormone regulation, respiratory, and cardiovascular activity. However, there is a lack of research in the effects of nitrite on sensitive organs such as the olfactory epithelium. Fish olfactory systems is highly sensitive and can detect odors in the picomolar concentration. To detect odors, this specialized sensitive system must be continuously exposed to the environment, making it highly susceptible to environmental toxins. We hypothesize olfactory tissues will be more sensitive to long term exposure to sub lethal concentrations of nitrite. Thus, the goal of this study is to determine the chronic effects of nitrite and its accumulation in the olfactory system and vital organs in goldfish (Carassius auratus). To test our hypothesis, goldfish were exposed to nitrite concentrations (0 mM, 10.0 μM, 100.0 μM, and 1000.0 μM) for 69 days. The nose, brain, gill, liver, kidney, and blood samples were collected on the last day of exposure. Samples were flash frozen (20°C) for biochemical analysis and subsamples were fixed in Bouin or 4% Paraformaldehyde (PFA). After 18hr, subsamples were transferred to ethanol or sucrose, respectively. Sub‐samples of flash frozen brains were dissected, hypothalamus samples were collected for RNA analysis. Notable browning or darkening of blood was seen in goldfish from 100.0 μM, and 1000.0 μM treatments, indicating irreversible oxidation of hemoglobin known as methemoglobinemia. Biochemical analysis showed nitrite accumulated in the nose, brain, and gill tissues (1.0 μM ±0.3, 8.1 μM ±1.4, and 11.1 μM ±0.4, respectively) in 100.0 μM treatment. Nitrite concentrations in these tissues increased as treatment concentration increased. RNA samples were prepared for qPCR analysis to measure gene expression related to appetite. Preliminary histological analysis of nose, gill, liver, and kidney tissues shows structural changes in tissues. The biochemical results indicate environmental concentrations of nitrite accumulate in vital tissues. Furthermore, findings indicate nitrite is entering and accumulating in the brain. These results suggest, nitrite is potentially acting as a neurotoxin.Support or Funding InformationResearch support: Texas State University start‐up funding to Dr. Mar Huertas.

Impact and tissue metabolism of nitrite at two acclimation temperatures in striped catfish (Pangasianodon hypophthalmus)

Elevated concentrations of nitrite develop occasionally in various aquatic habitats and aquaculture facilities, providing a potential danger for freshwater fish that take up nitrite via the gill chloride uptake mechanism. We studied the uptake, effects and metabolism of nitrite in blood, heart and skeletal muscle at two temperatures in striped catfish Pangasianodon hypophthalmus, a facultative air-breathing fish that is heavily cultivated in Southeast Asia. Exposure to 0.8 mM ambient nitrite increased blood [nitrite] and [methaemoglobin] (metHb) to high values at day 1, but values subsequently decreased towards controls at day 7. Blood [nitrite] and metHb content were unexpectedly higher at 27 °C (∼1.2 mM; 69% at day 1) than at 33 °C (∼0.9 mM; 55%), reflecting a lower nitrite uptake at the highest temperature, possibly via an increased reliance on air-breathing relative to water-breathing with temperature increase. A large fraction of the nitrite taken up was effectively eliminated by being detoxified to nitrate. Further, erythrocyte metHb reductase activity was increased during nitrite exposure, efficiently reducing metHb to functional haemoglobin. The uptake of nitrite into white skeletal musculature (main part of the fish) was much lower than into heart tissue. While heart [nitrite] was close to blood plasma levels, muscle [nitrite] peaked at ∼0.2 mM at day 1 and subsequently declined to ∼0.05 mM at day 7, which is below levels reported in various commercial cured meat products. Nitrite was partly metabolized to iron-nitrosyl, S-nitroso and N-nitroso compounds. The increase in nitros(yl)ated compounds was marginal in skeletal muscle and more pronounced in heart tissue.

First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System

AbstractThe northeastern Atlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. Anoxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen consumption for many months. Based on circumstantial in situ observations, this study demonstrates that the Senegalese coastal ocean is subjected to episodic occurrence of zero dissolved oxygen concentration at depth along with elevated nitrite concentration (11 mmol/m3) and nitrate/nitrite deficit to phosphate, thereby indicating severe anoxia and intense nitrogen loss. The anoxic event was associated with a prolonged upwelling relaxation episode in March 2012 and a nearshore diatom bloom that underwent degradation while being advected offshore in stratified waters. This is consistent with scenarios observed in other upwelling systems (Benguela and California), and such conditions are presumably frequent in the southern part of the Canary system.

Benthic nitrite exchanges in the Seine River (France): An early diagenetic modeling analysis

Nitrite is a toxic intermediate compound in the nitrogen (N) cycle. Elevated concentrations of nitrite have been observed in the Seine River, raising questions about its sources and fate. Here, we assess the role of bottom sediments as potential sources or sinks of nitrite along the river continuum. Sediment cores were collected from two depocenters, one located upstream, the other downstream, from the largest wastewater treatment plant (WWTP) servicing the conurbation of Paris. Pore water profiles of oxygen, nitrate, nitrite and ammonium were measured. Ammonium, nitrate and nitrite fluxes across the sediment-water interface (SWI) were determined in separate core incubation experiments. The data were interpreted with a one-dimensional, multi-component reactive transport model, which accounts for the production and consumption of nitrite through nitrification, denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA). In all core incubation experiments, nitrate uptake by the sediments was observed, indicative of high rates of denitrification. In contrast, for both sampling locations, the sediments in cores collected in August 2012 acted as sinks for nitrite, but those collected in October 2013 released nitrite to the overlying water. The model results suggest that the first step of nitrification generated most pore water nitrite at the two locations. While nitrification was also the main pathway consuming nitrite in the sediments upstream of the WWTP, anammox dominated nitrite removal at the downstream site. Sensitivity analyses indicated that the magnitude and direction of the benthic nitrite fluxes most strongly depend on bottom water oxygenation and the deposition flux of labile organic matter.

Survival, reproduction, growth, and parasite resistance of aquatic organisms exposed on-site to wastewater treated by advanced treatment processes

Advanced wastewater treatment technologies are generally known to be an effective tool for reducing micropollutant discharge into the aquatic environment. Nevertheless, some processes such as ozonation result in stable transformation products with often unknown toxicity. In the present study, whole effluents originating from nine different steps of advanced treatment combinations were compared for their aquatic toxicity. Assessed endpoints were survival, growth and reproduction of Lumbriculus variegatus, Daphnia magna and Lemna minor chronically exposed in on-site flow-through tests based on standard guidelines. The treatment combinations were activated sludge treatment followed by ozonation with subsequent filtration by granular activated carbon or biofilters and membrane bioreactor treatment of raw wastewater followed by ozonation. Additionally, the impact of treated wastewater on the immune response of invertebrates was investigated by challenging D. magna with a bacterial endoparasite. Conventionally treated wastewater reduced reproduction of L. variegatus by up to 46%, but did not affect D. magna and L. minor with regard to survival, growth, reproduction and parasite resistance. Instead, parasite susceptibility was significantly reduced in D. magna exposed to conventionally treated as well as ozonated wastewater in comparison to D. magna exposed to the medium control. None of the three test organisms provided clear evidence that wastewater ozonation leads to increased aquatic toxicity. Rather than to the presence of toxic transformation products, the affected performance of L. variegatus could be linked to elevated concentrations of ammonium and nitrite that likely resulted from treatment failures.

Simulated mussel mortality thresholds as a function of mussel biomass and nutrient loading.

A freshwater “mussel mortality threshold” was explored as a function of porewater ammonium (NH4+) concentration, mussel biomass, and total nitrogen (N) utilizing a numerical model calibrated with data from mesocosms with and without mussels. A mortality threshold of 2 mg-N L−1 porewater NH4+ was selected based on a study that estimated 100% mortality of juvenile Lampsilis mussels exposed to 1.9 mg-N L−1 NH4+ in equilibrium with 0.18 mg-N L−1 NH3. At the highest simulated mussel biomass (560 g m−2) and the lowest simulated influent water “food” concentration (0.1 mg-N L−1), the porewater NH4+ concentration after a 2,160 h timespan without mussels was 0.5 mg-N L−1 compared to 2.25 mg-N L−1 with mussels. Continuing these simulations while varying mussel biomass and N content yielded a mortality threshold contour that was essentially linear which contradicted the non-linear and non-monotonic relationship suggested by Strayer (2014). Our model suggests that mussels spatially focus nutrients from the overlying water to the sediments as evidenced by elevated porewater NH4+ in mesocosms with mussels. However, our previous work and the model utilized here show elevated concentrations of nitrite and nitrate in overlying waters as an indirect consequence of mussel activity. Even when the simulated overlying water food availability was quite low, the mortality threshold was reached at a mussel biomass of about 480 g m−2. At a food concentration of 10 mg-N L−1, the mortality threshold was reached at a biomass of about 250 g m−2. Our model suggests the mortality threshold for juvenile Lampsilis species could be exceeded at low mussel biomass if exposed for even a short time to the highly elevated total N loadings endemic to the agricultural Midwest.

Short-term treatment with nitrate is not sufficient to induce in vivo antithrombotic effects in rats and mice

In humans, short-term supplementation with nitrate is hypotensive and inhibits platelet aggregation via an nitric oxide (NO)-dependent mechanism. In the present work, we analyzed whether short-term treatment with nitrate induces antithrombotic effects in rats and mice. Arterial thrombosis was evoked electrically in a rat model in which renovascular hypertension was induced by partial ligation of the left renal artery. In mice expressing green fluorescent protein, laser-induced thrombosis was analyzed intravitally by using confocal microscope. Sodium nitrate (NaNO3) or sodium nitrite (NaNO2) was administered orally at a dose of 0.17 mmol/kg, twice per day for 3 days. Short-term nitrate treatment did not modify thrombus formation in either rats or mice, while nitrite administration led to pronounced antithrombotic activity. In hypertensive rats, nitrite treatment resulted in a significant decrease in thrombus weight (0.50 ± 0.08 mg vs. VEH 0.96 ± 0.09 mg; p < 0.01). In addition, nitrite inhibited ex vivo platelet aggregation and thromboxane B2 (TxB2) generation and prolonged prothrombin time. These effects were accompanied by significant increases in blood NOHb concentration and plasma nitrite concentration. In contrast, nitrate did not affect ex vivo platelet aggregation or prothrombin time and led to only slightly elevated nitrite plasma concentration. In mice, nitrate was also ineffective, while nitrite led to decreased platelet accumulation in the area of laser-induced endothelial injury. In conclusion, although nitrite induced profound NO-dependent antithrombotic effects in vivo, conversion of nitrates to nitrite in rats and mice over short-term 3-day treatment was not sufficient to elicit NO-dependent antiplatelet or antithrombotic effects.

Platelet inhibitory effects of juices from Pachyrhizus erosus L. root and Psidium guajava L. fruit: a randomized controlled trial in healthy volunteers.

BackgroundThe purpose of this study is to investigate cardiovascular benefits of juices obtained from two commonly consumed fruits in Thailand, Pachyrhizus erosus, L. (yam bean) and Psidium guajava, L. (guava), by examining their acute cardiovascular effects in healthy volunteers. Possible involvements of the dietary nitrate on their effects were investigated as well.MethodThirty healthy volunteers were randomly divided into three groups of 10 subjects per group and each group was allocated to drink 500 ml of freshly prepared yam bean root juice, guava fruit juice, or water. Systemic nitrate and nitrite concentrations, heart rate, systolic and diastolic blood pressure, serum K+ concentrations, ex vivo platelet aggregation, and plasma cGMP concentrations were monitored at the baseline and at various time points after the intake of juices or water. Data were compared by repeated measures ANOVA.ResultsFollowing the ingestion of both yam bean root juice and guava fruit juice, collagen-induced but not ADP-induced platelet aggregation was attenuated. Ingestion of yam bean root juice increased systemic nitrate and nitrite concentrations whereby elevated nitrite concentrations correlated with the extent of inhibiting collagen-induced platelet aggregation. In addition, positive correlation between systemic nitrite and plasma cGMP concentrations and negative correlation between plasma cGMP concentrations and the extent of collagen-induced platelet aggregation were revealed. Nevertheless, yam bean root juice reduced only diastolic blood pressure while guava fruit juice reduced heart rate, systolic and diastolic blood pressure.ConclusionThe present study has illustrated, for the first time, acute inhibitory effects of yam bean root juice and guava fruit juice on ex vivo collagen-induced platelet aggregation in healthy subjects. Dietary nitrate was shown to underlie the effect of yam bean root juice but not that of guava fruit juice. Following yam bean root juice ingestion, systemic nitrate apparently converts to nitrite and further to NO which may attenuate platelet responses to collagen stimulation. Cardiovascular benefits of juices from yam bean root and guava fruit are noteworthy in term of the cardiovascular health-promoting approach.Trial registrationRandomized controlled trial TCTR20150228001.

NC10 bacteria in marine oxygen minimum zones.

Bacteria of the NC10 phylum link anaerobic methane oxidation to nitrite denitrification through a unique O2-producing intra-aerobic methanotrophy pathway. A niche for NC10 in the pelagic ocean has not been confirmed. We show that NC10 bacteria are present and transcriptionally active in oceanic oxygen minimum zones (OMZs) off northern Mexico and Costa Rica. NC10 16S rRNA genes were detected at all sites, peaking in abundance in the anoxic zone with elevated nitrite and methane concentrations. Phylogenetic analysis of particulate methane monooxygenase genes further confirmed the presence of NC10. rRNA and mRNA transcripts assignable to NC10 peaked within the OMZ and included genes of the putative nitrite-dependent intra-aerobic pathway, with high representation of transcripts containing the unique motif structure of the nitric oxide (NO) reductase of NC10 bacteria, hypothesized to participate in O2-producing NO dismutation. These findings confirm pelagic OMZs as a niche for NC10, suggesting a role for this group in OMZ nitrogen, methane and oxygen cycling.

Transcriptomic evidence for microbial sulfur cycling in the eastern tropical North Pacific oxygen minimum zone

Microbial communities play central roles in ocean biogeochemical cycles, and are particularly important in in oceanic oxygen minimum zones (OMZs). However, the key carbon, nitrogen, and sulfur (S) cycling processes catalyzed by OMZ microbial communities are poorly constrained spatially, temporally, and with regard to the different microbial groups involved. Here we sample across dissolved oxygen (DO) gradients in the oceans’ largest OMZ by volume—the eastern tropical North Pacific ocean, or ETNP—and quantify 16S rRNA and functional gene transcripts to detect and constrain the activity of different S-cycling groups. Based on gene expression profiles, putative dissimilatory sulfite reductase (dsrA) genes are actively expressed within the ETNP OMZ. dsrA expression was limited almost entirely to samples with elevated nitrite concentrations, consistent with previous observations in the Eastern Tropical South Pacific OMZ. dsrA and ‘reverse’ dissimilatory sulfite reductase (rdsrA) genes are related and the associated enzymes are known to operate in either direction—reducing or oxidizing different S compounds. We found that rdsrA genes and soxB genes were expressed in the same samples, suggestive of active S cycling in the ETNP OMZ. These data provide potential thresholds for S cycling in OMZs that closely mimic recent predictions, and indicate that S cycling may be broadly relevant in OMZs.