Peak NO3 Research Articles

Synergistic degradation efficiency of nitrogen, phosphorus and microbial dynamic succession driven by a novel strain Gordonia sp. D4 during synthetic wastewater treatment

Nitrogen (N) and phosphorus (P) coexist in the industrial and domestic wastewater posed a pressing challenge for synergistic removal of N and P by bioenhancement. In this study, a novel denitrifying phosphorus-accumulating organism (DPAO) of Gordonia sp. D4, exhibited peak NO3--N, NO2--N, NH4+-N and TP removal efficiencies of 98.11%, 65.02%, 85.34% and 100%, corresponding to 9.30 mg/(L·h), 6.08 mg/(L·h), 3.63 mg/(L·h) and 0.47 mg/(L·h) removal rates, respectively. Strain D4 contained the nitrogen cycling genes narK, narI, narJ, narH, narG, nirB and nirD, as well as the phosphorus cycling genes ppk1, ppk2 and ppx-gppA, which contributes to its excellent simultaneous removal of N and P. More importantly, the addition of D4 into the sequencing batch reactor (SBR) significantly improved the P, TN and NO3--N removal efficiencies by 18.91%, 7.35%, and 18.55%, respectively. This was closely related to the clear enrichment of Gordonia and its contribution to the increasing abundances of Pararhodobacter, unclassified_f_Cyclobacteriaceae, unclassified_o_Rhodospirillales, Thauera and Candidatus Promineofilum and their associated functional genes that drive P or N removal, thereby enhancing the N and P synergistic degradation efficiency. This study provides a valuable strain resource and process reference for the simultaneously removing N and P from the wastewater.

Sandy seepage faces as bioactive nitrate reactors: Biogeochemistry, microbial ecology and metagenomics

Subterranean estuaries are highly dynamic in processing dissolved inorganic nitrogen (DIN). Here we investigate DIN turnover in surface sediments (0–20 cm depth) at the higher, medium and lower intertidal of a seepage face, i.e., the outer “mouth” of the subterranean estuary, during four consecutive seasons in Sanggou Bay, China. Throughout the studied period, ammonium (NH4+) and nitrite (NO2−) concentrations in the sampled porewaters did not vary significantly with depth or season. In contrast, peaks in porewater nitrate (NO3−) concentration and decreases in δ15N-NO3− and δ18O-NO3− were observed in the 15–20 cm depth (bottom) sediment, particularly during summer and autumn. Coupled with NO3− production, the sediment total nitrogen was also markedly peaking in the bottom layer of the studied seepage face. Together with abundant heterotrophic microbes in the sediment, this NO3− accumulation was linked to a reaction chain including organic matter decomposition, ammonification and nitrification. During winter, porewater enrichment in total nitrogen occurred closer to the surface of the seepage face but triggered also active NO3− production. This pattern reinforced the importance of pelagic organic matter supply on NO3− production. In the shallower depths of the seepage face (<12 cm), active net NO3− removal occurred except in winter. The isotopic fractionation (δ15N-NO3− and δ18O-NO3−) and metagenomic results revealed denitrification as the main pathway for NO3− reduction. Biological assimilation from benthic primary producers may also consume a fraction of NO3− at the sediment water interface. Both NO3− production and removal significantly varied in magnitude with season (−13.6 to 6.2 nmol cm−3 h−1). Substrate supply was the key driver for nitrate cycling, as evidenced by the high NO3− production rate in spring by comparison to autumn. The highest NO3− turnover rates were found in summer, suggesting the combined influence of advection rates and sediment microbiota composition. In spite of active removal (peak NO3− removal capability: 61%), a significant amount of NO3− was still transported from the seepage face into the bay waters. The magnitude of NO3− fluxes ranged from 312 to 476 kg N d−1, accounting for approximately 15% of the total exogenous NO3− loading into the bay. NO3− isotopic fingerprint revealed chemical fertilizer as the main source of terrestrial NO3− in SGD, highlighting the importance of land use to coastal system nitrogen budgets.

High-frequency, in situ sampling of field woodchip bioreactors reveals sources of sampling error and hydraulic inefficiencies

Woodchip bioreactors are a practical, low-cost technology for reducing nitrate (NO3) loads discharged from agriculture. Traditional methods of quantifying their performance in the field mostly rely on low-frequency, time-based (weekly to monthly sampling interval) or flow-weighted sample collection at the inlet and outlet, creating uncertainty in their performance and design by providing incomplete information on flow and water chemistry. To address this uncertainty, two field bioreactors were monitored in the US and New Zealand using high-frequency, multipoint sampling for in situ monitoring of NO3–N concentrations. High-frequency monitoring (sub hourly interval) at the inlet and outlet of both bioreactors revealed significant variability in volumetric removal rates and percent reduction, with percent reduction varying by up to 25 percentage points within a single flow event. Time series of inlet and outlet NO3 showed significant lag in peak concentrations of 1–3 days due to high hydraulic residence time, where calculations from instantaneous measurements produced erroneous estimates of performance and misleading relationships between residence time and removal. Internal porewater sampling wells showed differences in NO3 concentration between shallow and deep zones, and “hot spot” zones where peak NO3 removal co-occurred with dissolved oxygen depletion and dissolved organic carbon production. Tracking NO3 movement through the profile showed preferential flow occurring with slower flow in deeper woodchips, and slower flow further from the most direct flowpath from inlet to outlet. High-frequency, in situ data on inlet and outlet time series and internal porewater solute profiles of this initial work highlight several key areas for future research.

Inland impacts of atmospheric river and tropical cyclone extremes on nitrate transport and stable isotope measurements

Atmospheric rivers and tropical cyclones originate in the tropics and can transport high rainfall amounts to inland temperate regions. The purpose of this study was to investigate the response of nitrate (NO3−) pathways, concentration peaks, and stable isotope (δ15NNO3, δ18ONO3, δ2HH2O, δ18OH2O, and δ13CDIC) measurements to these extreme events. A tropical cyclone and atmospheric river produced the number one and four ranked events in 2017, respectively, at a Kentucky USA watershed characterized by mature karst topography. Hydrologic responses from the two events were different due to rainfall characteristics with the tropical cyclone producing a steeper rising limb of the spring hydrograph and greater runoff generation to the surface stream compared to the atmospheric river. Local minima and maxima of specific conductance, δ2HH2O, δ18OH2O, and δ13CDIC coincided with hydrograph peaks for both events. Minima and maxima of NO3−, δ15NNO3, δ18ONO3, and temperature lagged behind the hydrograph peak for both events, and the values continued to be impacted by diffuse recharge during hydrograph recession. Quick-flow pathways accounted for less than 20% of the total NO3− yield, while intermediate (30%) and slow-flow (50%) pathways composed the remaining load. However, hydrograph separation into quick-, intermediate-, and slow-flow pathways was not able to predict the timing of NO3− concentration peaks. Rather, the intermediate-flow pathway is conceptualized to experience a shift in porosity, associated with a change from epikarst macropores and fissures to soil micropores, with the arrival of water from the latter component likely causing peak NO3− concentration at the spring. Our results suggest that a more discretized conceptual model of pathways may be needed to predict peak nutrient concentration in rivers draining karst topography.

High‐Frequency Sensor Data Reveal Across‐Scale Nitrate Dynamics in Response to Hydrology and Biogeochemistry in Intensively Managed Agricultural Basins

AbstractExcess nitrate in rivers draining intensively managed agricultural watersheds has caused coastal hypoxic zones, harmful algal blooms, and degraded drinking water. Hydrology and biogeochemical transformations influence nitrate concentrations by changing nitrate supply, removal, and transport. For the Midwest Unites States, where much of the land is used for corn and soybean production, a better understanding of the response of nitrate to hydrology and biogeochemistry is vital in the face of high nitrate concentrations coupled with projected increases of precipitation frequency and magnitude. In this study, we capitalized on the availability of spatially and temporally extensive sensor data in the region to evaluate how nitrate concentration (NO3−) interacts with discharge (Q) and water temperature (T) within eight watersheds in Iowa, United States, by evaluating land use characteristics and multiscale temporal behavior from 5‐year, high‐frequency, time series records. We show that power spectral density of Q, NO3−, and T, all exhibit power law behavior with slopes greater than 2, implying temporal self‐similarity for a range of scales. NO3− was strongly cross correlated with Q for all sites and correlation increased significantly with drainage area across sites. Peak NO3− increased significantly with crop coverage across watersheds. Temporal offsets in peak NO3− and peak Q, seen at all study sites, reduced the impact of extreme events. This study illustrates a relatively new approach to evaluating environmental sensor data and revealed characteristics of watersheds in which extreme discharge events have the greatest consequences.

Global modeling of the nitrate radical (NO3) for present and pre-industrial scenarios

Increasing the complexity of the chemistry scheme in the global chemistry transport model STOCHEM to STOCHEM-CRI (Utembe et al., 2010) leads to an increase in NOx as well as ozone resulting in higher NO3 production over forested regions and regions impacted by anthropogenic emission. Peak NO3 is located over the continents near NOx emission sources. NO3 is formed in the main by the reaction of NO2 with O3, and the significant losses of NO3 are due to the photolysis and the reactions with NO and VOCs. Isoprene is an important biogenic VOC, and the possibility of HOx recycling via isoprene chemistry and other mechanisms such as the reaction of RO2 with HO2 has been investigated previously (Archibald et al., 2010a). The importance of including HOx recycling processes on the global budget of NO3 for present and pre-industrial scenarios has been studied using STOCHEM-CRI, and the results are compared. The large increase (up to 60% for present and up to 80% for pre-industrial) in NO3 is driven by the reduced lifetime of emitted VOCs because of the increase in the HOx concentration. The maximum concentration changes (up to 15ppt) for NO3 from pre-industrial to present day are found at the surface between 30oN and 60oN because of the increase in NOx concentrations in the present day integrations.

The effect of animal trampling and DCD on ammonia oxidisers, nitrification, and nitrate leaching under simulated winter forage grazing conditions

Dairy winter forage grazing on free-draining soils is a common practice within the Canterbury region of New Zealand. The high stocking rates involved and the associated deposition of urine onto wet soils during winter create a high risk of nitrate (NO3 −) leaching from soil. The objective of this study was to determine the effect of animal trampling and the use of a nitrification inhibitor, dicyandiamide (DCD), on soil ammonia oxidisers, nitrification, and nitrate leaching under simulated winter forage grazing conditions. A lysimeter trial was carried out using a Balmoral stony silt loam under a kale forage crop. Nitrate leaching losses, the effect of soil trampling, and the effect of DCD were measured. Soil nitrification rates and ammonia-oxidising community abundance and activity were measured in companion soil blocks under simulated dairy winter forage grazing conditions. Animal trampling was found to reduce peak nitrate-N (NO3 --N) concentrations in drainage water from urine patch areas by 43 %. In addition, animal trampling reduced the total amount of NO3 −-N leached from urine patches by 34 %. However, animal trampling did not affect the growth or activity of the ammonia oxidisers. The use of DCD was found to be highly effective in reducing the concentration and amount of NO3 −-N leached from urine patches. Dicyandiamide applications reduced peak NO3 −-N concentrations in drainage water by 66 %, and the total amount of NO3 −-N leached was reduced by 61 % under the simulated dairy winter forage grazing conditions. Ammonia oxidising bacteria (AOB) were more abundant than ammonia-oxidising archaea (AOA) and were responsible for mediating the nitrification process. These results suggest that both animal trampling and the use of DCD separately reduces soil nitrification rates and thus NO3 − leaching.

Soil water and nitrogen interaction effect on residual soil nitrate and crop nitrogen recovery under maize–wheat cropping system in the semi-arid region of northern India

Over fertilization of nitrogen (N) in the premise of higher crop yield has sometimes led to build up of residual soil nitrate and pollution of ground water. Though, maize and wheat are two heavy feeders of N, studies on soil nitrate dynamics under maize–wheat cropping system in the Indo-Gangetic Plains of northern India, are limited. Hence, the present study was carried out at the research farm of Indian Agricultural Research Institute, New Delhi with maize–wheat cropping sequence grown for four consecutive cropping seasons, during 2002–2004. The treatments consisted of three levels of water regimes and five N levels taken in split plot design. Three levels of water regime, namely, W1, W2 and W3 referred to as limited, medium and maximum number of recommended irrigation. The five N levels were T1 (0% N), T2 (75% N), T3 (100% N), T4 (150% N) and T5 (100% N from organic source). For both the crops, 100% N corresponded to the recommended dose of 120kgNha−1 from inorganic source. Irrespective of crop, N recovery was higher under T2 and W3 treatment combination, though yield and biomass were highest under T4 and W3 treatments. Nitrogen recovery from organic treatment gradually increased from 8.8% in the first crop season (maize, 2002) to 26.1% in the last crop season of the experiment (wheat, 2004). Peak NO3− concentration was observed at 15–30cm soil depth in W1 and W2 treatments and at 30–60cm in W3 water regime. The NO3− buildup was higher in W1 as compared to W3 treatment and was to the extent of 62kgha−1 in the 0–120cm soil profile under W1T4 treatment after four crop seasons. Across water treatments, soil NO3− was higher under T4 (150% N), followed by T3 (100% N) throughout the experiment period. Despite a trend of soil NO3− buildup, application of N (150%) maximized crop productivity (maize and wheat) under W3. The study revealed that maize–wheat cropping system grown under higher N application levels beyond the recommended dose, would reduce N use efficiency and enhance soil nitrate buildup.

Night-time chemistry above London: measurements of NO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;5&amp;lt;/sub&amp;gt; from the BT Tower

Abstract. Broadband cavity enhanced absorption spectroscopy (BBCEAS) has been used to measure the sum of concentrations of NO3 and N2O5 from the BT (telecommunications) Tower 160 m above street level in central London during the REPARTEE II campaign in October and November 2007. Substantial variability was observed in these night-time nitrogen compounds: peak NO3+N2O5 mixing ratios reached 800 pptv, whereas the mean night-time NO3+N2O5 was approximately 30 pptv. Additionally, [NO3+N2O5] showed negative correlations with [NO] and [NO2] and a positive correlation with [O3]. Co-measurements of temperature and NO2 from the BT Tower were used to calculate the equilibrium partitioning between NO3 and N2O5 which was always found to strongly favour N2O5 (NO3/N2O5=0.01 to 0.04). Two methods are used to calculate the lifetimes for NO3 and N2O5, the results being compared and discussed in terms of the implications for the night-time oxidation of nitrogen oxides and the night-time sinks for NOy.

Interactive Effects of N Deposition, Land Management and Weather Patterns on Soil Solution Chemistry in a Scottish Alpine Heath

Nitrogen (N) deposition and land management practices can have profound impacts on the structure and functioning of alpine ecosystems occupying headwaters of major river systems. Such impacts have the potential to result in loss of N to surface waters and acidification, both of which could have serious consequences for water quality and downstream habitats. We present results from a 6-year study of Calluna-dominated alpine heathland in Scotland, designed to assess the interactive effects of N addition (0 and 50 kg N ha−1 y−l), simulated accidental fire and grazing on soil solution chemistry. Both N addition and to a lesser extent burning had significant effects on soil solution chemistry, whereas grazing had no significant impact. Soil solution nitrate (NO3 −) and ammonium (NH4 +) concentration showed a rapid response to N addition and N addition also resulted in acidification of soil solution. A ‘flush’ of base cations, which normally buffer soil from the acid effects of deposited N, accompanied the excess N released from the soil to soil solution. The N treatment had no effect on dissolved organic carbon (DOC), however, concentrations were significantly (14%) lower at the burned plots. In addition to treatment effects, temporal analysis of data from control plots demonstrated that soil solution chemistry was influenced by extremes in weather conditions. Peak NO3 − concentrations were observed in soil solution following the cold winter of 2000–2001 when there were frequent freeze/thaw events. A large pulse of base cations was lost from the soil following the dry year of 2003. These weather-induced responses potentially exacerbate the treatment effects observed in this study.

Response of Enteromorpha sp. (Chlorophyceae) to a nitrate pulse: nitrate uptake, inorganic nitrogen storage and nitrate reductase activity

The uptake, storage and reduction of nitrate (NO3 - ) by Enteromorpha sp. during a NO3 - pulse was studied in the laboratory using algae collected from the Mobile Bay estuary, Alabama, USA. Peak uptake occurred when Enteromorpha sp. was initially exposed to NO3 - . As the internal NO3 - pool filled, NO3 - uptake declined. After 6 h of exposure to a 30 µM NO3 - pulse, the tissue NO3 - pool was filled and NO3 - uptake decreased to 1.64 ± 2.63 µmol NO3 - g -1 fresh wt h -1 . While tissue NO3 - increased when NO3 - became available, the size of the internal nitrite (NO2 - ), ammonium (NH4 + ), and free amino acid (FAA) pools remained roughly constant, suggesting that reduction of NO3 - to nitrite (NO2 - ) by nitrate reductase (NR) was the rate-limiting step in NO3 - assimilation. Meanwhile, there was a lag time (2 to 3 h) between exposure to NO3 - and peak NR activity (0.80 ± 0.23 µmol NO2 - g -1 fresh wt h -1 ). These characteristics, combined with a peak NR activity that was 11-fold less than the peak NO3 - uptake rate, suggest that during a NO3 - pulse the internal NO3 - pool quickly fills and uptake becomes limited by the rate at which the internal NO3 - pool is reduced by NR. Predicted levels of tissue NO3 - calculated from initial tissue NO3 - , NO3 - uptake and NR activity agreed with the measured tissue NO3 - .

Prediction of Groundwater Nitrate Contamination after Closure of an Unlined Sheep Feedlot

Nitrate contamination of groundwater by a sheep feedlot in Hawke's Bay, New Zealand led to closure of the feedlot in 1998. However, knowledge of the processes controlling how long the contamination will remain and an analysis of whether the current land use (vineyard) will also impact groundwater quality are required to assess long‐term groundwater quality issues after feedlot operations cease. To determine the fate of NO3 following land use changes and the rate of reduction of contamination that may be expected under natural conditions following such changes, we compared the chemical concentrations of NO3–N, Cl, and alkalinity (HCO3) in the groundwater and rivers from surveys conducted in 1994 and 1995 with sampling conducted in 2001. Profile sampling of total N and C of the &lt;2‐mm size fraction in the vadose zone from two sites was used in a one‐dimensional soil–plant–atmosphere system model (SPASMO) program to predict N loading in future years and predict how long it would take to improve the groundwater quality. Groundwater sampling in 1994 and 1995 determined that the highest NO3–N concentrations were under the feedlot (&gt;140 g m−3 NO3–N) and down gradient. In 2001, 3 yr after the feedlot closed, the Cl concentrations had increased in down‐gradient wells but remained similar to the 1994 survey in other wells. There has been a decrease in NO3–N concentrations in most wells, compared with the peak NO3–N concentrations recorded in the 1995 survey, but an increase compared with 1994. Alkalinity concentrations in wells located within the influence of the feedlot are approximately 150 g m−3 lower than in surrounding wells. This indicates that nitrification reactions are affecting the HCO3 concentrations in the feedlot‐influenced wells. However, the HCO3 concentrations of some of these wells are increasing, indicating that nitrification could be slowing down and the aquifer is beginning to recover. SPASMO modeling indicates that NO3 contamination from the site will continue for the next 3 to 5 yr. The impact of NO3 leaching due to current land use practices is likely to be much less than the feedlot. The model predicts there will be an improvement in groundwater quality in the next 3 to 5 yr as NO3 from the feedlot eventually leaves the vadose zone profile and mixes into the unconfined aquifer.

Soil response to surface-applied residues of varying carbon-nitrogen ratios

A 5-year study was conducted to monitor patterns of NO3- accumulation following the addition of plant residues of varying C:N ratios to the soil surface, to determine whether the availability of NO3- following these applications would be timely and sufficient for typical annual crop uptake. Microbial respiration was measured in the last 3 years of the study to investigate how microbial activity was related to treatment differences in NO3- accumulation. Treatments included: hairy vetch (Vicia villosa Roth) cut at mid-bloom; wheat (Triticum aestivum L.) straw applied at 4 Mg ha-1; vetch with 4 Mg ha-1 wheat straw; and a bare ground control. Soil NO3- and respiration rates were correspondingly high for the 3–4 weeks following residue placement. Peak NO3--N accumulation in vetch treatments occurred between 25 June and 10 July and ranged from 100 to 168 kg ha-1, with an average of 140 kg NO3−-N ha-1. Nitrate was sufficient and timely enough to meet most summer annual crop needs in the region. Over 5 years, peak NO3−-N was approximately 100 kg ha-1 higher in vetch than non-vetch treatments and roughly twice as high at 0–5 cm than at 5–20 cm. The addition of wheat straw caused a reduction of approximately 20% NO3--N throughout the season as compared to vetch alone.

Tracking the fate of a high concentration groundwater nitrate plume through a fringing marsh: A combined groundwater tracer and in situ isotope enrichment study

A groundwater plume enriched in 15NO3− was created upgradient of a mesohaline salt marsh. By measuring the changes in concentration and isotopic enrichment of NO3−, N2O, N2, NH4+, and particulate organic nitrogen (PON) during plume transport through the marsh, in situ rates of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification (DNF) were estimated, as well as N storage in the reduced N pools. For groundwater discharge within the top 10 cm of marsh, NO3− removal was 90% complete within the 50 cm of marsh nearest the upland border. The peak NO3− loss rate from the plume ranged from 208 to 645 µM d−1. Rates of DNRA (180 µM d−1) and DNF (387–465 µM d−1) processed 30% and 70% of the NO3− load, respectively. Terminal N2 production was approximately equal to N2 production rates during DNF. Comparison of 15N lost from the 15NO3− pool and 15N gained in each of the reduced products accounted for only 22% of the reduced 15N, thus indicating N export from the system. Despite high rates of DNRA, the NH4+ produced was not a long‐term repository for the groundwater‐derived N but was instead rapidly immobilized into marsh PON and retained on longer timescales. The small inventory of 15N in the N2 and N2 pools relative to DNF rates, coincident with an undersaturation of dissolved argon, indicated that denitrified N was exported to the atmosphere on short timescales. The relative magnitudes of DNF and DNRA in conjunction with the immobilization of NH4+ and evasion of N gases dictated the extent of export versus retention of the groundwater NO3− load.

Exploring functional similarity in the export of Nitrate‐N from forested catchments: A mechanistic modeling approach

Functional similarity of catchments implies that we are able to identify the combination of processes that creates a similar response of a specific characteristic of a catchment. We applied the concept of functional similarity to the export of NO3−‐N from catchments situated within the Turkey Lakes Watershed, a temperate forest in central Ontario, Canada. Despite the homogeneous nature of the forest, these catchments exhibit substantial variability in the concentrations of NO3−‐N in discharge waters, over both time and space. We hypothesized that functional similarity in the export of NO3−‐N can be expressed as a function of topographic complexity as topography regulates both the formation and flushing of NO3−‐N within the catchment. We tested this hypothesis by exploring whether topographically based similarity indices of the formation and flushing of NO3−‐N capture the observed export of NO3−‐N over a set of topographically diverse catchments. For catchments with no elevated base concentrations of NO3−‐N the similarity indices explained up to 58% of the variance in the export of NO3−‐N. For catchments with elevated base concentrations of NO3−‐N, prediction of the export of NO3−‐N may have been complicated by the fact that hydrology was governed by a two‐component till, with an ablation till overlying a basal till. While the similarity indices captured peak NO3−‐N concentrations exported from shallow flow paths emanating from the ablation till, they did not capture base NO3−‐N concentrations exported from deep flow paths emanating from the basal till, emphasizing the importance of including shallow and deep flow paths in future similarity indices. The strength of the similarity indices is their potential ability to enable us to discriminate catchments that have visually similar surface characteristics but show distinct NO3−‐N export responses and, conversely, to group catchments that have visually dissimilar surface characteristics but are functionally similar. Furthermore, the similarity indices provide a potentially powerful method to scale and generalize NO3−‐N export responses to other regions.

Pharmacokinetic studies of various preparations of glyceryl trinitrate.

1 The pharmacokinetics and pharmacodynamics of five pharmaceutical preparations of glyceryl trinitrate (GTN) have been studied in six healthy volunteers. 2 Peak plasma GTN levels of 1.4 +/- 0.1 ng/ml were achieved at 3 min after sublingual administration (0.5 mg); 2.8 +/- 0.6 ng/ml and 2.5 +/- 0.3 ng/ml at 2 h and 4 h after Nitrocontin (6.4 mg) and Sustac (6.4 mg) respectively; 2.7 +/- 0.1 ng/ml and 2.5 +/- 0.2 ng/ml at 30 min after the cream (23 mg) and ointment (35 mg) respectively. 3 The mean times to reach half peak plasma GTN levels were 4.2 +/- 0.7 min after sublingual GTN, 6.5 +/- 0.9 h after Nitrocontin, 4.1 +/- 0.7 h after Sustac, 46.1 +/- 10.2 min after the ointment and 50.2 +/- 39.2 min after the cream. 4 Plasma nitrate (NO3) levels were undetectable after sublingual administration; peak NO3 levels were 0.48 +/- 0.03 microgram/ml at 4 h after Nitrocontin, 0.45 +/- 0.02 microgram/ml at 6 h after Sustac, 0.68 +/- 0.04 microgram/ml at 6 h (end of study) after the ointment and 0.63 microgram/ml at 4 h after the cream. 5 Plasma nitrite (NO2) was undetectable after sublingual GTN and peak NO2 levels were 0.48 +/- 0.04 microgram/ml at 2 h after Nitrocontin, 0.48 +/- 0.02 microgram/ml at 2 h after Sustac, 0.69 +/- 0.02 microgram/ml at 1 h after the ointment and 0.64 +/- 0.02 microgram/ml at 1 h after the cream. 6 Blood pressure (BP) declined throughout the 11 min of the study after sublingual GTN but did not change significantly after Nitrocontin or Sustac. After the ointment and the cream BP fell to the lowest level 30-60 min after administration and remained low throughout the 6 h of the study. 7 Heart rate (HR) increased to a maximum 5 min after sublingual administration with no significant increase after Nitrocontin or Sustac. After the ointment and the cream HR increased gradually to a maximum 30-60 min after administration remaining high throughout the rest of the study.