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Nitrate

From Wikipedia, the free encyclopedia
For the functional group –ONO
2,seeNitrate ester.For that functional group in medicine, seeNitrovasodilator.
Not to be confused withNO−
2,nitrite.
This article is about the ion. For the radical, seenitrate radical.
For other uses, seeNitrate (disambiguation).
Nitrate
Ball-and-stick model of the nitrate ion
Names
Systematic IUPAC name
Nitrate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
UNII
  • InChI=1S/NO3/c2-1(3)4/q-1
    Key: NHNBFGGVMKEFGY-UHFFFAOYSA-N
  • InChI=1/NO3/c2-1(3)4/q-1
    Key: NHNBFGGVMKEFGY-UHFFFAOYAI
  • [N+](=O)([O-])[O-]
Properties
NO−
3
Molar mass 62.004g·mol−1
Conjugate acid Nitric acid
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).

Nitrateis apolyatomic ionwith thechemical formulaNO−
3.Saltscontaining thisionare callednitrates.Nitrates are common components of fertilizers and explosives.[1]Almost all inorganic nitrates aresolubleinwater.An example of an insoluble nitrate isbismuth oxynitrate.

Chemical structure[edit]

The nitrate ion with the partial charges shown

The nitrateanionis theconjugate baseofnitric acid,consisting of one centralnitrogenatomsurrounded by three identically bondedoxygenatoms in atrigonal planararrangement. The nitrate ion carries aformal chargeof −1.[citation needed]This charge results from a combination formal charge in which each of the three oxygens carries a −2⁄3charge,[citation needed]whereas the nitrogen carries a +1 charge, all these adding up to formal charge of the polyatomic nitrate ion.[citation needed]This arrangement is commonly used as an example ofresonance.Like theisoelectroniccarbonateion, the nitrate ion can be represented by three resonance structures:

Canonical resonance structures for the nitrate ion

Chemical and biochemical properties[edit]

In theNO−3anion, theoxidation stateof the central nitrogen atom is V (+5). This corresponds to the highest possibleoxidation numberof nitrogen. Nitrate is a potentially powerfuloxidizeras evidenced by itsexplosivebehaviour at high temperature when it isdetonatedinammonium nitrate(NH4NO3), orblack powder,ignited by theshock waveof aprimary explosive.However, in contrast tored fuming nitric acid(HNO3/N2O4), or concentratednitric acid(HNO3), nitratedissolvedinaqueous solutionat neutral or highpHis only a weakoxidizing agentand is stable under sterile, oraseptic,conditions, in the absence ofmicroorganisms.To increase its oxidation power, acidic conditions and high concentrations are needed, under which nitrate transforms into nitric acid. This behaviour is consistent with the general theory ofreduction-oxidation(redox) inelectrochemistry:oxidizing power is exacerbated under acidic conditions while the power ofreducing agentsis reinforced under basic conditions. This can be illustrated by means of aPourbaix diagram(Eh–pH diagram) drawn using theNernst equationand the corresponding redox reactions. During the reduction of oxidizers, the oxidation state decreases andoxide ions(O2−) in excess released in water by the reaction are more easilyprotonatedunder acid conditions (O2−+ 2 H+→ H2O) which drives the reduction reaction to the right according toLe Chatelier's principle.For the oxidation of reducing agents, the reverse occurs: as the oxidation state increases, oxide anions are needed to neutralise the surplus of positive charges born by the central atom. As basic conditions favor the production of oxide anions (2 OH−→ O2−+ H2O), this drives thechemical equilibriumof the oxidation reaction to the right.

Meanwhile, nitrate is used as a powerful terminalelectron acceptorbydenitrifying bacteriato deliver the energy they need to thrive. Underanaerobic conditions,nitrate is the strongest electron acceptor used byprokaryotemicroorganisms(bacteriaandarchaea) to respirate. TheredoxcoupleNO−3/N2is at the top of theredox scalefor theanaerobic respiration,just below the couple oxygen (O2/H2O), but above the couples Mn(IV)/Mn(II), Fe(III)/Fe(II),SO2−4/HS−,CO2/CH4.In natural waters, inevitably contaminated by microorganisms, nitrate is a quite unstable and labile dissolved chemical species because it ismetabolisedby denitrifying bacteria. Water samples for nitrate/nitrite analyses need to be kept at 4 °C in a refrigerated room and analysed as quick as possible to limit the loss of nitrate.

In the first step of the denitrification process, dissolved nitrate (NO−3) iscatalyticallyreducedinto nitrite (NO−2) by theenzymatic activityof bacteria. In aqueous solution, dissolved nitrite, N(III), is a more powerful oxidizer that nitrate, N(V), because it has to accept lesselectronsand itsreductionis lesskineticallyhindered than that of nitrate.

During the biological denitrification process, further nitrite reduction also gives rise to another powerful oxidizing agent:nitric oxide(NO). NO can fix onmyoglobinaccentuating its red coloration. NO is an important biologicalsignaling moleculeand intervenes in thevasodilationprocess, but it can also producefree radicalsinbiological tissues,accelerating their degradation and aging process. Thereactive oxygen species(ROS) generated by NO contribute to theoxidative stress,a condition involved in vascular dysfunction andatherogenesis.[2]

Detection in chemical analysis[edit]

The nitrateanionis commonly analysed in water byion chromatography(IC) along with other anions also present in solution. The main advantage of IC is its ease and the simultaneousanalysisof all the anions present in the aqueous sample. Other methods for the specific detection of nitrate rely on its conversion to nitrite followed by nitrite-specific tests. Thereductionof nitrate to nitrite is effected by acopper-cadmiummaterial. The sample is introduced in aflow injection analyzer,and the resulting nitrite-containing effluent is then combined with a reagent for colorimetric or electrochemical detection. The most popular of these assays is theGriess test,whereby nitrite is converted to a deeply coloredazo dyesuited for UV-vis spectroscopic analysis. The method exploits the reactivity ofnitrous acidderived from acidification of nitrite. Nitrous acid selectively reacts with aromatic amines to give diazonium salts, which in turn couple with a second reagent to give the azo dye. Thedetection limitis 0.02 to 2 μM.[3]Such methods have been highly adapted to biological samples.[4]

Occurrence and production[edit]

Nitrate salts are found naturally on earth in arid environments as large deposits, particularly ofnitratine,a major source ofsodium nitrate.

Nitrates are produced by a number of species ofnitrifying bacteriain the natural environment usingammoniaorureaas a source of nitrogen and source of free energy. Nitrate compounds forgunpowderwere historically produced, in the absence of mineral nitrate sources, by means of variousfermentationprocesses using urine and dung.

Lightning strikes in earth's nitrogen- and oxygen-rich atmosphere produce a mixture of oxides of nitrogen, which formnitrousions and nitrate ions, which are washed from the atmosphere by rain or inoccult deposition.

Nitrates are produced industrially fromnitric acid.[1]

Uses[edit]

Agriculture[edit]

Nitrate is achemical compoundthat serves as a primary form of nitrogen for many plants. This essential nutrient is used by plants to synthesize proteins, nucleic acids, and other vital organic molecules.[5]The transformation of atmospheric nitrogen into nitrate is facilitated by certain bacteria and lightning in the nitrogen cycle, which exemplifies nature's ability to convert a relatively inert molecule into a form that is crucial for biological productivity.[6]

Nitrates are used asfertilizersinagriculturebecause of their high solubility and biodegradability. The main nitrate fertilizers areammonium,sodium,potassium,calcium,andmagnesiumsalts. Several billion kilograms are produced annually for this purpose.[1]The significance of nitrate extends beyond its role as a nutrient since it acts as a signaling molecule in plants, regulating processes such as root growth, flowering, and leaf development.[7]

While nitrate is beneficial for agriculture since it enhances soil fertility and crop yields, its excessive use can lead to nutrient runoff, water pollution, and the proliferation of aquatic dead zones.[8]Therefore, sustainable agricultural practices that balance productivity with environmental stewardship are necessary. Nitrate's importance in ecosystems is evident since it supports the growth and development of plants, contributing to biodiversity and ecological balance.[9]

Firearms[edit]

Nitrates are used as oxidizing agents, most notably in explosives, where the rapid oxidation of carbon compounds liberates large volumes of gases (seegunpowderfor an example).

Industrial[edit]

Sodium nitrate is used to remove air bubbles from molten glass and some ceramics. Mixtures of the molten salt are used to harden some metals.[1]

Photographic film[edit]

Nitrate was also used as afilm stockthroughnitrocellulose.Due to its high combustibility, thefilm makingstudios swapped tocellulose acetatesafety film in 1950.

Medicinal and pharmaceutical use[edit]

In the medical field, nitrate-derived organicesters,such asglyceryl trinitrate,isosorbide dinitrate,andisosorbide mononitrate,are used in the prophylaxis and management ofacute coronary syndrome,myocardial infarction,acute pulmonary oedema.[10]This class of drug, to whichamyl nitritealso belongs, is known asnitrovasodilators.

Toxicity and safety[edit]

The two areas of concerns about the toxicity of nitrate are the following:

Methemoglobinemia[edit]

Main articles:Blue baby syndromeandMethemoglobinemia

One of the most common cause ofmethemoglobinemiain infants is due to the ingestion of nitrates and nitrites throughwell wateror foods.

In fact, nitrates (NO−3), often present at too highconcentrationin drinkwater, are only the precursor chemical species ofnitrites(NO−2), the real culprits of methemoglobinemia. Nitrites produced by themicrobial reduction of nitrate(directly in the drinkwater, or after ingestion by the infant, in his digestive system) are more powerfuloxidizersthan nitrates and are the chemical agent really responsible for theoxidationof Fe2+into Fe3+in thetetrapyrrolehemeofhemoglobin.Indeed, nitrate anions are too weak oxidizers inaqueous solutionto be able to directly, or at least sufficiently rapidly, oxidize Fe2+into Fe3+,because ofkineticslimitations.

Infants younger than 4 months are at greater risk given that they drink more water per body weight, they have a lowerNADH-cytochrome b5 reductaseactivity, and they have a higher level of fetal hemoglobin which converts more easily tomethemoglobin.Additionally, infants are at an increased risk after an episode ofgastroenteritisdue to the production ofnitritesbybacteria.[13]

However, other causes than nitrates can also affect infants and pregnant women.[14][15]Indeed, theblue baby syndromecan also be caused by a number of other factors such as thecyanotic heart disease,acongenital heart defectresulting in low levels of oxygen in the blood,[16]or by gastric upset, such as diarrheal infection, protein intolerance, heavy metal toxicity, etc.[17]

Drinking water standards[edit]

Through theSafe Drinking Water Act,theUnited States Environmental Protection Agencyhas set a maximum contaminant level of 10 mg/L or 10 ppm of nitrate in drinking water.[18]

An acceptable daily intake (ADI) for nitrate ions was established in the range of 0–3.7 mg (kg body weight)−1day−1by the Joint FAO/WHO Expert Committee on Food Additives (JEFCA).[19]

Aquatic toxicity[edit]

Sea surface nitrate from theWorld Ocean Atlas

Infreshwaterorestuarinesystems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia,[20]levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.[21]Nitrate toxicity remains a subject of debate.[22]

In most cases of excess nitrate concentrations in aquatic systems, the primary sources are wastewater discharges, as well assurface runofffrom agricultural orlandscapedareas that have received excess nitrate fertilizer. The resultingeutrophicationand algae blooms result inanoxiaanddead zones.As a consequence, as nitrate forms a component oftotal dissolved solids,they are widely used as an indicator ofwater quality.

Human Impacts on Ecosystems through Nitrate Deposition[edit]

Excessive use of nitrate from theNitrate and Phosphate Pacific Ocean

Nitrate deposition into ecosystems has markedly increased due to anthropogenic activities, notably from the widespread application of nitrogen-rich fertilizers in agriculture and the emissions from fossil fuel combustion.[23]Annually, about 195 million metric tons of synthetic nitrogen fertilizers are used worldwide, with nitrates constituting a significant portion of this amount.[24]In regions with intensive agriculture, such as parts of the U.S., China, and India, the use of nitrogen fertilizers can exceed 200 kilograms per hectare.[24]

The impact of increased nitrate deposition extends beyond plant communities to affect soil microbial populations.[25]The change in soil chemistry and nutrient dynamics can disrupt the natural processes of nitrogen fixation, nitrification, and denitrification, leading to altered microbial community structures and functions. This disruption can further impact the nutrient cycling and overall ecosystem health.[26]

Dietary nitrate[edit]

A source of nitrate in the human diets arises from the consumption of leafy green foods, such asspinachandarugula.NO−
3can be present inbeetrootjuice. Drinking water represents also a primary nitrate intake source.[27]

Nitrate ingestion rapidly increases theplasmanitrate concentration by a factor of 2 to 3, and this elevated nitrate concentration can be maintained for more than 2 weeks. Increased plasma nitrate enhances the production ofnitric oxide,NO. Nitric oxide is a physiological signaling molecule which intervenes in, among other things, regulation of muscle blood flow and mitochondrial respiration.[28]

Cured meats[edit]

Nitrite(NO−2) consumption is primarily determined by the amount ofprocessed meatseaten, and the concentration of nitrates (NO−3) added to these meats (bacon,sausages…) for their curing. Althoughnitritesare the nitrogen species chiefly used inmeat curing,nitrates are used as well and can be transformed into nitrite by microorganisms, or in the digestion process, starting by their dissolution insalivaand their contact with themicrobiotaof the mouth. Nitrites lead to the formation ofcarcinogenicnitrosamines.[29]The production of nitrosamines may be inhibited by the use of theantioxidantsvitamin Cand theAlpha -tocopherolform ofvitamin Eduring curing.[30]

Many meat processors claim their meats (e.g. bacon) is "uncured" – which is a marketing claim with no factual basis: there is no such thing as "uncured" bacon (as that would be, essentially, raw sliced pork belly).[31][better source needed]"Uncured" meat is in fact actually cured with nitrites with virtuallynodistinction in process – the only difference being the USDA labeling requirement between nitrite of vegetable origin (such as from celery) vs. "synthetic" sodium nitrite. An analogy would be purified "sea salt"vs.sodium chloride– both being exactly the same chemical with the only essential difference being the origin.

Anti-hypertensivediets, such as theDASH diet,typically contain high levels of nitrates, which are first reduced tonitritein thesaliva,as detected insaliva testing,prior to formingnitric oxide(NO).[27]

Domestic animal feed[edit]

Symptoms of nitrate poisoning in domestic animals include increased heart rate and respiration; in advanced cases blood and tissue may turn a blue or brown color. Feed can be tested for nitrate; treatment consists of supplementing or substituting existing supplies with lower nitrate material. Safe levels of nitrate for various types of livestock are as follows:[32]

Category %NO3 %NO3–N %KNO3 Effects
1 < 0.5 < 0.12 < 0.81 Generally safe for beef cattle and sheep
2 0.5–1.0 0.12–0.23 0.81–1.63 Caution: some subclinical symptoms may appear in pregnant horses, sheep and beef cattle
3 1.0 0.23 1.63 High nitrate problems: death losses and abortions can occur in beef cattle and sheep
4 < 1.23 < 0.28 < 2.00 Maximum safe level for horses. Do not feed high nitrate forages to pregnant mares

The values above are on a dry (moisture-free) basis.

Salts and covalent derivatives[edit]

Nitrate formation with elements of the periodic table:

See also[edit]

References[edit]

  1. ^abcdLaue W, Thiemann M, Scheibler E, Wiegand KW (2006). "Nitrates and Nitrites".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.a17_265.ISBN978-3527306732.
  2. ^Lubos E, Handy DE, Loscalzo J (May 2008)."Role of oxidative stress and nitric oxide in atherothrombosis".Frontiers in Bioscience.13(13). IMR Press: 5323–5344.doi:10.2741/3084.PMC2617738.PMID18508590.
  3. ^Moorcroft MJ, Davis J, Compton RG (June 2001). "Detection and determination of nitrate and nitrite: a review".Talanta.54(5): 785–803.doi:10.1016/S0039-9140(01)00323-X.PMID18968301.
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  7. ^Liu B, Wu J, Yang S, Schiefelbein J, Gan Y (July 2020). Xu G (ed.)."Nitrate regulation of lateral root and root hair development in plants".Journal of Experimental Botany.71(15): 4405–4414.doi:10.1093/jxb/erz536.PMC7382377.PMID31796961.
  8. ^Bashir U, Lone FA, Bhat RA, Mir SA, Dar ZA, Dar SA (2020). "Concerns and Threats of Contamination on Aquatic Ecosystems". In Hakeem KR, Bhat RA, Qadri H (eds.).Bioremediation and Biotechnology.Cham: Springer International Publishing. pp. 1–26.doi:10.1007/978-3-030-35691-0_1.ISBN978-3-030-35690-3.
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  16. ^MedlinePlus Encyclopedia:Cyanotic heart disease
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  18. ^"4. What are EPA's drinking water regulations for nitrate?".Ground Water & Drinking Water.Retrieved2018-11-13.
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  21. ^Sharpe, Shirlie."Nitrates in the Aquarium".About.Archived fromthe originalon July 24, 2011.RetrievedOctober 30,2013.
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  29. ^Bingham SA, Hughes R, Cross AJ (November 2002)."Effect of white versus red meat on endogenous N-nitrosation in the human colon and further evidence of a dose response".The Journal of Nutrition.132(11 Suppl): 3522S–3525S.doi:10.1093/jn/132.11.3522S.PMID12421881.
  30. ^Parthasarathy DK, Bryan NS (November 2012). "Sodium nitrite: the" cure "for nitric oxide insufficiency".Meat Science.92(3): 274–279.doi:10.1016/j.meatsci.2012.03.001.PMID22464105.
  31. ^"Is There a Difference Between Cured and Uncured Bacon?".9 December 2022.
  32. ^"Nitrate Risk in Forage Crops - Frequently Asked Questions".Agriculture and Rural Development.Government of Alberta.RetrievedOctober 30,2013.

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