Nitrates & Nitrites PoisoningNitrates & Nitrites Poisoning

Arsalan KhanArsalan Khan

MPhil (Clinical Medicine & Surgery)MPhil (Clinical Medicine & Surgery)

2014-ag-14512014-ag-1451

University of Agriculture, Faisalabad University of Agriculture, Faisalabad PakistanPakistan

Nitrate Poisoning Nitrate Poisoning Nitrate toxicosisNitrate toxicosis can occur through enterohepatic  can occur through enterohepatic metabolism of nitrate. metabolism of nitrate.

Ruminants are especially vulnerable because the ruminal flora Ruminants are especially vulnerable because the ruminal flora reduces nitrate to ammonia, with nitrite as an intermediate reduces nitrate to ammonia, with nitrite as an intermediate product and nitrite is 10 times more toxic than nitrate.product and nitrite is 10 times more toxic than nitrate. Nitrites oxidize the iron atoms in hemoglobin fromNitrites oxidize the iron atoms in hemoglobin from

  ferrous iron (2+) to ferric iron (3+), rendering it unable to carry ferrous iron (2+) to ferric iron (3+), rendering it unable to carry oxygen.oxygen. This process can lead to generalized lack of This process can lead to generalized lack of oxygen in organ tissue and a dangerous condition called oxygen in organ tissue and a dangerous condition called methemoglobinemia.methemoglobinemia.

Although nitrite converts to ammonia, if there is more nitrite Although nitrite converts to ammonia, if there is more nitrite than can be converted, the animal slowly suffers from a lack of than can be converted, the animal slowly suffers from a lack of oxygen.oxygen.

MethemoglobinMethemoglobin  It is a form of the oxygen-carryingIt is a form of the oxygen-carrying

  metallo protein hemoglobin, in which the iron in metallo protein hemoglobin, in which the iron in the heme group is in the Fethe heme group is in the Fe3+3+ (ferric) state, not  (ferric) state, not the Fethe Fe2+2+ (ferrous) of normal hemoglobin.  (ferrous) of normal hemoglobin. Methemoglobin cannot bind oxygen, unlikeMethemoglobin cannot bind oxygen, unlike

oxyhemoglobin.oxyhemoglobin.

In human blood a trace amount of In human blood a trace amount of methemoglobin is normally produced methemoglobin is normally produced spontaneously, but when present in excess the spontaneously, but when present in excess the blood becomes abnormally dark bluish brown. blood becomes abnormally dark bluish brown.

An enzyme methemoglobin reductase is An enzyme methemoglobin reductase is responsible for converting methemoglobin back responsible for converting methemoglobin back to hemoglobin.to hemoglobin.

Methemoglobin is incapable of transporting Methemoglobin is incapable of transporting oxygen to various body tissues so the animal oxygen to various body tissues so the animal exhibits a characteristic chocolate brown blood exhibits a characteristic chocolate brown blood color prior to and during death which is caused color prior to and during death which is caused by asphyxiation. by asphyxiation.

Crops like barley, oat, corn, millet, sunflower, Crops like barley, oat, corn, millet, sunflower, sorghum etc have the high potential of nitrate sorghum etc have the high potential of nitrate accumulation.accumulation.

Nitrates are relatively non toxic to the animals Nitrates are relatively non toxic to the animals but they are converted to nitrites in the rumen but they are converted to nitrites in the rumen reduced by ruminal microflora.reduced by ruminal microflora.

Nirite oxidizes ferrous ion of heamoglobin to Nirite oxidizes ferrous ion of heamoglobin to ferric state producing brown pigment ferric state producing brown pigment methemoglobin; which is incapable of methemoglobin; which is incapable of transporting oxygen to the tissues. transporting oxygen to the tissues.

Toxicity occurs in animals grazing herbage Toxicity occurs in animals grazing herbage containing 0.7 grams nitrate/Kg DM.containing 0.7 grams nitrate/Kg DM.

Plant Factors in Nitrate Plant Factors in Nitrate Accumulation Accumulation

• Stalks are highest in nitrate content, followed in Stalks are highest in nitrate content, followed in order by leaves and grain in decreasing order by leaves and grain in decreasing amounts. amounts.

Immature or young plants have a greater Immature or young plants have a greater potential for nitrate accumulation than older potential for nitrate accumulation than older plants.plants.

Any weather condition which reduces plant Any weather condition which reduces plant growth may increase nitrate accumulation. This growth may increase nitrate accumulation. This includes drought and sometimes cool, cloudy includes drought and sometimes cool, cloudy weather.weather.

Excessive use of nitrogen fertilizer may Excessive use of nitrogen fertilizer may contribute to the problem. contribute to the problem.

Acid soils and phosphorus deficient soils will Acid soils and phosphorus deficient soils will increase plant nitrate accumulation. increase plant nitrate accumulation.

Nitrate Toxicity in the AnimalNitrate Toxicity in the Animal

Like plants, ruminant animals also use the Like plants, ruminant animals also use the nitrogen in nitrates to make protein. Conversion is nitrogen in nitrates to make protein. Conversion is made by bacteria in the rumen. Nitrite, one of the made by bacteria in the rumen. Nitrite, one of the intermediate products in this conversion, is the intermediate products in this conversion, is the cause of nitrate poisoning. Nitrate toxicity occurs cause of nitrate poisoning. Nitrate toxicity occurs when high nitrate levels in the feed overwhelm the when high nitrate levels in the feed overwhelm the animal’s digestive system to the extent that the animal’s digestive system to the extent that the rate of conversion of nitrate to nitrite is faster than rate of conversion of nitrate to nitrite is faster than the conversion of nitrite to ammonia (which is the conversion of nitrite to ammonia (which is incorporated into amino acids and protein). incorporated into amino acids and protein).

When this happens, nitrite accumulates When this happens, nitrite accumulates and is absorbed into the bloodstream. and is absorbed into the bloodstream. There, it reacts with the oxygen-carrying There, it reacts with the oxygen-carrying hemoglobin, changing it into a form hemoglobin, changing it into a form (methemoglobin) that cannot transport (methemoglobin) that cannot transport oxygen to the lungs and body tissues. The oxygen to the lungs and body tissues. The animal literally suffocates.animal literally suffocates.

Cattle are much more likely to be affected Cattle are much more likely to be affected than sheep or horses.than sheep or horses.

A total intake of 30 to 45 grams of nitrate ion A total intake of 30 to 45 grams of nitrate ion per 50 Kg of body weight is considered per 50 Kg of body weight is considered acutely toxic in normal animals. acutely toxic in normal animals.

However, intakes of 8 to 22 grams per 50 Kg However, intakes of 8 to 22 grams per 50 Kg of body weight may be toxic when animals of body weight may be toxic when animals are ill or undergoing an abrupt diet change.are ill or undergoing an abrupt diet change.

Nitrate poisoning acts very quickly, and symptoms Nitrate poisoning acts very quickly, and symptoms may not be observed before animals are found may not be observed before animals are found dead. Animals being poisoned may stand apart dead. Animals being poisoned may stand apart from the herd, then collapse, or they may fall in from the herd, then collapse, or they may fall in their tracks if driven. their tracks if driven.

Signs of poisoning, in the usual order of Signs of poisoning, in the usual order of appearance, are weakness and unsteady gait, appearance, are weakness and unsteady gait, collapse, shallow and rapid breathing, rapid pulse, collapse, shallow and rapid breathing, rapid pulse, coma, and death—the latter accompanied by the coma, and death—the latter accompanied by the usual terminal muscular reflex movements.usual terminal muscular reflex movements.

Symptoms

Dyspnoea (difficult breathing) becomes Dyspnoea (difficult breathing) becomes progressively more severeprogressively more severe

Respiratory distress—mouth breathing, Respiratory distress—mouth breathing,

Violent respiratory movements, and extreme Violent respiratory movements, and extreme apprehension—are observed. apprehension—are observed.

A rapid and weak heart beat, A rapid and weak heart beat,

Subnormal body temperature, Subnormal body temperature,

Muscular weakness, Muscular weakness,

Frequent urinationFrequent urination

Loss of muscular coordination (staggering gait and Loss of muscular coordination (staggering gait and muscular tremors), muscular tremors),

Blue discoloration of mucous membranes,Blue discoloration of mucous membranes,

And marked dilation of pupils follow initial And marked dilation of pupils follow initial observed symptoms. observed symptoms.

Brownish discoloration of the blood is Brownish discoloration of the blood is characteristic of nitrate poisoning.characteristic of nitrate poisoning.

Death may occur within 1 hour or, in the usual Death may occur within 1 hour or, in the usual case, within 3 to 4 hours of the onset of difficult case, within 3 to 4 hours of the onset of difficult breathing.breathing.

Subacute or chronic nitrate poisoning may result in Subacute or chronic nitrate poisoning may result in reproductive problems, including abortions. reproductive problems, including abortions.

Nitrate Tests Nitrate Tests

Brown ring test:Brown ring test:

A common nitrate test, known as the A common nitrate test, known as the brown ring brown ring testtest can be performed by adding Ferrous  can be performed by adding Ferrous sulfate to a solution of a nitrate, then slowly sulfate to a solution of a nitrate, then slowly adding concentrated sulphuric acid such that the adding concentrated sulphuric acid such that the acid forms a layer below the aqueous solution. A acid forms a layer below the aqueous solution. A brown ring will form at the junction of the two brown ring will form at the junction of the two layers, indicating the presence of the nitrate ion.layers, indicating the presence of the nitrate ion.

  The overall reaction is the The overall reaction is the reductionreduction of the  of the nitrate ion by ferrous ion which is oxidised to nitrate ion by ferrous ion which is oxidised to ferric ion and formation of a nitrosonium complex ferric ion and formation of a nitrosonium complex where nitric oxide is oxidised to NOwhere nitric oxide is oxidised to NO++..

NONO33-- + 3Fe + 3Fe2+2+ + 4H + 4H++ → 3Fe → 3Fe3+3+ + NO + 2H + NO + 2H22OO

[Fe(H[Fe(H22O)O)66]]2+2+ + NO → [Fe(H + NO → [Fe(H22O)O)55(NO)](NO)]2+2+ + H + H22OO

Diphenylamine testDiphenylamine test

Diphenylamine may be used as a chemical Diphenylamine may be used as a chemical test for the presence of the nitrate ion. In this test for the presence of the nitrate ion. In this test, a solution of diphenylamine and ammonium test, a solution of diphenylamine and ammonium chloride in sulfuric acid is used. In the presence chloride in sulfuric acid is used. In the presence of nitrates, diphenylamine is oxidized, giving a of nitrates, diphenylamine is oxidized, giving a blue coloration.blue coloration.

TreatmentTreatment

• Handle poisoned animals quietly. Handle poisoned animals quietly. • Administer Methylene blue intravenously. Administer Methylene blue intravenously. • Use 1- to 4-percent solution containing 5 percent Use 1- to 4-percent solution containing 5 percent

dextrose at the rate of 1 gram of methylene blue dextrose at the rate of 1 gram of methylene blue for each 100kg of body weight for each 100kg of body weight

• Or 1% methylene blue in distilled water or Or 1% methylene blue in distilled water or isotonic saline at 4–22 mg/kg depending on isotonic saline at 4–22 mg/kg depending on severity of exposure.severity of exposure.

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