Ammonia is a colorless alkaline gas with a characteristic sharp smell. Ammonia is one of the most abundant nitrogen-containing compounds in the atmosphere. It is an irritant with a characteristic pungent odor, which is widely used in industry. Inasmuch as ammonia is highly soluble in water and, upon inhalation, is deposited in the upper airways, occupational exposures to ammonia have commonly been associated with sinusitis, upper airway irritation, and eye irritation. Acute exposures to high levels of ammonia have also been associated with diseases of the lower airways and interstitial lung. Ammonia has been shown to be a neurotoxin that predominantly affects astrocytes. Disturbed mitochondrial function and oxidative stress, factors implicated in the induction of the mitochondrial permeability transition, appear to be involved in the mechanism of ammonia neurotoxicity. Ammonia is formed in nearly all tissues and organs of the vertebrate organism; it is the most common endogenous neurotoxic compounds. Ammonia can affect the glutamatergic and GABAergic neuronal systems, the two prevailing neuronal systems of the cortical structures. Ammonia is well recognized to be central in the pathogenesis of hepatic encephalopathy and has been of importance to generations dating back to the early Egyptians. The gut produces ammonia which is metabolized in the liver and almost all organ systems are involved in ammonia metabolism. Colonic bacteria produce ammonia by splitting urea and other amino acids, however this does not explain hyperammonemia and hepatic encephalopathy. The alternative explanation is that hyperammonemia is the result of intestinal breakdown of amino acids, especially glutamine. The intestines have significant glutaminase activity, predominantly located in the enterocytes. On the other hand, this organ has only a little glutamine synthetase activity, making it a major glutamine-consuming organ. In addition to the intestine, the kidney is an important source of blood ammonia in patients with liver disease. Ammonia is also taken up by the muscle and brain in hepatic coma, and there is confirmation that ammonia is metabolized in muscle. The excessive formation of ammonia in the brains of Alzheimer's disease patients has been demonstrated, and it has been shown that some Alzheimer's disease patients exhibit elevated blood ammonia concentrations. Ammonia is the most important natural modulator of lysosomal protein processing: there is evidence for the involvement of aberrant lysosomal processing of beta-amyloid precursor protein (beta-APP) in the formation of amyloid deposits. Inflammatory processes and activation of microglia are widely believed to be implicated in the pathology of Alzheimer's disease. Ammonia is able to affect the characteristic functions of microglia, such as endocytosis, and cytokine production. Based on these facts, an ammonia-based hypothesis for Alzheimer's disease has been suggested. (6, 7, 8, 9, 10).
belongs to the class of inorganic compounds known as homogeneous other non-metal compounds. These are inorganic non-metallic compounds in which the largest atom belongs to the class of 'other non-metals'.
The topical damage caused by ammonia is probably due mainly to its alkaline properties. Its high water solubility allows it to dissolve in moisture on the mucous membranes, skin, and eyes, forming ammonium hydroxide. Ammonium hydroxide causes saponification of cell membrane lipids, resulting in cell disruption and death. Additionally, it extracts water from the cells and initiates an inflammatory response, which further damages the surrounding tissues. Excess circulating levels of ammonia (hyperammonemia) can cause serious neurological effects. This is thought to involve the alteration of glutamate metabolism in the brain and resultant increased activation of NMDA receptors, which causes decreased protein kinase C-mediated phosphorylation of Na+/K+ ATPase, increased activity of Na+/K+ ATPase, and depletion of ATP. Ammonia can chemically interact with an internal thiolester bond of
complement 3 (C3). This causes a conformation change in C3, which activates the alternative complement pathway, causing the release of chemoattractants and the assembly of the membrane attack complex of complement. The altered C3 can also bind directly to phagocyte complement receptors, which causes the release of toxic oxygen species. (29)
Metabolism
Ammonia can be absorbed by inhalation and oral routes exposure, and also to a much lesser extent through the skin and eyes. Most of the inhaled ammonia is retained in the upper respiratory tract and is subsequently eliminated in expired air, while ingested ammonia is readily absorbed in the intestinal tract. Ammonia that reaches the circulation is widely distributed to all body compartments although substantial first pass metabolism occurs in the liver where it is transformed into urea and glutamine. Ammonia or ammonium ion reaching the tissues is taken up by glutamic acid, which participates in transamination and other reactions. Ammonia is mainly excreted in the urine. (29)
Toxicity Values
LD50: 350 mg/kg (Oral, Rat) (2)
LC50: 3360 mg/m3 over 1 hour (Inhalation, Mouse) (2)
Severe hyperammonemia is characterized by serum ammonia levels greater than 1000 μmol/L
Lethal Dose
2500 to 4500 ppm over 30 minutes for an adult human. (29)
No indication of carcinogenicity to humans (not listed by IARC).
Uses/Sources
Ammonia is used directly on farm crops, and is also a precursor to foodstuffs and fertilizers. It is also found in many household and industrial cleaners. (29)
Acute exposure to high levels of ammonia in air may be irritating to skin, eyes, throat, and lungs and cause coughing and burns. Lung damage and death may occur after exposure to very high concentrations of ammonia. Swallowing concentrated solutions of ammonia can cause burns in mouth, throat, and stomach. Splashing ammonia into eyes can cause burns and even blindness. (29)
Chronically high levels of ammonia in the blood are associated with nearly 20 different inborn errors of metabolism including: 3-Hydroxy-3-Methylglutaryl-CoA Lyase Deficiency, Argininemia, Argininosuccinic Aciduria, Beta-Ketothiolase Deficiency, Biotinidase deficiency, Carbamoyl Phosphate Synthetase Deficiency, Carnitine-acylcarnitine translocase deficiency, Citrullinemia Type I, Hyperinsulinism-Hyperammonemia Syndrome, Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, Isovaleric Aciduria, Lysinuric Protein Intolerance, Malonic Aciduria, Methylmalonic Aciduria, Methylmalonic Aciduria Due to Cobalamin-Related Disorders, Propionic acidemia, Pyruvate carboxylase deficiency and Short Chain Acyl CoA Dehydrogenase Deficiency (SCAD Deficiency). Hyperammonemia is one of the metabolic derangements that contribute to hepatic encephalopathy.
Symptoms
Acute exposure leads to irritation and burning at the site of exposure. (29)
Symptoms include cough, chest pain (severe), chest tightness, difficulty breathing and wheezing, tearing and burning of eyes, temporary blindness, throat pain (severe), mouth pain, lip swelling, heart and blood, rapid, weak pulse, collapse and shock.
Chronic exposure: Symptoms of hyperammonia include: lethargy, irritability, poor feeding, vomiting and seizures. Signs and symptoms of late-onset hyperammonemia (later in life) may include intermittent ataxia, intellectual impairment, failure to thrive, gait abnormality, behavior disturbances, epilepsy, recurrent Reye syndrome and protein avoidance.
Treatment
Acute Exposure: EYES: irrigate opened eyes for several minutes under running water. INGESTION: do not induce vomiting. Rinse mouth with water (never give anything by mouth to an unconscious person). Seek immediate medical advice. SKIN: should be treated immediately by rinsing the affected parts in cold running water for at least 15 minutes, followed by thorough washing with soap and water. If necessary, the person should shower and change contaminated clothing and shoes, and then must seek medical attention. INHALATION: supply fresh air. If required provide artificial respiration.
Chronic Exposure: Intravenous arginine (argininosuccinase deficiency), sodium phenylbutyrate and sodium benzoate (ornithine transcarbamoylase deficiency) are pharmacologic agents commonly used as adjunctive therapy to treat hyperammonemia in patients.
Mohr, Rudolf. Ammonia separation from offgas obtained from melamine synthesis. U.S. (1971), 5 pp. CODEN: USXXAM US 3555784 19710119 CAN 77:50902 AN 1972:450902
