• Neurotoxic

• 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. (L958)
• 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. (L958)
• Health Effects: 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. (L958) 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. (L958) 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.
• Route of Exposure: Oral (L958) ; inhalation (L958) ; dermal (L958)

• Carcinogenicity: No indication of carcinogenicity to humans (not listed by IARC).
• Toxicity: LD50: 350 mg/kg (Oral, Rat) (A591) LC50: 3360 mg/m3 over 1 hour (Inhalation, Mouse) (A591) 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. (L958)
• Minimum Risk Level: Acute Inhalation: 1.7 ppm (L134) Chronic Inhalation: 0.1 ppm (L134)

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. (L958)