Substance fact sheet
The background information page contains information and concepts that will be useful in understanding some of the issues surrounding the NPI. It is strongly recommended that you read this before reading the information presented below.
For an explanation of some of the terms used in this page, see the Glossary
| Substance name | Nitric acid |
| CASR number | 7697-37-2 |
| Molecular formula | HNO3 |
| Synonyms | Hydrogen Nitrate, Azotic acid, aqua fortis, red fuming acid, Nital, Nitryl Hydroxide |
Physical and chemical properties Physical properties: Nitric acid is a transparent, colourless or yellowish, corrosive liquid with an acrid or pungent odour., Melting Point (°C): -41.59 Boiling Point (°C): 121 Specific Gravity: 1.502 Vapour Density: 2-3.0 Chemical properties: |
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Common uses Nitric acid is used in a wide variety of chemical processes where cleaning, oxidising or etching is required, including making synthetic fibres, dying, electrical circuit board making, electroplating, explosives, laboratory chemicals, metal cleaning and etching, semiconductors, pharmaceutical manufacture. It is used in the manufacture of fertilisers and other organic chemicals, in the printing industry for photoengraving, in jewellery manufacturing, and for wet chemical etching. |
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Sources of emissions Point sources Released from industries producing, using or handling nitric acid, for example chemical plants, metal, electronic, printing, glass, rubber and plastics plants and industries. Where ever very high temperature combustion takes place in the atmosphere in the presence of nitrogen, oxygen and water. May be present in small amounts in some waste-water from intensive farm factories and other facilities which produce waste-water containing high level of nitrogen. Diffuse sources, and point sources included in aggregated emissions data May be present in exhaust gases from motor vehicles, the exhaust of incinerators or other chemical plants, or where these are in contact with moisture in the air. Unlikely to persist in nature because it readily reacts with a wide variety of naturally occurring substances. Natural sources Rare in nature as a gas in the atmosphere, in groundwater around active volcanic regions, or drainage from areas where accumulated organic or animal wastes are present. Mobile sources Exhaust chambers in motor vehicles. Consumer products which may contain Nitric acid Could be retained as small amounts in products where it has been used in the manufacturing or treatment process. |
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Health effects How might I be exposed to Nitric acid? Most people are exposed outdoors to very minute amounts of nitric acid derived from exhaust fumes or the burning of some organic compounds that contain nitrogen. It is also present in small quantities in rain from areas where nitric oxide (a product of combustion) reacts with ozone and water to form nitric acid. People living near industries that produce or use nitric acid may be exposed to minute quantities of the compound as a result of low rates of emission. Nitric acid may form in minute amounts wherever very high temperatures are generated in the presence of air (nitrogen and oxygen) and water. By what pathways might Nitric acid enter my body? Trace amounts of nitric acid are present in the air circulating in and around major cities. It may be absorbed in minute amounts by inhaling it as a vapour. or swallowing it in liquid form. Relative health hazard On a health hazard spectrum of 0 - 3 Nitric acid registers 1.8. A score of 3 represents a very high hazard to health, 2 represents a medium hazard and 1 is harmful to health. Factors that are taken into account to obtain this ranking include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the evaluation of its tendency to cause, or not cause cancer and/or birth defects. It does not take into account exposure to the substance. Human exposure is reflected in the NPI rank given to this substance (see comparative data below). A substance that scores highly as a health hazard is arsenic at 2.3 and one of the lowest scores is ammonia at 1.0.  Health guidelines Worksafe Australia: Human exposure to nitric acid should be a time weighted average of less than 5.2 milligrams per cubic metre of air in an 8 hour period. Short term exposure over a 15 minute period of no more than 10 mg/m3 air is recommended. See the Additional Information page for current health information. The Australian NOHSC National Exposure Standards Database link is probably the most useful source of information. Note that the emissions data in the NPI database is not directly comparable with these guidelines. What effect might Nitric acid have on my health? Nitric acid is very corrosive compound. The vapour is very irritating to the eyes, throat, lungs and corrosive to the teeth. If the vapour is inhaled in significant amounts it will result in severe coughing, chest pain and shortness of breath. Contact with the skin will result in a severe corrosive burn. |
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Environmental effects Environmental Fate In the atmosphere, nitric acid is present in very minute quantities as a gas or vapour. It reacts with ammonia in the atmosphere to form a nitrate compound that is unlikely to persist for more than 10 to 15 days. Nitric acid does not build up in plant or animal tissues largely because of its highly reactive properties. In a concentrated form, nitric acid reacts very quickly with many other commonly occurring natural or manufactured substances and compounds. In some cases this can produce a vigorous reaction in the form of a chemical fire or explosion. Environmental Transport Nitric acid exists in the atmosphere in the gas phase. The atmospheric removal processes for gaseous nitric acid are by wet and dry deposition. The estimated half-life and lifetime for dry deposition of nitric acid is 1.5 to 2 days and 2 to 3 days, respectively, and efficient rain out during episodic precipitation events. Nitric acid reacts with gaseous ammonia to form particulate or aerosol nitrate, which in turn is removed by wet and dry deposition of the particles. The average half-life and lifetime for particles in the atmosphere is about 3.5 to 10 days and 5 to 15 days, respectively. Relative hazard to the environment On an environmental spectrum of 0 - 3 Nitric acid registers 0.8. A score of 3 represents a very high hazard to the environment and 0 a negligible hazard. Factors that are taken into account to obtain this ranking include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the measure of its ability to remain active in the environment and whether it accumulates in living organisms. It does not take into exposure to the substance. Environmental exposure is reflected in the NPI rank for this substance (see comparative data below). A substance that scores highly as an environmental hazard is oxides of nitrogen at 3.0 and one of the lower scores is carbon monoxide at 0.8.  Environmental guidelines See the Additional Information page for current environmental guidelines. No national guideline for nitric acid What effect might Nitric acid have on the environment? Nitric acid is a very corrosive compound when in concentrated form such as that commonly used in industrial and chemical processes. It is present in nature in very minute amounts. Severe thunderstorms can produce temperatures high enough to generate nitrogen dioxide which combines with water to form nitric acid. This is either rained or washed out of the atmosphere in very low concentrations. Nitric acid from this source readily reacts with ammonia in the atmosphere to form ammonium nitrate. |
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Comparative data NPI Rank Approximately 400 substances were considered for inclusion on the NPI reporting list. A risk ranking was given based on health and environmental hazard identification and human and environmental exposure to the substance. Some substances were grouped together at the same rank with 208 ranks in total. Nitric acid was ranked as 43 out of the 208 ranks. Total hazard score (human health + environmental criteria) = 2.6.  |
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Sources of information used in preparing this fact sheet
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