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 | Phosphoric acid |
| CASR number | 7664-38-2 |
| Molecular formula | H3O4P (or PO(OH)3) |
| Synonyms | Orthophosphoric acid, white phosphoric acid, Sonac |
Physical and chemical properties Physical properties: Pure phosphoric acid is a non-combustible, colourless, odourless and hygroscopic crystal. Commercial phosphoric acid comes as a viscous solution in water which contains 75-85% phosphoric acid. The liquid can solidify at lower temperatures. Melting Point (°C): 42 (pure), 21 (85%), 18 (75%) Boiling Point (°C): 260 (pure), 154 (85%), 135 (75%) Specific Gravity: 1.88 (pure), 1.69 (85%), 1.58 (75%) Vapour Density: 3.4 (pure) Chemical properties: |
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Common uses Phosphoric acid is used in the manufacture of superphosphate fertilisers, livestock feeds, phosphate salts, polyphosphates, soaps, waxes, polishes and detergents. Phosphoric acid is used as a soil stabiliser, in the manufacture of fire control agents, opal glasses, electric lights, in cotton dyeing, tile cleaning, ceramic binding, dental cement, water treatment, electro-polishing, operating lithography, photoengraving operations, process engraving, as a petrol additive and in coagulating rubber latex. It is used in metal rust proofing before painting, in the polishing of metals, in pickling and in hot stripping for aluminium and zinc substrates. Phosphoric acid is used as an acid catalyst in making ethylene and purifying hydrogen peroxide, in the manufacture of chemicals (ethylbenzene, propylene, cumene), as a bonding agent for refractory bricks, in extracting penicillin and as an analytical agent. It is used as an anti-oxidant in food, as a flavour additive for sharp taste in food (jellies, preserves) and soft drinks (e.g. Coca-Cola), as a tang (Food Additive 338) and for the manufacture of yeasts and gelatine. It is used to manufacture the phosphoric acid electrolyte fuel cell system and it has been used to treat lead poisoning. |
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Sources of emissions Point sources It may enter the environment from industrial discharges, spills or mining operations run-off. Diffuse sources, and point sources included in aggregated emissions data Sub-threshold facilities. Natural sources Phosphoric acid is not directly found in nature. It can be obtained from phosphate rock deposits. Mobile sources There are no mobile sources for phosphoric acid. Consumer products which may contain Phosphoric acid Phosphoric acid can be found in soft drinks (e.g. Coca-Cola), food (e.g. jellies, preserves), animal food (e.g. cat food), some cleaning agents. |
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Health effects How might I be exposed to Phosphoric acid? Occupational exposure to concentrated levels of phosphoric acid may occur in industries manufacturing and using phosphoric acid. The general public may be exposed to small quantities of phosphoric acid in the consumption of food and soft drinks and by using some cleaning agents. By what pathways might Phosphoric acid enter my body? The substance can be absorbed into the body by inhalation of its aerosol and by ingestion. Relative health hazard On a health hazard spectrum of 0 - 3 Phosphoric acid registers 1.2. 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 has set the exposure standard for phosphoric acid to 1 milligram/m33 (TWA). The short-term exposure level (STEL) is 3 milligram/m3. 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 Phosphoric acid have on my health? Phosphoric acid can severely affect human health through the inhalation of mist, ingestion and contact with skin and eyes. Eye contact can cause redness, pain, tearing, eyelid spasms, blurred vision and permanent damage. Phosphoric acid can attack the mucous membranes of the mouth, throat and oesophagus, leading to immediate pain and difficulty in swallowing (dysphagia). Other symptoms of phosphoric acid poisoning include a sour acrid taste, coughing, difficult breathing, conjunctivitis, severe gastrointestinal irritation, nausea, vomiting, bloody diarrhoea, severe abdominal pains, extreme thirst, convulsion, shock and even death through choking (asphyxia). Higher phosphoric acid levels can cause a build-up of fluid in the lungs (pulmonary oedema) which may result in death. It can cause circulatory collapse with clammy skin, weak and rapid pulse, shallow respiration and scanty urine. Repeated exposure to phosphoric acid can cause bronchitis with cough, phlegm and/or shortness of breath. Long-term skin exposure to the liquid may cause dermatitis. People at special risk of exposure to phosphoric acid include those with chronic pulmonary disease or skin disease. |
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Environmental effects Environmental Fate Phosphoric acid entering the environment can acidify soils and waters. Smaller quantities of phosphoric acid will be neutralised forming harmless phosphate salts or it will be diluted to harmless levels. Environmental Transport Phosphoric acid can be transported as mist in air and dissolved in water. Relative hazard to the environment On an environmental spectrum of 0 - 3 Phosphoric acid registers 1. 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 Australian Water Quality Guidelines for Fresh and Marine Waters: (ANZECC, 1992): Total phosphate: 10 to 100 micrograms/L (ie 0.00001 to 0.0001g/L) See the Additional Information page for current environmental guidelines. Note that the emissions data in the NPI database is not directly comparable with these guidelines. What effect might Phosphoric acid have on the environment? Phosphoric acid has moderate acute and chronic toxicity to aquatic life in waters of low alkalinity. Whilst small quantities of phosphoric acid can be neutralised by the alkalinity in aquatic ecosystems, larger quantities can lower the pH for extended periods of time, posing a potential risk to aquatic organisms. Phosphate (formed when phosphoric acid is dissolved) is unlikely to bioaccumulate in most aquatic species. Insufficient data are available to evaluate or predict the short-term and long-term effects of phosphoric acid on plants, birds or land animals. |
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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. Phosphoric acid was ranked as 38 out of the 208 ranks. Total hazard score (human health + environmental criteria) = 2.2.  |
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Sources of information used in preparing this article
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