If you enjoy eating grain products such as cereals, you’re probably benefiting from phosphoric acid (at least indirectly) without even realising it. That’s because the compound is primarily used to manufacture phosphate fertilisers, which are integral to the agricultural industry as they help crops grow.
But that’s not its only use; phosphoric acid also has applications in the wider food industry. For example, it’s often used as a preservative, binding agent, and flavour enhancer.
Continue reading to learn more about the use of phosphoric acid in agriculture and food, as well as the associated health and environmental concerns.
In this post:
What is phosphoric acid?
At room temperature, pure phosphoric acid is a solid white crystal that has the chemical formula H3PO4. However, it mainly occurs as an aqueous, non-volatile solution with an 85% concentration and a syrupy viscosity.
Phosphoric acid (also known as orthophosphoric acid and monophosphoric acid) is mainly used to manufacture phosphate fertilisers. About 90% of industrially-produced phosphoric acid is devoted to the fertiliser manufacturing sector. That being said, it’s also used to make other products such as food additives, soaps and detergents, toothpaste, and some pharmaceutical goods.
In addition, phosphoric acid is used as a precursor to many important phosphate salts, including:
- Sodium dihydrogen phosphate (NaH2PO4) – a salt that’s sometimes used as a chemical buffer to control the concentration of hydrogen ions or the acidity of solutions.
- Disodium hydrogen phosphate (Na2HPO4) – a phosphate integral to the large-scale treatment of municipal wastewater. It acts as a coagulant by removing highly-charged metal cations dissolved in water and allowing the minerals to precipitate at the bottom.
- Calcium dihydrogen phosphate (Ca[H2PO4]2 ) – also known as calcium superphosphate, this salt is a major ingredient in fertiliser products.
- Calcium monohydrogen phosphate (CaHPO4) – a compound that’s mainly used as a conditioning agent for salts and sugars.
Phosphoric acid in agriculture
Phosphoric acid has an important role in agriculture. It’s primarily used to manufacture phosphate fertilisers, although it can also help to manage soil pH and control pests.
Is phosphoric acid a good fertiliser?
Phosphoric acid isn’t normally used as a fertiliser on its own because it’s too corrosive. It could potentially kill important microorganisms and make the soil too acidic for plants to grow. Instead, the compound is used as a precursor for manufacturing other phosphate fertilisers.
The phosphorus in phosphates is used by plants to capture, store, and convert the energy of the sun into biomolecules, the most important of which is adenosine triphosphate (ATP). This biomolecule fuels important biochemical reactions, including photosynthesis. Adding phosphate fertilisers to crops can therefore boost plant growth, maximise crop production, and help farmers to meet food production targets.
Although phosphoric acid isn’t directly used as fertiliser, if the ground has rock or mineral phosphates, adding phosphoric acid will produce triple superphosphate, or TSP. This can then be absorbed by plants as a fertiliser.
Soil pH management
Various factors affect the pH of soil, such as climate and the type of soil. In the UK, most soils have a pH range of between 4.5 and 8.5. These are very acidic and too alkaline, respectively, for most garden plants and food crops to flourish.
Ideally, food crops grow in slightly alkaline soil with a pH range of 6.0 to 6.5. You can use phosphoric acid to lower the pH of soil if it becomes too alkaline.
Phosphoric acid in pest control
Phosphoric acid itself is not used as a pesticide but it is a precursor in the manufacture of organophosphates. These are designed to kill insects by disrupting their nervous systems, making them an effective insecticide and pest control agent. However, the use of certain types of organophosphates is now banned in the UK amid potential health concerns.
Phosphoric acid in the food industry
The economic viability of the food industry is dependent on the shelf life of the processed food and beverages it produces. In fact, the large-scale processing, storing, and selling of many food and beverage products is only possible because of preservatives like phosphoric acid.
Food-grade phosphoric acid is used in many food processing steps, mainly to control the pH. However, as we explain below, it can also act as a flavour enhancer and binding agent.
Preservation and shelf life
Food and beverages can quickly spoil if no effort is made to preserve them. Of course, it’s perfectly fine to skip this step if the food is meant to be consumed within a short while of being cooked. This is true for most of the fresh food that we cook on a daily basis.
However, processed food produced by factories needs to have an extended shelf life. In some cases, refrigeration is an option but it’s not always practical and won’t suit every type of food. Most food manufacturers therefore add preservatives like phosphoric acid to their products.
Phosphoric acid inhibits the growth of microorganisms like mould and bacteria, which can cause food to spoil and become inedible. It also helps to stabilise the texture of processed meat products.
Phosphoric acid used in flavour enhancing
Phosphoric acid is classified as a weak acid, which means it does not completely dissociate into hydronium and conjugate base ions when dissolved in water. The compound can therefore be added to food to improve its taste without drastically changing its chemistry.
For example, phosphoric acid is commonly added to cola flavoured fizzy drinks to give them their distinctive tart and tangy taste. At the same time, it helps to prolong the shelf life by preventing the growth of bacteria and mould.
Used as a binding agent
Phosphoric acid is often used as a binding agent for processed meats such as ham and sausages. It helps them to retain their water content and hold their shape. It also ensures they have a good texture, flavour, and colour.
Potential health and environmental concerns
Although phosphoric acid is used as a food additive, chronic exposure to the substance can cause some health problems. Inhaling phosphoric acid over the long term may lead to bronchitis with a cough, which is often accompanied by phlegm and breathing difficulties.
You’re also at risk of developing dermatitis if your skin is exposed to phosphoric acid over a prolonged period. The risks are greater if you suffer from chronic pulmonary disease or chronic skin disease, as phosphoric acid can exacerbate these conditions. Highly concentrated phosphoric acid can even burn the skin, so it’s important to wear PPE and take the necessary safety precautions.
But it’s not just the health implications we need to consider; there are also valid environmental concerns. For starters, phosphoric acid is potentially toxic to aquatic life. If a large quantity enters a water system, it can lower the pH and harm the organisms that live there.
Sustainable use of phosphoric acid
The mass production of phosphoric acid, whether through the wet or the dry process, produces some waste products and consumes a lot of energy. As a result, it can have a negative impact on the environment. The good news is sustainable mass production of the acid is possible through state-of-the-art equipment, such as that used by the team here at ReAgent.
We take our environmental obligations very seriously and have robust systems and processes in place to ensure we minimise our business’s impact on the environment. Read our environmental policy here or get in touch to find out more.
Conclusion
Phosphoric acid is important to both the agricultural sector and the food processing industry. It’s mainly used to manufacture phosphate fertilisers, but it also serves as a food additive and flavour enhancer. Although phosphoric acid isn’t toxic at low levels, it may have some negative health effects over the long term. There are also some environmental risks, although these can be managed by following responsible practices.
You can buy high-quality laboratory-grade or even food-grade phosphoric acid from our online shop here.
