Phosphate

What are phosphates and what properties do they have?

When talking about phosphates, we most often mean orthophosphates, i.e. derivatives of phosphoric acid (V) with  the chemical formula H₃PO₄.  Three hydrogen  atoms  can be replaced  by metal  cations  or ammonium ion (salts are formed)  or by organic  groups  (then esters are formed).  Phosphoric  acid can be dehydrated, resulting in:

• Pyrophosphoric acid H4P2O7 (its derivatives are pyrophosphates);
• Metaphosphoric acids (HPO3)ₙ, which form cyclic or linear polymeric acids (metaphosphates or polyphosphates);

• Polyphosphoric acids Hₙ+2PₙO3ₙ+1 (polyphosphates).

However, it is worth adding that phosphorus also forms other acids, in which it differs in the degree  of oxidation – trioxophosphoric acid (III) H₃PO₃ (phosphonic) and hypophosphorous acid (I) H₃PO₂ (phosphinic). They also find application in industry, but to a much lesser extent than orthophosphates.

Due to the diverse structure, phosphates have different physicochemical properties, which are used in specific branches of industry. The widest application is found by phosphates with chelating  abilities (binding  of metal ions), buffering abilities (pH stabilization), emulsifying abilities, as well as those which are hygroscopic and thermally stable (resistant to high temperature).

Application of phosphates in the food industry

Phosphates are very common  food additives, which mainly serve as acidity regulators, stabilizers, emulsifiers, antioxidants, preservatives, and leavening and anti-caking agents. On labels, they should be looked for under the designations E338 to E452. The series begins with phosphoric acid (E338), and then sodium phosphates, potassium phosphates, calcium phosphates, diphosphates, triphosphates and polyphosphates. They can be found, for example, as the main ingredient in carbonated beverages.

Phosphates in agriculture – a key component of fertilizers

In agriculture, phosphates are found in artificial fertilizers as a source of easily assimilable phosphorus, one of the three basic nutrients (along with nitrogen and potassium). Phosphorus is essential for the development of roots and the formation of flowers and fruits. The plant uses it in all metabolic processes – it is a component of ATP, the basic energy carrier.

In fertilizers, the content of this element is converted into the amount of P₂O₅. The most important types of phosphate fertilizers are (P₂O₅ content in parentheses):

• Single superphosphate (16-20%),
• Enriched superphosphate (40-50%),
• Ammonium phosphate, DAP (46%) – also provides nitrogen, which is why it is a very efficient fertilizer,
• Monoammonium phosphate, MAP (50-55%),
• Thermophosphates.

The role of phosphates in industrial chemicals

Phosphates  are also widely used in industrial  chemicals. They are added to plastics, textiles and industrial  materials as flame retardants, additives to paints and enamels, plasticizers,  thermal stabilizers  and water  treatment agents  (sequestrants  and scale inhibitors).

The impact of phosphates on the environment – challenges and regulations

The biggest challenge related to the use of phosphates is their impact on the environment, especially water. Overuse of these compounds leads to eutrophication of water,  i.e. excessive bloom of algae and cyanobacteria,  and consequently – oxygen deficit and death of aquatic organisms.  The main source of phosphates  is agriculture as well as municipal

and industrial wastewater, which is why EU regulations rather strictly regulate their use.

Alternatives to phosphates – are they possible?

Of course, there are alternatives to phosphates  that are used in the food industry (e.g. citrates, bicarbonates),  detergents (e.g. zeolites, polycarboxylates) or agriculture (organic fertilizers, recycled fertilizers or struvite).  Although they are biodegradable and support a closed-loop economy, their main drawbacks include  inter alia lower efficiency, higher costs or limited availability.

Standards and regulations regarding the use of phosphates

The use of phosphates  as food additives is strictly regulated by EU law. The most important legal acts are Regulation (EC) 1333/2008 and Commission  Regulations (EU) amending its annexes (No.1129/2011, 2017/871 and 2018/74). These regulations are intended to ensure that the consumption of phosphates by consumers does not exceed 70 mg/kg bw (expressed as phosphorus) – in accordance with the recommendation of the Scientific Committee on Food.

The standards  for the content  of phosphorus in detergents and cleaning agents are specified in Regulation (EU) No 259/2012 of the European Parliament and of the Council. They amount  to 0.5% of phosphorus in laundry  detergents and 0.3 g of phosphorus in a standard  dose of dishwasher detergents. As for artificial fertilizers, Regulation (EU) 2019/1009 of the European Parliament and of the Council does not specify the maximum content of phosphorus, but mainly addresses the issue of contaminants (e.g. cadmium) and promotes the use of organic and recycled fertilizers.