Phosphates are found in all animal and plant cells, in food, in cosmetic chemistry, detergents, medicines and fertilizers. They are used in many branches of industry – automotive, construction, petrochemical, textile, etc. But what are these chemical compounds? What properties do they have and are phosphates used exclusively orally?
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:
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).
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):
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 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.
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.
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.
