A phosphate group contains the elements phosphorous and oxygen. The phosphorous atom is bonded to four oxygen atoms with three single bonds and one double bond. If one of the oxygen atoms is bonded to another atom, it is a phosphate group; without this bond, it is a phosphate ion.
Phosphate is an essential nutrient for plants and animals. Because it is necessary to so many organisms, it is often the limiting nutrient in freshwater ecosystems. A limiting nutrient is one that limits further growth due to its scarcity; when more of the limiting nutrient enters an ecosystem, all other factors allow for more growth. Phosphorous is not generally a limiting nutrient in saltwater ecosystems.
Because of its status as a limiting nutrient outside of marine environments, phosphate is a common fertilizer. Natural phosphate mined for fertilizer can be contaminated with heavy metals, such as cadmium, nickel, lead, chromium, copper and uranium. In addition to the risk of heavy-metal toxicity, uranium presents a radioactive contamination hazard. These metals contaminate food grown using contaminated phosphate, and can leak into the water supply.
Phosphate can also be used to produce phosphoric acid. This and chemical fertilizers are the two primary uses of phosphates in industry.