this is what I found on phosphates....
Phosphate is a molecular anion that carries 3 extra electrons: PO43-.
In terms of naming rules, note that we use the ending -ate for this, the most common oxyanion
in the phosphorus oxyanion series. Phosphate also forms the base for a series of acidic compounds
formed by adding 1, 2, or 3 protons to the anion:
PO43- + H+ --> HPO42- hydrogen phosphate ion
PO43- + 2H+ --> H2PO4- dihydrogen phosphate ion
PO43- + 3H+ --> H3PO4 phosphoric acid
This set of compounds forms a buffer system commonly used in colas and other soft drinks.
Compounds containing phosphates are used as fertililizers because the P atom is an essential nutrient
for many organisms. It is used in detergents because the high charge of the phosphate ion gives it desirable
properties in changing solubility of "dirt". The chart below shows an input/output cycle of a freshwater pond
ecosystem. If too much phosphate gets in the water from agricultural runoff or from sewage treatment plants,
or industrial waste, the algal life cycle which was formerly limited or restrained by the limited phosphorus, takes off.
The result is a "bloom" of algae in the pond or lake which eventually depletes the oxygen dissolved in the water
and leads to massive fish kill and "dead" lakes. The dismal condition of Lake Erie in the 1960s was very much
due to this phenomenon. (From Chemistry of the Environment, Spiro & Stigliani, Prentice Hall, 1996)