P is for phosphorus, an element which in its mineral form (as found in nature) is essential for life. In the form of phosphate, it has become one of the most widely applied "nutrients" on the farm. The problem is Irish soils have become overloaded with phosphorus, as elsewhere in developed countries.
Phosphate has a new reputation as a water pollutant, especially when the loadings from sewage and various detergents are factored in.
It enriches the water, making it vulnerable to pollution, depletes oxygen and upsets its natural balance.