3.1 Phosphates in the environment
Most detergents or surfactants, comprise long molecules with hydrophobic (water-repelling) and hydrophilic (water-attracting) parts as indicated in the example in Structure 6. The basic action is for the organic hydrophobic section to bury itself in the dirt, and the hydrophilic section then allows the insoluble dirt to 'dissolve' in water.
Detergents are used in combination with so-called builders, which soften hard water. Hard water contains significant concentrations of calcium and magnesium salts, which replace the sodium ions in the detergent molecule. The dipositive metal ions cause the long detergent molecules to clump together and precipitate out as a scum.
Sodium tripolyphosphate (Structure 7 see also Section 3.2.1), was used in detergents to complex magnesium and calcium ions and hence remove them from solution. Due to environmental concerns over such polyphosphates acting as nutrients for algae (leading to eutrophication), detergent manufacturers have phased out the use of so-called phosphate builders. Substitute detergent builders include zeolites, such as ZSM-5 NanAlnSi96−nO192·16H2O (0 < n < 27), which are porous, non-eutrophic materials that exchange sodium ions for calcium ions and hence soften water.
