Environmental Impacts of Soaps and Detergents

These products are designed to be used once and then flushed down the drain.
As such, they can have a varying range of impacts (possibly significant) upon the

  • Biodegradability:

The earliest developed synthetic detergents were non-biodegradable due to their
branched hydrocarbon chains. It was discovered that they did not decompose
within a few days and thus persisted in the environment. These caused
waterways in the 1960s and 70s to build up with foam. Industrial chemists
eventually rectified this problem by synthesising detergents with non-branching
tails. These are more easily broken down by microbial decomposers.
On the other hand, soaps are biodegradable as they are single-chain
hydrocarbons (derived from fatty acids). These are easily broken down within 5

  • Phosphate Builders:

Synthetic detergents were developed in part to combat the failure of soap to
work in hard water. The soap anion molecules form a grey scum precipitate with
Ca2+ and Mg2+, which persists on clothing. While detergents don’t form this
precipitate, the presence of these ions causes their effectiveness to be reduced.
As such, many detergents have added phosphate builders such as Na5P3O10 to
reduce water hardness and increase cleaning power. These builders form
complexes with the metal ions and ‘remove’ them from the water. However these
builders, with the detergent, can enter domestic sewage and end up in
waterways. Recall that phosphate is a nutrient for many organisms and
increased concentrations of it lead to eutrophication, algal blooms and
Thus, in many countries there are restrictions on the amount of phosphates
allowed in washing powders and liquids. Also, zeolites are now being used to
replace phosphate builders since they do not cause eutrophication. Phosphate
builders are not added to soap as they do not have an effect on body cleaning.

  • Biocidal Properties:

Cationic detergents have mild biocidal properties, as they disrupt the cellular
processes in bacterial cells. Thus, their presence in wastewater and sewerage
can cause the bacteria which breaks down waste to be killed. This occurs at
higher concentrations only; lower concentrations of cationic detergents don’t
harm the bacteria which break them down.