Context: In what has become a repeat occurrence in the city, a layer of froth was seen floating over parts of the Yamuna river near Kalindi Kunj, Delhi.
About Froth Formation

• This is a phenomenon that takes place on many lakes and streams.
• Foam bubbles are produced when organic matter decomposes.
• These foam-producing molecules have one end that repels water and another that attracts water and they work to reduce the surface tension on the surface of the water.
• These foam bubbles are lighter than water, so they float on the surface as a thin film that gradually accumulates.
• This lowers the oxygen content, killing off marine life that is essential to maintain the quality of water.
• These phosphates are responsible for the alarming amount of foam that forms on the surface of the river, similar to the foam created by detergents.

What causes the froth?

• The presence of phosphates and surfactants in untreated sewage from Delhi, Haryana and Uttar Pradesh is a major reason behind frothing.
• While these two components comprise of 1 per cent, the remaining 99 percent is air and water.

What are the sources of pollution that cause foam formation?

• Untreated sewage may contain soap-detergent particles.
• The other sources are industrial effluents, organic matter from decomposing vegetation, and the presence of filamentous bacteria.
• The pollution from the sugar and paper industries in Uttar Pradesh also causes pollution in the Yamuna.

Natural Causes

• Dead and decaying parts of plants contain fats molecules that do not mix with water.
• They form an invisible floating layer on the water surface.  When the water gets disturbed by waves, this fatty layer gets beaten into a froth.
• The foam made from organic matter in rivers and lakes can last for a long time.

Manmade Causes

• The high level of phosphates in the rivers is what causes such foam to build up.
• Phosphates are an ingredient used in many detergents which are designed to reduce the surface tension of water. These compounds make cleaning a lot easier.
• However, these phosphates persist in water, which leads to eutrophication.

Note: Eutrophication is a process by which a water body becomes enriched with minerals and nutrients, causing the growth of algae that in turn cuts off oxygen from mixing with the water and sunlight from reaching the depths of the water body.
What are its health hazards?

• Short-term exposure can lead to skin irritation and allergies.
• If ingested, these chemicals may cause gastrointestinal problems and diseases like typhoid.
• Long-term exposure to heavy metals in industrial pollutants can cause neurological issues and hormonal imbalances.