A River Soap Opera

Gone are the days when we had water in our rivers. Now we have something else- foam and froth!

And if you happen to pass by the Yamuna river in Delhi, you will notice a white layer floating on its surface. At first glance, this white blanket looks fluffy and ready to play with— like the water bubbles we have fun playing with. But it is barely so. So, what is froth and what's the science behind it? To know about this, we will have to peep into our houses and look at the different kinds of soap we use every day.

We use shampoos for our hair, detergents for clothes, dish-washing liquid /soap bars for utensils, bathing soap, liquid body wash, toilet cleaners, floor cleaners, recently introduced liquid hand wash…the list is endless.

How soaps/detergents works?

Water molecules prefer their own company, so they tend to stick together in drops. We call it surface tension. To make water wash better, we have to reduce its surface tension. The surfactants, that is, the surface active agents in detergents do the job.

A surfactant molecule has two ends. One end is attracted to water, while the other is attracted to dirt and grease. So the surfactant molecules help water to get a hold of grease, break it up, and wash it away.

We dump waste water from our homes to nearby water bodies. When air mixes with this water, foam is created.

But this is just the first half of soap opera. The water we receive is hard water, that is, water with a lot of minerals dissloved in it. Hard water is not good for washing as the dissolved minerals increase the surface tension of water. To get rid of this problem, the detergent industry adds more and more phosphorus or phosphate.

Now the real story begins. Thanks to the absence of a clear standard on phosphorus content in detergents, and a mad rush to make their product efficient, detergent makers end up adding up to 40-50 per cent of phosphate in their products when current USA standards limit the same at 2.2 per cent. In fact in Spain, the phosphate limit is even lower at 0.5 per cent!

The excess phosphate acts as a nutrient for algae and plants like water hyacinth, which see an unhealthy bloom. These then spread rapidly, leading to less sunlight and oxygen for other aquatic animals, including fish.