Question: Why is it so important to use phosphate free soaps? Is there a difference in how they work? They don't seem much more expensive, but is there a catch? Also, why aren't all soaps phosphate free? We know it is possible since there are many on the market, and we are told that they are better for nature. So why still make the more harmful soaps?
Response: Phosphorus, generally in the form of phosphates, has historically been one of the main ingredients in detergents (which are soaps made from synthetic materials). In the detergents, phosphates served as a "builder" to improve the detergent's cleaning efficiency. Builders, such as STPP, are important to the cleaning process, as they help to remove dirt from the clothes and to minimize soap scum (often seen as a ring on the tub, washing machine, or shirt collars). The need for builders in detergents and soaps is especially important in areas with "hard" water that contain calcium and magnesium ions, since the builders prevent these ions from interfering with the cleaning process.
Of the detergent builders, phosphates were the most popular, because of their superior cleaning performance. Their strong cleaning performance, however, has increasingly been overshadowed by their harmful effects on rivers, lakes, streams, and other fresh waters. Levels of phosphates in these fresh water bodies can be much higher than normal as the result of contamination from municipal and domestic wastewater that contains phosphates -- some or much of which (depending on your perspective) comes from phosphate-containing detergents that go down the drain after use. Although phosphates are an important plant nutrient, higher than normal phosphate levels can destroy the health of the lake, stream or other fresh water body, as they allow algae in the water to grow faster than would naturally occur, turning clear lakes and rivers green and cloudy. This extra algal growth is not only unappealing to look at, but can also make the water smell bad and make it unsuitable for swimming. It can also make drinking water more expensive to filter and can spoil the taste or smell of the drinking water. In the long run, the excess algal growth can have devastating impacts on the health and age of a fresh water lake or river, causing eutrophication to speed up, where lakes and other water bodies fill in with dead algae and other organic matter and eventually turn into dry land.