Sapindus nuts for washing clothes: a substitute for detergents?

Flavia, member and reader of eldiario.es, writes us the following text in an email: "I am writing to you because recently an ecology blog that I follow, and where I buy some household products, put up for sale wash nuts from the Sapindus mukorossi tree , and promotes them as a green alternative to detergent.Before I bought it, I did some research on the subject, and the truth is that it is not at all clear to me that it is really an environmentally friendly alternative, since there is a study that shows that it does not solve the question of the consequences of saponin in the water, which is not harmless for fish and cold-blooded animals. Anyway, if at some point you can investigate about it and do an article, it would be great " .

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The Sapindus mukorossi tree comes from the regions of Nepal and the Himalayas, although there are also other species of the Sapindus genus in different areas of the planet's tropical climate belt. It is a tree used from ancient times for different purposes, both medicinal and ornamental and for cleaning. Among other properties, this tree is characterized by having shelled fruits similar to walnuts that have a high content of a surfactant known as saponin.

Saponins are a product present in many plants to which fungicide and perhaps bactericide purposes are attributed, and in general defense given its bitter taste. Precisely their ability to break surface tension allows them to act like a soap, since in the presence of water and heat they are capable of dissolving fats, which is why they are supposed to act against the bacterial and fungal cell wall.

In the same way, this quality of saponins has made them a good natural detergent since ancient times when synthetic soaps did not exist, and it is verified that both in the communities of the north of the Indian subcontinent and in tropical America, the berries of the different species of the Sapindaceae family have been used to wash clothes in the presence of hot water. Therefore, its effectiveness as a detergent is proven, and even a study by a young researcher at the University of Santiago in 2009 confirmed its effectiveness against commercial detergents.

How to use sapindus nuts

Sapindus nuts are commercially available from many online retailers, including portals such as Amazon. They present, among other advantages, the fact that they can be used in several uses, calculating that on average one kilo can be used for almost a year, always depending on the number of washes. As a reference, three walnut shells -which are the ones that contain saponin- are good for two washes at high temperature, twice as much if washed at 30ºC.

Its use is very simple: three nuts are cut and the shells are preserved, which will be placed in a cotton bag that will be placed next to the clothes in the washing machine drum. As we have already said, if it is washed between 60º and 90ºC, it can be used again, and if it is used at 30º it can be used up to four times. Now, if you want to use them cold, we must place the shells in boiling water and leave for five minutes over medium heat, and then allow the mixture to cool. We will thus obtain a liquid detergent that we will use in the same way as the commercial ones.

On the other hand, saponin can also have other uses as natural soap: for hands, hair, etc. However, if the clothes have stains that are resistant, we must add along with the shells of nine sodium precarbonate -sold in drugstores and perfumeries- that will release oxygen molecules on contact with water that will eliminate the most resistant dirt. Percarbonate, once it has reacted, is completely harmless and decomposes into carbonate and hydrogen peroxide.

Are they really an ecological alternative?

Unlike commercial detergents, saponin does not include phosphorus, an element that is used to treat calcium hardness in washing water and that passes into the aquatic environment. Although the detergent degrades, as most do so effectively, phosphorus as an element is difficult to control in water treatment plants and has the problem that it is a great nutrient for photosynthetic functions.

In this way, the addition of large amounts of phosphorus to the medium implies that there will be a large growth of algae thanks to phosphorus. And these algae will serve as food for zooplankton and other species in the environment, which in turn will feed fish and invertebrates, accelerating the food chain and consuming all the oxygen in the water. In the end, they will hypertrophy the ecosystem and lead to a lack of oxygen (anoixa) without giving it time to regenerate itself.

Faced with the problem of phosphorus, saponin has the advantage that it does not release micronutrients into the environment when it biodegrades, which it also does quickly. However, and as Flavia says, not all are advantages, at least if we put ourselves in a scenario of massive use of sapindus nuts. Saponins are highly toxic to many invertebrate, fish, and bivalve species. In fact, they are commonly used to fight in the Ebro Delta against invasive species of mollusks in rice fields, with good results as long as certain doses are not exceeded.

They are also used as a phytochemical and to clean shrimp farming ponds. Consequently, in a hypothetical massive use of sapindus nuts to wash clothes, the saponins could present serious problems for the environment, as long as the water treatment plants were not capable of neutralizing them or leading them to biodegradation, something that has not been proven. let them happen But as long as this scenario does not occur and in the hope that water treatment plants can eliminate huge amounts of saponin -which is unknown-, they are an interesting ecological alternative to commercial detergents.

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