Although banana peels are commonly known for causing cartoon characters to slip, they actually have a much more important role in our lives: protecting us from pollutants that may slip into our water. Past research has shown that coconut fibers, peanut shells and other plant materials could potentially remove toxic heavy metals such as lead and copper from water. Current methods for purifying water of heavy metals are expensive and at times poisonous, therefore leading researchers to find alternatives to the current water purifiers.
Scientists at Sao Paulo State University in Brazil and their colleagues wanted to see if banana peels could act as water purifiers. The idea came about while researcher Gustavo Castro was eating some bananas at home. “I was at home eating some bananas when I had the idea, ‘Why not make something with this?’” The idea then grew as the research team began to observe the compounds in banana peels, finding significant results.
Compounds in banana peels contain nitrogen, sulfur and organic compounds such as carboxylic acids. These acids have their negatively charged electron pairs exposed, meaning they can bind with metals in the water that “usually have a positive charge,” Castro explained. Being able to bind with metals in the water allows the minced banana peel to perform as well or better at removing copper and lead than many other filtering materials, quickly removing both from water in the Parana River in Brazil. Besides being able to perform better than many other filtering materials, banana peels can also be used multiple times without losing their “metal-snagging properties.”
A purifier made of layers of minced banana peel could be used up to 11 times without losing its ability to grab the metals in water, and its natural material makes it dramatically cheaper and does not require a lot of work, unlike synthetic materials. Although this new development offers a new source of hope in developing countries, where water quality is low and water-screening technology is hard to come by, researchers say that no one should rush out to put mushed bananas into dirty water to make it potable.
“All these materials are produced in the laboratory with the same objective – to remove metals from water,” says Castro. Therefore, it is not as simple as grabbing mushed bananas and combining them with dirty water; it is much more than that. Castro and other researchers hope that this technique will someday be used in industrial settings as a cheap and non-toxic helper in the effort to ensure cleaner drinking supplies. The technique worked even at high levels of pH, which supports the idea of the technique being used in waste flows from industrial sources. Other types of “green” alternatives have been used such as sugar cane, coconut fibers and apple peels, but banana peels had never been used.
Castro and his colleagues were the first to use banana peels; starting off with flasks of water that contained pre-determined levels of positively charged copper and lead ions, they added dried and ground banana peels. After a few minutes there was less metal in the water than there was at the beginning of the experiment, showing that the peels had bound the metals. Although banana peels cannot actually be used to remove metals from water, their value lies in their ability to gather together trace amounts of copper and lead and make the metals easier to detect.
In the new study, banana peels increased the concentration of both metals by a factor of 20, making them very easy to sense, even with basic tools. “This is something that is interesting for people who have limited access to highly sophisticated instrumentation. They could use this as a pre-concentrator so that they could then detect minute quantities of metal, even with equipment that has high detection limits,” says Ashok Gadgil, an environmental engineer at the University of California, Berkeley. Gadgil agrees that banana peels do have some benefit in water monitoring, but believes that more research should be done on a wider range of banana types at different levels of ripeness. “I would want to know if a banana in Bangladesh works the same way as a banana in Brazil,” he says.