Melamine sponges shed trillions of microplastic fibres every month, posing an environmental risk. Making denser sponges and using alternative cleaning methods are the recommended solutions.
Anyone who has ever worn white shoes or tried to scrub a crayon stain off a wall will be grateful for the melamine sponge. This sponge is known for its ability to easily remove stubborn stains and scratches without the use of detergents, thanks to its unique abrasive properties. But this “magic” sponge also sheds microplastic fibers as it wears down. According to a study published in ACS, Environmental Science and TechnologyIt is estimated that melamine sponges contribute to the release of more than 1 trillion microplastic fibres each month worldwide.
Melamine foam is made of poly(melamine-formaldehyde) polymers: a network of stiff plastic threads assembled into a soft, lightweight foam that’s surprisingly abrasive — the perfect material for a highly scrubbing sponge. But as the sponge wears down with use, the foam breaks down into tiny pieces, releasing microplastic fibers that can wash into sewer systems. Once released into the environment, the fibers can be ingested by wildlife and enter the food chain. Yu Su, Baoshan Xing, Rong Ji and colleagues wanted to see how the density of the melamine sponge and the roughness of the surface it’s scrubbing against affect how quickly the foam breaks down, and to calculate how many microplastic fibers might come off the sponge.
Research findings on microplastic emissions
The research team purchased several sponges from three popular brands and repeatedly rubbed them against an uneven metal surface to wear down the foam. They found that sponges made with denser foam wore down slower and produced fewer microplastic fibers than sponges with a lower density. The team then found that each sponge released about 6.5 million fibers per gram of worn sponge, and assumed that all sponges sold were worn down by 10% on average. To get a rough idea of how many fibers were released per month, they looked at Amazon’s monthly sales in August 2023. Assuming these figures were constant, the team calculated that melamine sponges could release 1.55 trillion fibers each month. However, this figure only considered one online retailer, so the actual amount may be higher.
To minimize the release of microplastic fibres, the researchers recommend that manufacturers produce sponges that are denser and more durable and more resistant to wear, and that consumers choose plastic-free and natural cleaning products, as well as install filtration systems in their homes or wastewater treatment plants to capture shed microplastic fibres.
Reference: Yu Su, Chenqi Yang, Songfeng Wang, Huimin Li, Yiyu Wu, Baoshan Xing, Rong Ji, “Mechanochemical formation of poly(melamine-formaldehyde) microplastic fibers during abrasion of cleaning sponges,” June 6, 2024;Environmental Science and Technology.
DOI: 10.1021/acs.est.4c00846
The authors gratefully acknowledge funding from the National Natural Science Foundation of China and the Guangdong Provincial Key Areas Research and Development Plan.