I have been collecting used kitchen sponges from short term apartments for the last 5 years. It is a pity that this kind of material ends up in the rubbish. When you wash your dishes with a sponge, it sheds tiny fibers. These fibers, a type of microplastics, can’t be filtered out by water treatment plants. These end up in the ocean where they join the millions of metric tons of plastic dumped there every year. Τhe synthetic materials that they’re composed of continue to release dioxins and formaldehyde into soil and the atmosphere. Every sponge has its unique color from its use by different people that stayed in each apartment. I did a part of Oia in Santorini. One of the most visited place in Greece. If you have been to the island you know they have a problem with waste management.