Sponges are very handy for work around the kitchen and the bathrooms, but they can be a serious problem. They have been found to collect and nurture more bacteria than you would find anywhere else in your home. As a result of this research, people began to purchase more sponges and then simply threw them away when they began to smell.
No consideration was paid to the environment at all. If you replace your kitchen sponge once a week, and multiply that by the number of households in this country alone, you are creating a serious addition to the landfill and are depleting our natural resources. Most sponges are made from plastic, which is derived from oil.
But there is more to it than that. To help eliminate the bacterial problem, they have now added Triclosan (a chemical pesticide that fights fungi and bacteria) to many sponges. This chemical has been linked to health problems, and is believed to destroy fragile aquatic eco systems. Since water treatment plants cannot remove it, it is now being found in our streams. Don't buy antibacterial sponges!
Cellulose sponges are your best bet, since they are recyclable. Make sure they do not contain polyester. Wash them, with bleach, regularly, by hand, in with your whites, or even in your dishwasher. Or boil them for a few minutes in plain water.
You can even grow your own sponge. Plant a Luffa plant in the garden, the fruit, when ripened and dried, becomes the loofah sponge you'd buy for your bubble bath!