Cindy Leung, age 10, of San Francisco, California, for her question:

What does biodegradable mean?

This long word was built from several smaller words to describe how nature uses and reuses waste materials. Bio means living; degrade means to break down. In a biodegradable material, the chemical molecules can be broken into smaller molecules to enrich the soil and feed the plants that feed the animals. The living things that do this work are tiny bacteria that cause decay.

In nature, fallen leaves, animal wastes and even rusty metals are degraded and reused again and again. But some of our man made chemicals have larger, tougher molecules. For example, it takes ages for some of our detergents to break down into safe or usable chemicals. Meantime, they clog our waterways, harming fishes and other creatures. Many chemical weed and bug killers are not easily biodegradable. Some are poisons that birds and other animals consume with their food. These non¬biodegradable chemicals are polluting our land and seas and threatening the lives of countless living creatures