In biodegradable, with its root grad, "to step or move", and its prefix de- "downward", we get an adjective describing things that can be broken down into basic substances through normal environmental processes. Animal and plant products are normally biodegradable, but mineral substances such as metals, glass, and plastics usually are not. Newly developed biodegradable plastics are now appearing in numerous products. However, "biodegradable" products can vary greatly in how long they take to break down. A loaf of bread may require only a couple of weeks, and a piece of paper may vanish in a couple of months, but some "biodegradable" plastic milk cartons may take four or five years.