Does biodegradable mean environmentally healthy?

"Biodegradation" is defined as "the destruction of organic compounds by micro-organisms." A biodegradable object&a leaf, for example&is broken down by bacteria in soil or water into its component elements: carbon dioxide, water, and minerals.

But what if the object isn't natural but rather made of a synthetic substance such as a petroleum-based plastic? While crude oil itself will eventually biodegrade, plastics don't because no micro-organisms exist that can consume and break them down.

The plastics industry, however, is developing plastics that are degradable (plastics that break down under certain conditions but leave waste products that are not digestible by micro-organisms), biodegradable (plastics that micro-organisms can eventually break down), and compostable (plastics that biodegrade in a manner similar to natural compostable materials such as garden waste).

The issue of whether biodegradable substances are always environmentally friendly is further complicated when we talk about quantities and conditions. Soap, which may biodegrade in small quantities in fresh, running water, will not easily do so when disposed of in massive quantities. Newspaper, when exposed to soil bacteria, water, and air, ordinarily biodegrades within two to five months, but when buried in landfills may still be in readable condition 25 years later.