The term biodegradable is used to describe substances that are capable of being broken down, or decomposed, by the action of bacteria, fungi, and other microorganisms. Temperature and sunlight may also play a role in the decomposition of biodegradable substances. When substances are not biodegradable, they remain in the environment for a long time, and, if toxic, may pollute the soil and water, causing harm to plants and animals that live in these environments. Humans can also be affected by drinking water or eating crops contaminated by these toxic substances.
Common, everyday substances that are biodegradable include food wastes, tree leaves, and grass clippings. Many communities now encourage people to compost these materials and use them as humus (decayed organic material in soil) for gardening. Because plant and animal materials are biodegradable, this is one way to for towns and cities to reduce solid waste.
The development of detergents in the 1950s and the problems their surfactants caused (wetting agents that allow water to dissolve greasy dirt) raised the issue of the biodegradability of these chemicals. It was found that bacteria in sewage systems degraded some surfactants very slowly. This resulted in the chemicals being released into lakes and streams not fully decomposed and forming suds in the water. Environmental concerns led to the development of new detergents that are more easily biodegradable.
In efforts to control the use of nonbiodegradable materials, governments and industries have taken various measures. For example, the plastic rings that bind six-packs of soda and beer pose a danger to wildlife, who can becoming entangled in them; these rings must now be biodegradable by law in Oregon and Alaska. Italy has banned all nonbiodegradable plastics. Certain manufacturers have responded to the issue by experimenting with biodegradable packaging of food. Many garbage bags and disposable diapers are now being made using degradable plastics, with the goal of reducing litter, pollution, and danger to wildlife.
[ See also Composting ; Recycling ; Waste management ]