is the chemical breakdown of materials, such as petroleum
products, by living organisms in the environment. The process depends on
certain microorganisms, such as bacteria, yeast, and fungi, which break down
molecules for sustenance. Certain chemical structures are more susceptible
to microbial breakdown than others; vegetable oils, for example, will
biodegrade more rapidly than petroleum oils. Most petroleum products
typically will completely biodegrade in the environment within two months to
two years.