Understanding Biodegradation

• A plastic cup will not biodegrade.Jupiterimages/BananaStock/Getty Images
  
  To biodegrade is the same as to decompose. This means how the environment reduces an object back to its simplest elements by natural forces. Suppose you bury a slice of apple, a block of wood and a plastic cup side by side. If you dig the area up again in a year, the apple slice will be completely decomposed and the wood block will be partially decomposed, but the plastic cup will be unaffected. This illustrates the problem with plastics: they simply do not biodegrade. Nonbiodegradable substances have to eventually go somewhere, so they end up either in a landfill, recycled or as trash in the environment.
  
  

Persistance and Biodegradation Relationship

• A car biodegrades slowly, so its persistance is long.Hemera Technologies/AbleStock.com/Getty Images
  
  Persistence and biodegradation are opposing forces. The faster an object biodegrades, the weaker its persistence. Conversely, the stronger the persistence, the longer it takes to biodegrade completely. Suppose you bury a car fender and an apple side by side. If you come back in a year, the apple will be gone, and the car fender will be rusted but still there. Rust is iron ore, or iron in its pure form out of the ground. The apple biodegrades rapidly, so its persistence is low. The fender may take years to biodegrade back to iron ore, so its persistence is high.
  
  

Organic vs. Inorganic

• Another factor that determines persistence is if it's organic or inorganic. Organic means it came from the earth. Inorganic means that humans combined natural elements to form a substance that did not come from the earth. For example, glass is organic, being made out of molten sand. If you throw a glass bottle into a fast-moving river, then you are polluting. However, the bottle bashing on the rocks will break it apart. Over hundreds of years, the glass will be eventually ground back to sand. Its persistence is high, but not indefinite. If you throw a plastic toy into the river, then it will last for thousands of years, because plastic is not a natural substance. Plastic is made by recombining petroleum molecules into a different form, eventually becoming inorganic.
  
  

Study on Environmental Persistence

• Researchers Edward Little and Robin Calffee conducted a study for the United States Geological Survey regarding the effects of fire-retardant chemicals on the mortality rate of minnows. They discovered that different chemicals had different persistence rates. Some chemicals persist more than others. Furthermore, they used different river materials to apply the chemicals on, such as sand and gravel. They discovered persistence rates are also dependent on what the chemical is laying on. This research is significant, proving that persistence rates among one group of chemicals varies greatly both with the type of chemical and with the type of environment.