Air pollution is the 5th highest death risk, among factors such as smoking, diet and high blood pressure. Here are the most deadly countries for air pollution.

Air pollution can have both man-made and natural sources. The Eyjafjallajokul volcano in Iceland and Mount St. Helen in Washington illustrate the effect of natural causes of air pollution. However, humans continue to negatively impact their environments and contribute to air pollution.

Pollution is a significant problem facing the environment. As the world's population continues to grow, so does the amount of potentially toxic substances that are released into the ecosystem. Environmental pollutants can be derived from a number of sources.

Industrial pollution is one of the primary sources of environmental contamination. According to the U.S. Environmental Protection Agency (EPA), air pollution levels rose 14 percent from 1990 to 2008. This trend reflects the amount of human-caused greenhouse gas emissions in the air.

Items that break down over time naturally, like food scraps or paper, are biodegradable. According to the World Wildlife Foundation, most biodegradable items are made from animals or plants, but some artificial materials designed to mimic these organic substances can also degrade over time.