Nitrogen is a non-toxic inert gas that does not chemically react with other gases. However, inhaling pure nitrogen is lethal. This is due to the gas displaces oxygen in the lungs. Unconsciousness can develop within one or two breaths of each other, according to the United States Chemical Safety and Hazard Investigation Board. Nitrogen is used in medicine, food storage, and airships to prevent insects from breeding. Pure nitrogen is the most abundant element in the atmosphere. It makes up 78% of the air we breathe. Nitrogen is the main component of ammonia, which is used as a fertilizer and cleanses soil of toxic substances. Ammonia is also the main ingredient in household cleaning products such as Window Cleaner and Dishwashing Liquid. Natural sources of nitrogen are nitrates derived from decomposed plants and animals. Soils contain large quantities of nitrogen in a form that can be absorbed by plant roots. Fertilization practices including manure and biological agents (such as bacteria) help increase the amount of available nitrogen on farms. The largest source of nitrogen pollution comes from the manufacturing industry. The process of making explosives, pesticides, and fertilizers produces carbon dioxide and various chemicals that are harmful to the environment. In addition, the disposal of unused chemicals can lead to groundwater contamination. Nitrogen pollution can also come from road accidents that produce broken glass and plastic that contains nitrogen atoms.