Pollution is the release of environmental contaminants. The U.S., Russia, Mexico, China and Japan are the world leaders in air pollution emissions; however, Canada is the number two country on a per capita basis. The major forms of pollution include: * air pollution, the release of chemicals and particulates into the atmosphere. Common examples include carbon monoxide, sulfur dioxide, chlorofluorocarbons (CFCs), and nitrogen oxides produced by industry and motor vehicles. Ozone and smog are created as nitrogen oxides and hydrocarbons react to sunlight. * water pollution via surface runoff and leaching to groundwater. * Soil contamination occurs when chemicals are released by spill or underground storage tank leakage. Among the most significant soil contaminants are hydrocarbons, heavy metals, MTBE, herbicides, pesticides and chlorinated hydrocarbons. * radioactive contamination, added in the wake of 20th-century discoveries in atomic physics. (See alpha emitters and actinides in the environment.-------------------------------------Radioactive contamination is the uncontrolled distribution of radioactive material in a given environment.Radioactive contamination is typically the result of a loss of control of radioactive materials during the production or use of radioisotopes. For example, if a radioisotope used in medical imaging is accidentally spilled, the material could be spread by people as they walk around. Radioactive contamination may also be an inevitable result of certain processes, such as the release of radioactive xenon in nuclear fuel reprocessing. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations. Nuclear fallout is the distribution of radioactive contamination by a nuclear explosion. For a discussion of environmental contamination by alpha emitters please see Actinides in the environment. -------------------------------------------------------- Containment is what differentiates radioactive material from radioactive contamination. Therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same.-----------------------Toxic waste is waste material, often in chemical form, that can cause death or injury to living creatures. It usually is the product of industry or commerce, but comes also from residential use, agriculture, the military, medical facilities, radioactive sources, and light industry, such as dry cleaning establishments. As with many pollution problems, toxic waste began to be a significant issue during the industrial revolution. The term is often used interchangeably with “hazardous waste,” or discarded material that can pose a long-term risk to health or environment. Toxics can be released into air, water, or land.