Natural Resource Damage Assessment (NRDA)

Natural Resource Damage Assessment is the legal and technical process to pursue restoration for damages to natural resources caused by discharges of oil and releases of hazardous materials into the environment. Federal and state agencies, and Native American tribal governments are designated as NRDA trustees.

Nelson, Gaylord U.S. Senator (D-Wisconsin) and Founder of Earth Day (1916–)

One of the first and most effective environmentalists elected to the U.S. Senate, Gaylord Nelson is considered the father of Earth Day and sponsored many of the important environmental laws passed by Congress in the 1960s and 1970s.

New Left

In the 1930s and through the 1950s, a political movement known later as the "Old Left" emerged in American politics. A liberal group of predominantly northern intellectuals, the Old Left shared a fascination with labor problems and frequently maintained an interest in communism as a solution to America's economic troubles.

NOx (Nitrogen Oxides)

NOx is a common term for the more reactive nitrogen oxides and includes nitric oxide (NO) and nitrogen dioxide (NO2), but excludes, for example, nitrous oxide (N2O). NO2 is a reddish brown, highly reactive gas that is formed in the air by the oxidation of NO.

Noise Control Act of 1972

In passing the Noise Control Act (NCA) of 1972, Congress hoped to "promote an environment for all Americans free from noise that jeopardizes health or welfare." The Office of Noise Abatement and Control (ONAC) of the Environmental Protection Agency (EPA) was charged with overseeing noise-abatement activities and coordinating its programs with those of other federal agencies that play an important role in noise control. The Noise Control Act was amended by the Quiet Communities Act of 1978 to promote the development of effective state and local noise control programs, to provide funds for noise research, and to produce and disseminate educational materials to the public on the harmful effects of noise and ways to effectively control it.

Noise Pollution

Noise pollution is the intrusion of unwanted, uncontrollable, and unpredictable sounds, not necessarily loud, into the lives of individuals of reasonable sensitivities. Using the "reasonable person" standard removes the notion that the judgment of sounds as unwanted is subjective.

Nonaqueous Phase Liquids (NAPLS)

Nonaqueous Phase Liquids (NAPLs) are hazardous organic liquids such as dry cleaning fluids, fuel oil, and gasoline that do not dissolve in water. A significant portion of contaminated soil and groundwater sites contain NAPLs, and they are particularly hard to remove from the water supply.

Nongovernmental Organizations (NGOs)

Collaborative efforts among the public have played an important role in shaping the political and social values and hence public policy of the United States. Organizing with others who share a similar vision enhances the potential for change.

Nonpoint Source Pollution

Nonpoint source pollution occurs when rainfall or snowmelt runs over land or through the ground, picks up pollutants, and deposits them into rivers, lakes, wetlands, and coastal waters or introduces them into groundwater. Some of the primary activities that generate nonpoint source pollution include farming and grazing activities, timber harvesting, new development, construction, and recreational boating.

Nuclear Regulatory Commission (NRC)

The Nuclear Regulatory Commission's (NRC) primary mission is to protect public health and safety and to protect the environment from the effects of radiation from nuclear reactors, materials, and waste facilities. The NRC is empowered by the Atomic Energy Act of 1954 and its amendments to regulate source material (primarily uranium ore and processed uranium), special nuclear material, including material enriched in plutonium or the isotope uranium-235 above certain levels, and by-product material, and to regulate the uses of these materials.

Occupational Safety and Health Administration (OSHA)

The Occupational Safety and Health Administration (OSHA), the federal agency charged with protecting workers' health and safety, was created by Congress in 1971 to administer the Occupational Health and Safety Act of 1970. With few exceptions, including some state plans and specific industries, OSHA oversees all U.S.

Ocean Dumping

Ocean disposal of society's waste got its start indirectly long before the Agricultural Age when nearby streams, lakes, and estuaries were useful as waste repositories. As civilization moved to the coastal zone and navigation began in earnest, the oceans were viewed as even a larger waste repository.

Ocean Dumping Ban Act

The Ocean Dumping Ban Act, enacted in 1988, significantly amended portions of the Marine Protection, Research and Sanctuaries Act of 1972 and banned ocean dumping of municipal sewage sludge and industrial waste (with limited exceptions) by phased target dates. The disposal of sewage sludge in waters off New York City was a major motivation for its enactment.

Oxygen Demand, Biochemical

Biochemical oxygen demand (BOD) is a measure of how much organic pollution is in water. The BOD test measures the amount of dissolved oxygen in water that is used up due to the breakdown of organic pollutants, such as sewage, in a certain number of days.


Ozone is a gas found in the atmosphere in very trace amounts. Depending on where it is located, ozone can be beneficial ("good ozone") or detrimental ("bad ozone").


Particulates, or particulate matter (PM), refer to any mixture of solid particles or liquid droplets that remain suspended in the atmosphere for appreciable time periods. Examples of particulates are dust and salt particles, and water and sulphuric acid droplets.

PCBs (Polychlorinated Biphenyls)

PCBs, known to cause cancer in animals and believed to cause cancer in humans, are among the most widespread and hazardous synthetic pollutants. They comprise a group of 209 structurally similar compounds, so-called congeners.

Persistent Bioaccumulative and Toxic (PBT) Chemicals

Persistent bioaccumulative and toxic (PBT) chemicals represent a group of substances that are not easily degraded, accumulate in organisms, and exhibit an acute or chronic toxicity. They may therefore pose serious concerns for human and environmental health.

Persistent Organic Pollutants (POPs)

Persistent organic pollutants (POPs) are a subset of the more comprehensive term persistent bioaccumulative and toxic chemicals (PBTs). POPs commonly stands for organic (carbon-based) chemical compounds and mixtures that share four characteristics.


Fumigators walking down a street in the Sultan Mosque area of Singapore and spraying a pesticide to rid the area of mosquitoes. (©Steve Raymer/Corbis.


Petroleum is a naturally occurring liquid oil normally found in deposits beneath the surface of the earth. It is a type of oil composed of rock minerals, making it different from other kinds of oils that come from plants and animals (such as vegetable oil, animal fat, or essential oils).


Pure phosphorus is rare in nature. It usually combines with oxygen to form phosphate ions or groups (PO 3- 4 ).