Non-Point Source

Non-point sources refer to numerous, relatively small sources of gases, metals, pesticides, nutrients, or other pollutants into the environment. Collectively, these many sources can represent a substantial contribution of pollutants into environment on a regional scale. Non-point sources are in contrast to point sources, which refer to discrete sources of pollution, such as a large smokestack or a sewage outfall.

For example, if the many buildings in a city are heated from electricity that is generated at a power plant that burns coal or oil, then it represents a point source of emissions of sulfur dioxide, oxides of nitrogen, and particulates to the atmosphere. The urban air quality will also be influenced by numerous other relatively small sources of emissions, for example, those from automobiles, trucks, and buses. Emissions from these non-point sources coalesce to contribute to regional air pollution.

In many coastal areas, sewage treatment facilities release treated waste into the ocean. This point source of pollution may include nitrogen, phosphorus, heavy metals and other complex chemical compounds. Non-point sources of pollution include runoff from yards and roads and the input from sewer systems during storms. Both of these sources contribute to water pollution.

Environmental degradation is caused by a combination of emissions of pollutants from both point–sources and non-point sources. Point sources are easier to identify and monitor. Extensive systems are in place to monitor the emissions from electrical facilitie, water treatment facilities and other large sources of pollution. Non-point sources on the other had are much more difficult to identify, much less regulate. Many environmental agencies have been able to put good controls in place for point source polluters, but have been unable to effectively solve the problem of pollution by non-point sources.

See also Point source.