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Projects: Pollution

 

The Clean Water Act defines "pollution" as the "man-made or man-induced alteration of the chemical, physical, biological, or radiological integrity of water."  More general pollution includes any alteration in the character or quality of the environment, or any of its components, that renders it harmful or less suited for certain uses.

Pollution can be classified according to sources:

 

Sources of Pollution:

Point Source Pollution: Comes from an identifiable source such as an industrial discharge pipe, an underground storage tank, sewage treatment plants or even agricultural feed lots and manure storage areas.

Nonpoint Source Pollution: Contamination does not originate from one specific location, and it often discharges over a wide land area. For example, as rain water flows across lawns, farms, streets, parking lots and other surfaces, it carries salt, pesticides, fertilizers, oil, grease, and many other pollutants to nearby waterways.  The source of any one pollutant cannot be identified.

 

There are numerous kinds of pollution. Below are 5 major categories of pollutants:

Pathogenic Organisms

Disease-causing organisms are found in human intestines, and therefore in human wastes.  These organisms cause a variety of diseases, and can be contracted when people drink water containing a sufficient number of these pathogens to cause infection.  Since the disease- causing organisms are difficult to measure in the laboratory, non-pathogenic bacteria - which can be easily detected- are measured to determine the quality of the water.  These bacteria are called fecal coliforms.  Fecal coliforms are harmless inhabitants of the human intestine - and are present in great abundance when waters have been contaminated with sewage.  When high levels of fecal coliforms are detected, there is a high probability that pathogenic organisms are also present.

Oxygen Demanding Substances

Oxygen is required by most living things, including organisms that live in water such as fish, insects, microscopic animals, and bacteria.  Oxygen is also needed for the decay of organic matter.  (Decay is the process in which bacteria and microscopic animals break down and consume organic material such as flesh, leaves, or fecal matter.) The amount of oxygen needed for the decay process is call the biochemical oxygen demand, or BOD.  When given as a concentration, such as parts per million, it is a measure of the oxygen needed in a given volume of water for the decay process to occur. When large amounts of organic waste material enter surface waters, bacteria multiply and decay can occur at a rapid rate.  This can deplete the oxygen in the surrounding water to levels below that which is needed by living organisms.  Organic wastes can come from human and animal sewage, agricultural practices, food processing, wood and paper mills, and numerous other sources.

Nutrients

All living organisms require nutrients for growth.  However, when nutrients are present in abundance in surface waters, nuisance or excessive growth of aquatic organisms, such as algae, can occur.  When the excess vegetation decays, it uses and removes the dissolved oxygen from the water being decomposed by bacteria, resulting in high levels of BOD (biochemical oxygen demand). The nutrients of greatest concern are phosphorus and nitrogen. Both are naturally present in surface waters and both are present in abundance in wastewaters.  Of the two - phosphorus is naturally in the shortest supply.  When additional phosphorus is available, the growth rates of vegetation increases significantly.  This can produce nuisance growths of algae and can cause changes in the species composition of aquatic plant and animal communities.  It can also accelerate eutrophication processes.  Eutrophication is generally associated with increasing plant growth and the slow filling of lakes with sediment and organic materials.  Nitrogen often occurs in the form of ammonia. It is a common constituent of sewage because it is a byproduct of the decay of organic material.  While ammonia is a nutrient that can be used by vegetation, since it is not the nutrient in shortest supply, it has limited detrimental effects.

Suspended Solids

Suspended solids are particulate material suspended in water, making it cloudy or turbid.  The matter can be composed of sediment particles such as clay or sand, or organic material such as decaying plant or animal matter.  Matter such as organic material, phosphorus, heavy metals and some toxic substances tend to adhere to suspended solids.  Suspended solids have various adverse effects on water. Some heavy metals, notably lead and most of the carbon-based toxic substances such as pesticides and polychlorinated biphenyls (PCB's) tend to adhere strongly to sediment particles in water.  In this way, they can be easily transported from one site to another. They can also be removed from the water column by settling.

Toxic Substances

These materials include heavy metals and organic chemicals used in manufacturing and agricultural practices.  When present in water - even in very small amounts - these materials can produce a variety of serious human and environmental problems.  Furthermore, many toxic substances do not break down or decay quickly in the environment.  There are currently 17 toxic metals of particular environmental concern:

Toxic Metals