Water Pollution
Contamination of water, typically by foreign matter such as microorganisms, chemicals, industrial or other wastes, or sewage. Pollution deteriorates the quality of the water, introducing toxic substances or organisms or otherwise altering the water's character, with potentially destructive consequences for living things and habitats.
The major pollutants of water are the following:
- Sewage and other oxygen-demanding wastes (largely organic material, the decomposition of which leads to oxygen depletion)
- Infectious or toxin-releasing agents, such as the parasites Giardia lamblia (which lodges in the intestine causing a diarrheal illness called giardiasis) and Cryptosporidium parvum (which causes cryptosporidiosis, also commonly characterized by diarrhea), as well as the dinoflagellate Pfiesteria and the bacterium Escherichia coli O157:H7.
- Plant nutrients, including chemical fertilizers, that can stimulate the growth of aquatic plants, which then interfere with water uses and, when decaying, deplete the dissolved oxygen and produce disagreeable odors
- Exotic organic chemicals, including pesticides, various industrial products, surface-active substances ("surfactants") in detergents, and the decomposition products of other organic compounds
- Petroleum, especially from oil spills
- Inorganic minerals and chemical compounds
- Sediments consisting of soil and mineral particles washed by storms and floodwater from croplands, unprotected soils, strip mines, roads, and bulldozed urban areas
- Radioactive substances from the wastes of uranium and thorium mining and refining, from nuclear power plants, and from the industrial, medical, and scientific use of radioactive materials
Heat can also be a habitat-disturbing pollutant. Such so-called thermal pollution can occur when increased temperatures in bodies of water result from the discharge of coolant water by factories and power plants. Other possible causes include soil erosion, loss of forest cover along shorelines, and runoff from hot paved surfaces.
Notable effects of water pollution include those involved in human health. Nitrates in drinking water can cause a disease in the red blood cells of infants, methemoglobinemia, that sometimes results in death. Cadmium in sludge-derived fertilizer can be absorbed by crops; if ingested in sufficient amounts, the metal can cause an acute diarrheal disorder and liver and kidney damage. The hazardous nature of mercury, arsenic, and lead has long been known or strongly suspected. In 2004 polluted water was linked to an estimated 3500-5500 cases of illness in the U.S., according to the country's Environmental Protection Agency (EPA). Major outbreaks, although rare in the U.S., are possible. In 1993 the Milwaukee, Wisc., area experienced a massive outbreak of cryptosporidiosis; about 400,000 people fell ill, and some 100 died. The causative parasite was transmitted through the public water supply.
Lakes are especially vulnerable to pollution. One problem, eutrophication, occurs when lake water becomes artificially enriched with nutrients, causing abnormal plant growth. Runoff of chemical fertilizer from cultivated fields may trigger this. The process of eutrophication (which also occurs in other types of bodies of water) can produce aesthetic problems such as bad tastes and odors and unsightly green scums of algae, as well as dense growth of rooted plants, oxygen depletion in the deeper waters and bottom sediments of lakes, reduced water clarity (potentially leading to death of bottom-dwelling plants), and chemical changes such as precipitation of calcium carbonate in hard waters. Another problem is acid rain, which has destroyed populations of entire species in some lakes in such regions as the northeastern U.S. and Canada.
Scientists distinguish two types of pollution sources: point and nonpoint. Point sources are localized and emit contaminants directly into a body of water, as in an oil spill from a ship. In cases where a localized source cannot be identified, the pollution is said to have a nonpoint source, as may happen when runoff carries agricultural fertilizer into a river. Point sources are generally much easier to monitor and control. Most of the pollutants in U.S. streams and lakes today derive from nonpoint sources.
Comprehensive data on water quality are lacking. In the U.S., the EPA's National Water Quality Inventory Report for 2000, based on limited information gathered for about a third of the country's waters, found that 39 percent of the river and stream miles that were assessed, 45 percent of the lake areas, and 51 percent of the estuaries were impaired for one or more desired uses, such as fishing or swimming. The major sources of water pollution varied from localized causes to diffuse ones. A common classification categorizes them as municipal, industrial, or agricultural.
Municipal water pollution consists of wastewater from homes and commercial establishments. For many years, the main goal of treating municipal wastewater was simply to reduce its content of suspended solids, oxygen-demanding materials, dissolved inorganic compounds (particularly compounds of phosphorus and nitrogen), and harmful bacteria. More recently, stress has also been placed on improving the means of disposal of the solid residues from municipal treatment processes. The basic treatment of municipal wastewater falls into three stages: primary treatment, including grit removal, screening, grinding, flocculation, and sedimentation; secondary treatment, which entails oxidation of dissolved organic matter, using biologically active sludge, which is then filtered off; and tertiary treatment, using advanced biological methods of nitrogen removal and chemical and physical methods such as granular filtration and activated carbon adsorption.
The characteristics of industrial wastewaters can differ markedly both within and among industries. The impact of industrial discharges depends not only on their collective characteristics, such as biochemical oxygen demand and the amount of suspended solids, but also on their content of specific inorganic and organic substances. Three options (which are not mutually exclusive) are available in controlling industrial wastewater: Control can take place at the point of generation within the plant; wastewater can be pretreated for discharge to municipal treatment systems; or wastewater can be treated completely at the plant and either reused or discharged directly into receiving waters.
Agriculture, including commercial livestock and poultry farming, is the source of many organic and inorganic pollutants in surface waters and groundwater. Aquaculture, whether carried out in ponds or holding tanks on land or in pens in seawater, can also be a cause of pollution. Agricultural contaminants include both sediment from the erosion of cropland and compounds of phosphorus and nitrogen that partly originate in animal wastes and commercial fertilizers. In addition to these materials, agriculture (and also aquaculture) may release into the environment such substances as pesticides, nutritional additives, hormones, and antibiotics and other pharmaceuticals. Since animal wastes tend to be high in oxygen-demanding material, nitrogen, and phosphorus, they often harbor pathogenic organisms. Wastes from commercial feeders are typically contained and disposed of on land; their main threat to natural waters, therefore, is via runoff and leaching. Control may involve settling basins for liquids, limited biological treatment in aerobic or anaerobic lagoons, and a variety of other methods. Among other antipollution measures, erosion control techniques are helpful in reducing nutrient pollution.
Most of the wastes discharged directly into U.S. marine waters are produced by dredging. Other notable pollutants include industrial waste, discharges from oil and gas drill rigs, and sewage sludge. Runoff containing nutrient materials, such as from fertilizers, is a problem particularly in coastal waters. A 2003 report by the Pew Oceans Commission, an arm of the nonprofit Pew Charitable Trusts, found that over 60 percent of U.S. coastal rivers and bays were moderately or severely degraded by nutrient runoff. Ships constitute another noteworthy cause of marine pollution, releasing into the ocean bilgewater, ballast water, and sewage and other wastes, along with unintentional spills of substances such as petroleum products. The atmosphere is also a significant source of contaminants for the ocean, as it is above the land, where acid rain can pollute streams and lakes. Atmospheric deposition is a key avenue for the entry of nitrogen, metals such as lead and mercury, and chemicals such as DDT and PCBs into coastal and ocean environments. The presence of toxic substances, the rapid uptake of contaminants by marine organisms, heavy deposits of materials on the bottom environment near the shore, and excessive growth of undesirable organisms--the combination of all these aspects has very serious consequences.
Large-scale accidental discharges of liquid petroleum products are an important cause of pollution along shorelines. The most spectacular involve the supertankers used for oil transport, but many other ships also spill oil, and offshore drilling operations contribute a large share of the pollution. One estimate is that of every million tons of oil shipped, one ton is spilled. Some of the largest spills thus far recorded involve the tanker Amoco Cadiz off the French coast in 1978 (1.6 million barrels of crude oil) and the Ixtoc I oil well in the Gulf of Mexico in 1979 (3.3 million barrels). The largest spill in the U.S. (240,000 barrels) was that of the tanker Exxon Valdez in Prince William Sound, Gulf of Alaska, in March 1989. Within a week, under high winds, this spill had become a 6700-sq-km (2600-sq-mi) slick that endangered wildlife and fisheries in the entire gulf area.
The oil spills in the Persian Gulf in 1983, during the Iran-Iraq conflict, and in 1991, during the Persian Gulf War, resulted in enormous damage to the entire area, especially to the marine life.
In the U.S. the first federal legislation addressing water quality issues was the Rivers and Harbors Act near the end of the 19th century; it barred the dumping in navigable waters of solid refuse (not liquids) that would hamper navigation. The intentional discharge of oil by vessels coastal waters was banned by the Oil Pollution Act of 1924.
The Federal Water Pollution Control Act of 1948 called for studies and other programs aimed at lessening pollution of interstate waters and upgrading the condition of surface and underground waters. Subsequent legislation expanded the initiative and added assessment and regulatory powers. A 1961 measure, for example, required federal agencies planning reservoirs and the like to take water quality into account in managing stream flow. The Water Quality Act of 1965 created the Water Pollution Control Administration in the Department of the Interior and required states to establish water quality standards, with an eye toward setting goals for interstate waters. The Clean Water Restoration Act of 1966 mandated a comprehensive study of pollution in estuaries and estuarine zones and barred the discharge without permit of oil into the navigable waters. Growing concern over environmental problems, highlighted by such incidents as a 1969 fire on the polluted Cuyahoga River in Cleveland, Ohio, prompted the creation in 1970 of the EPA, which became the primary federal body dealing with water pollution. The Water Quality Improvement Act of 1970 tightened restrictions on oil discharges and provided for demonstration projects on controlling mine water pollution and pollution in the watersheds of the Great Lakes.Major amendments enhancing the Federal Water Pollution Control Act were passed in 1972 and again in 1977, and the law as revised came to be known as the Clean Water Act. The amendments established stringent controls and cleanup deadlines for industrial and municipal pollution, shifting the emphasis from the regulation of general water quality to the setting of rigorous standards for wastewater in particular. A system of issuing permits for discharges into U.S. waters was also created, and provisions were added to strengthen the suppression of toxic water pollutants. While administration of the act was the responsibility of the EPA, day-to-day implementation was the task of state and local governments. The Clean Water Act also authorized federal aid for the building of municipal wastewater plants. Amendments in 1987 moved beyond a previous emphasis on controlling point sources of pollution to focus on nonpoint sources as well, making extensive use of voluntary programs.
Among other U.S. laws pertaining to clean water, the Safe Drinking Water Act, passed by Congress in 1974 and later amended, instituted health-based drinking-water standards for all public water systems and supplemented a focus on water treatment with attention to protection of water sources. The Ocean Dumping Ban Act of 1988 (which amended the Marine Protection, Research, and Sanctuaries Act of 1972) banned the dumping into the ocean of sewage sludge and industrial waste, except when allowed by an EPA permit. The Coastal Zone Management Act as amended in 1990 included provisions aimed at reducing pollution in coastal waters from nonpoint sources. Clean-air legislation has benefited water quality in the U.S. by helping to control acid rain and by reducing the atmospheric deposition of pollutants in bodies of water (see Air Pollution).
Since groundwater and surface waters are not necessarily confined by national borders, water quality concerns have often been addressed in agreements between nations, notably bilateral and multilateral pacts concerning the use of transboundary rivers and other waters. Efforts have also been made at more far-ranging international accords, but binding agreements mandating effective global controls have been slow to materialize. A Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter was adopted in 1972 in London and entered into force in 1975. As of late 2006, more than 80 nations, including the U.S., had ratified it or acceded to it. The London Convention, as it is commonly known, bars the deliberate disposal of certain materials from vessels, aircraft, and platforms and does not deal with the discharge of wastes from land-based sources or the incidental release of wastes during normal vessel operation. A more restrictive protocol was adopted in 1996 and went into effect in early 2006; the U.S. was not among its approximately 30 contracting parties.
The first international agreement aimed at oil pollution from ships was adopted at a 1954 conference in the United Kingdom. This International Convention for the Prevention of Pollution of the Sea by Oil, or OILPOL for short, came into force in 1958. It focused mainly on pollution resulting from routine tanker operations and from release of oily wastes. A need for more stringent measures gradually became apparent, highlighted in 1967 when the tanker Torrey Canyon ran aground in the English Channel and spilled 120,000 tons of crude oil--the most serious marine oil pollution incident recorded up to that time. OILPOL was essentially supplanted by MARIPOL, the International Convention for the Prevention of Pollution from Ships, adopted in 1973 at the International Maritime Organization and modified in 1978 by a protocol. MARIPOL, which entered into force in stages between 1983 and 2005, is today the principal accord dealing with prevention of marine pollution by vessels from operational or accidental causes. It extends not only to oil but also to chemicals, harmful substances in packaged form, sewage, and garbage; the 1978 protocol added new restrictions on tanker design and operation. As of 2006, the contracting parties to MARIPOL and its five initial annexes included more than 100 nations, among them the U.S. (Fewer than 40 nations were parties to a sixth annex, a protocol on air pollution from ships, that was adopted in 1997 and went into effect in 2005.)
Among other notable international efforts addressing water quality concerns, the United Nations General Assembly in 1997 adopted a Convention on the Law of the Non-Navigational Uses of International Watercourses. The document was intended to provide, among other things, a framework for action by watercourse states to prevent, reduce, and control pollution, but it met extensive criticism for vague and contradictory phrasing. As of 2006, it was not close to reaching the minimum of 35 ratifications or accessions required for it to go into effect.