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Water pollution is a contamination of natural water bodies by chemical, physical, radio active substances. Water pollution is a large set of adverse effects upon bodies of water such as lakes, rivers, oceans, and groundwater caused by human activities.

Water pollution has many causes and characteristics. Natural phenomena such as volcanoes, algae blooms, storms, earthquakes, runoff, decay of vegetation and oil seeps can cause changes in water quality and the ecological status of water. Increases in nutrient loading may lead to eutrophication. Organic wastes such as sewage impose high oxygen demands on the receiving water leading to oxygen depletion with potentially severe impacts on the whole eco-system. Industries discharge a variety of pollutants in their wastewater including heavy metals, resin pellets, organic toxins, oils, nutrients, and solids. Discharges can also have thermal effects, especially those from power stations, and these too reduce the available oxygen. Silt-bearing runoff from many activities including construction sites, deforestation and agriculture can inhibit the penetration of sunlight through the water column, restricting photosynthesis and causing blanketing of the lake or river bed, in turn damaging ecological systems.

Pollutants in water include a wide spectrum of chemicals, pathogens, and physical chemistry or sensory changes. Some occur occur naturally, but most result from human activity. Many of the chemical substances are toxic. Pathogens can produce waterborne diseases in either human or animal hosts. Alteration of water's physical chemistry include acidity, electrical conductivity, temperature, and eutrophication. Eutrophication is the fertilisation of surface water by nutrients that were previously scarce. Even many of the municipal water supplies in developed countries can present health risks. Water pollution is a major problem in the global context. It has been suggested that it is the leading worldwide cause of deaths and diseases,and that it accounts for the deaths of more than 14,000 people daily.

  • One gallon of oil can pollute 1,000,000 gallons of H2O and a 8 acre lake
  • One barrel of oil can pollute 42,000,000 gallons of water and a 336 acre lake
  • One gallon of paint can pollute 250,000 gallons of water
  • One gallon of gasoline can pollute 750,000 gallons of water
  • One gallon of road salt can pollute 3,840 gallons of water
  • One gallon of trichloroethylene can pollute more than 192,000,000 gallons of water
  • One gallon of Hg can pollute 1,920,000,000 gallons of water and a 24 square mile lake
  • One ton of salt can pollute 400,000 gallons of water
  • One ton of coal can pollute 220,000,000 gallons of water
  • One ton of mercury can pollute a 81,000 square kilometer lake
  • One metric ton of Pb can pollute 20 gigaliters of water
  • One metric ton of Hg can pollute a 31,250 square mile lake or 5,000,000,000,000 gallons of water
  • One metric ton of Ag can pollute 5,000,000,000,000 gallons of water and a 62,500 square mile lake
  • Mercury from one thermometer can pollute 5,000,000 gallons of water (6 Olympic sized swimming pools)
  • Mercury from one fluorescent light bulb can pollute 6,000 gallons of water
  • One American mine can pollute 675,000,000 gallons of water each year
  • One ton of Fabric can pollute a 300 cubic meter lake
  • One gallon of diazinon can pollute 1,920,000,000 gallons of water
  • One cellphone can pollute 34,800 gallons of water
  • One kWh of Energy can pollute a 1,500/19 cubic meter lake
  • One btu of Energy can pollute 210/29 gallons of water
  • One ton of paper can pollute 20,000 gallons of water
  • One gallon of antifreeze can pollute 10,000 gallons of water


Some organic water pollutants are:

  • Insecticides and herbicides, a huge range of organohalides and other chemicals
  • Bacteria, sometimes from sewage produced by livestock operations
  • Food processing waste, including pathogens
  • Tree and brush debris from logging operations
  • VOCs (volatile organic compounds), such as industrial solvents, from improper storage
  • DNAPLs (dense non-aqueous phase liquids), such as chlorinated solvents, which may fall at the bottom of reservoirs, since they don't mix well with water and are more dense
  • Petroleum Hydrocarbons including fuels (gasoline, diesel, jet fuels, and fuel oils) and lubricants (motor oil) from oil field operations, refineries, pipelines, retail service station's underground storage tanks, and transfer operations. Note: VOCs include gasoline-range hydrocarbons.
  • Detergents
  • Various chemical compounds found in personal hygiene and cosmetic products

Some inorganic water pollutants include:

  • Heavy metals including acid mine drainage
  • Acidity caused by industrial discharges (especially sulfur dioxide from power plants)
  • Alkalinity, bicarbonate, HCO3-, or other ions, from agricultural runoff
  • Pre-production industrial raw resin pellets, an industrial pollutant
  • Chemical waste as industrial by products
  • Fertilizers, in runoff from agriculture including nitrates and phosphates
  • Silt in surface runoff from construction sites, logging, slash and burn practices or land clearing sites

Transport and chemical reactions of water pollutants

Most water pollutants are eventually carried by the rivers into the oceans. In some areas of the world the influence can be traced hundred miles from the mouth by studies using hydrology transport models. Advanced computer models such as SWMM or the DSSAM Model have been used in many locations worldwide to examine the fate of pollutants in aquatic systems. Indicator filter feeding species such as copepods have also been used to study pollutant fates in the New York Bight, for example. The highest toxin loads are not directly at the mouth of the Hudson River, but 100 kilometers south, since several days are required for incorporation into planktonic tissue. The Hudson discharge flows south along the coast due to coriolis force. Further south then are areas of oxygen depletion, caused by chemicals using up oxygen and by algae blooms, caused by excess nutrients from algal cell death and decomposition. Fish and shellfish kills have been reported, because toxins climb the foodchain after small fish consume copepods, then large fish eat smaller fish, etc. Each successive step up the food chain causes a stepwise concentration of pollutants such as heavy metals (e.g. mercury (element)|mercury) and persistent organic pollutants. This is known as biomagnification which is occasionally used interchangeably with bioaccumulation.

The big gyres in the oceans trap floating plastic debris. The North Pacific Gyre for example has collected the so-called Great Pacific Garbage Patch that is now estimated at two times the size of Texas. Many of these long-lasting pieces wind up in the stomachs of marine birds and animals. This results in obstruction of digestive pathways which leads to reduced appetite or even starvation.

Many chemicals undergo reactive decay or chemically change especially over long periods of time in groundwater reservoirs. A noteworthy class of such chemicals are the chlorinated hydrocarbons such as trichloroethylene (used in industrial metal degreasing and electronics manufacturing) and tetrachloroethylene used in the dry cleaning industry (note latest advances in liquid carbon dioxide in dry cleaning that avoids all use of chemicals). Both of these chemicals, which are carcinogens themselves, undergo partial decomposition reactions, leading to new hazardous chemicals

Groundwater pollution is much more difficult to abate than surface pollution because groundwater can move great distances through unseen aquifers. Non-porous aquifers such as clay partially purify water of bacteria by simple filtration (adsorption and absorption), dilution, and, in some cases, chemical reactions and biological activity: however, in some cases, the pollutants merely transform to soil contaminants. Groundwater that moves through cracks and caverns is not filtered and can be transported as easily as surface water. This can be aggravated by the human tendency to use natural sinkholes as dumps in areas of Karst topography.

There are a variety of secondary effects stemming not from the original pollutant, but a derivative condition. Some of these secondary impacts are:

  • Silt bearing surface runoff can inhibit the penetration of sunlight through the water column, hampering photosynthesis in aquatic plants.
  • Thermal pollution can induce fish kills and invasion by new thermophilic species

Sampling & Monitoring

Water Sampling can take several forms depending on the accuracy needed and the characteristics of the contaminant. Many contamination events are temporal and most commonly in association with rain events. For this reason 'grab' samples can be used as indicators, but are often inadequate for fully accessing contaminant concerns in a water body. Scientists gathering this type of data often employ auto-sampler devices that pump increments of water at either time or discharge intervals.

Regulatory framework

In the United Kingdom there are common law rights (civil rights) to protect the passage of water across land unfettered in either quality of quantity. Criminal laws dating back to the 16th century exercised some control over water pollution but it was not until the River (Prevention of pollution )Acts 1951 - 1961 were enacted that any systematic control over water pollution was established. These laws were strengthened and extended in the Control of Pollution Act 1984 which has since been updated and modified by a series of further acts. It is a criminal offense to either pollute a lake, river, groundwater or the sea or to discharge any liquid into such water bodies without proper authority. In England and Wales such permission can only be issued by the Environment Agency and in Scotland by Scottish Environment Protection Agency.

In the USA, concern over water pollution resulted in the enactment of state anti-pollution laws in the latter half of the 19th century, and federal legislation enacted in 1899. The Refuse Act of the federal Rivers and Harbors Act of 1899 prohibits the disposal of any refuse matter from into either the nation's navigable rivers, lakes, streams, and other navigable bodies of water, or any tributary to such waters, unless one has first obtained a permit. The Water Pollution Control Act, passed in 1948, gave authority to the Surgeon General to reduce water pollution.

Growing public awareness and concern for controlling water pollution led to enactment of the Federal Water Pollution Control Act Amendments of 1972. As amended in 1977, this law became commonly known as the Clean Water Act. The Act established the basic mechanisms for regulating contaminant discharge. It established the authority for the United States Environmental Protection Agency to implement wastewater standards for industry. The Clean Water Act also continued requirements to set water quality standards for all contaminants in surface waters.