Courtesy : Wikipedia

water pollution

Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, in such a manner that negatively affects its legitimate uses.^[1]: 6 Water pollution reduces the ability of the body of water to provide the ecosystem services that it would otherwise provide. Water bodies include for example lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants are introduced into these water bodies. Water pollution can usually be attributed to one of four sources: sewage, industry, agriculture, and urban runoff including stormwater.^[2] For example, releasing inadequately treated wastewater into natural waters can lead to degradation of these aquatic ecosystems. Water pollution can also lead to water-borne diseases for people using polluted water for drinking, bathing, washing or irrigation.^[3] Supplying clean drinking water is an important ecosystem service provided by some freshwater systems, but approximately 785 million people in the world do not have access to clean drinking water because of pollution.^[4]

Water pollution can be classified as surface water pollution (for example lakes, streams, estuaries, and parts of the ocean in marine pollution) or groundwater pollution. Sources of water pollution are either point sources or non-point sources. Point sources have one identifiable cause, such as a storm drain, a wastewater treatment plant or an oil spill. Non-point sources are more diffuse, such as agricultural runoff.^[5] Pollution is the result of the cumulative effect over time.

Pollution may take the form of toxic substances (e.g., oil, metals, plastics, pesticides, persistent organic pollutants, industrial waste products), stressful conditions (e.g., changes of pH, hypoxia or anoxia, stressful temperatures, excessive turbidity, unpleasant taste or odor, and changes of salinity), or pathogenic organisms. Contaminants may include organic and inorganic substances. Heat can also be a pollutant, and this is called thermal pollution. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers.

Control of water pollution requires appropriate infrastructure and management plans as well as legislation. Technology solutions can include improving sanitation, sewage treatment, industrial wastewater treatment, agricultural wastewater treatment, erosion control, sediment control and control of urban runoff (including stormwater management). Effective control of urban runoff includes reducing speed and quantity of flow.

A practical definition of water pollution is: “Water pollution is the addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses”.^[1]: 6 Therefore, pollution is associated with concepts attributed to humans, namely the negative alterations and the uses of the water body. Water is typically referred to as polluted when it is impaired by anthropogenic contaminants. Due to these contaminants it either does not support a human use, such as drinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish.

Contaminants and their sources

Overview

If the water pollution stems from sewage (municipal wastewater), the main pollutants are: suspended solids, biodegradable organic matter, nutrients and pathogenic organisms.^[1]: 6

Pathogens from sewage and agriculture

Poster to teach people in South Asia about human activities leading to the pollution of water sources

Disease-causing microorganisms are referred to as pathogens. The major groups of pathogenic organisms are: (a) bacteria, (b) viruses, (c) protozoans and (d) helminths.^[1]: 47 In practice, indicator organisms are used to investigate pathogenic pollution of water because the detection of pathogenic organisms in water sample is difficult and costly, because of their low concentrations. The indicators (bacterial indicator) of fecal contamination of water samples most commonly used are: total coliforms (TC), fecal coliforms (FC) or thermotolerant coliforms, escherichia coli (EC).^[1]: 47

Pathogens can produce waterborne diseases in either human or animal hosts.^[7] Some microorganisms sometimes found in contaminated surface waters that have caused human health problems include: Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia, Salmonella, norovirus and other viruses, parasitic worms including the Schistosoma type.^[8]

The source of high levels of pathogens in water bodies can be from human feces (due to open defecation), sewage, blackwater, manure that has found its way into the water body. The cause for this can be lack of sanitation or poorly functioning on-site sanitation systems (septic tanks, pit latrines), sewage treatment plants without disinfection steps, sanitary sewer overflows and combined sewer overflows (CSOs)^[9] during storm events and intensive agriculture (poorly managed livestock operations).

Muddy river polluted by sediment.

Non-biodegradable organic compounds

Non-biodegradable organic substances can enter water bodies from a variety of sources, for example industrial wastewater. Many of these chemical substances are toxic.^[10]: 229

• Chemicals from insecticides and herbicides.
• Petroleum hydrocarbons, including fuels (gasoline, diesel fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel combustion byproducts, from oil spills or storm water runoff^[11]
• Volatile organic compounds, such as industrial solvents, from improper storage.
• Persistent organic pollutants, for example per- and polyfluoroalkyl substances (PFAS),^[12][13]
• Organochlorides, polychlorinated biphenyl (PCBs), trichloroethylene, perchlorate (these are currently or were in the past used as pesticides, solvents, pharmaceuticals, and industrial chemicals).

The following compounds can all reach water bodies via raw sewage or even treated sewage discharges:

• Various chemical compounds found in personal hygiene and cosmetic products.
• Environmental persistent pharmaceutical pollutants, which can include various pharmaceutical drugs and their metabolites (see also drug pollution), such as antidepressant drugs, antibiotics or the contraceptive pill.
• Metabolites of illicit drugs (see also wastewater epidemiology), for example methamphetamine and ecstasy.^[14][15]
• Disinfection by-products found in chemically disinfected drinking water (whilst these chemicals can be a pollutant in the water distribution network, they are fairly volatile and therefore not usually found in environmental waters).^[16]
• Hormones (from animal husbandry and residue from human hormonal contraception methods) and synthetic materials such as phthalates that mimic hormones in their action. These can have adverse impacts even at very low concentrations on the natural biota and potentially on humans if the water is treated and utilized for drinking water.^[17][18][19]

Persistent organic pollutants

Inorganic contaminants

Bauxite residue is an industrial waste that is dangerously alkaline and can lead to water pollution if not managed appropriately (photo from Stade, Germany).

Inorganic water pollutants include for example:

• Acidity caused by industrial discharges (especially sulfur dioxide from power plants) or by increased carbon dioxide concentrations in the atmosphere (see also ocean acidification). In industrialized areas, acid rain has in the past resulted in pollution of lakes and rivers due to air pollution with dissolved oxides of sulfur and nitrogen.^{[citation needed]}
• Ammonia from food processing waste
• Heavy metals from motor vehicles (via urban storm water runoff)^[11][21] and acid mine drainage
• Nitrates and phosphates, from sewage and agriculture (see nutrient pollution)
• Silt (sediment) in runoff from construction sites or sewage, logging, slash and burn practices or land clearing sites.