Water pollution
Water pollution is the contamination of water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources. These are sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Water pollution may affect either surface water or groundwater. This form of pollution can lead to many problems. One is the degradation of aquatic ecosystems. Another is spreading water-borne diseases when people use polluted water for drinking or irrigation. Water pollution also reduces the ecosystem services such as drinking water provided by the water resource.
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. An example is agricultural runoff. Pollution is the result of the cumulative effect over time. Pollution may take many forms. One would is toxic substances such as oil, metals, plastics, pesticides, persistent organic pollutants, and industrial waste products. Another is stressful conditions such as changes of pH, hypoxia or anoxia, increased temperatures, excessive turbidity, or changes of salinity). The introduction of pathogenic organisms is another. Contaminants may include organic and inorganic substances. 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.
Definition
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." Water is typically referred to as polluted when it is impaired by anthropogenic contaminants. Due to these contaminants, it either no longer supports a certain human use, such as drinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish.Contaminants
Contaminants with an origin in sewage
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.
- Disinfection by-products found in chemically disinfected drinking water.
- Hormones 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.
- Insecticides and herbicides, often from agricultural runoff.
- Pathogens like Hepatovirus A
Pathogens
Bacteria, viruses, protozoans and parasitic worms are examples of pathogens that can be found in wastewater. 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 of fecal contamination of water samples most commonly used are total coliforms or fecal coliforms, the latter also referred to as thermotolerant coliforms, such as Escherichia coli.Pathogens can produce waterborne diseases in either human or animal hosts. 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, and parasitic worms including the Schistosoma'' type.
The source of high levels of pathogens in water bodies can be from human feces, sewage, blackwater, or manure that has found its way into the water body. The cause for this can be lack of sanitation procedures or poorly functioning on-site sanitation systems, sewage treatment plants without disinfection steps, sanitary sewer overflows and combined sewer overflows during storm events and intensive agriculture.
Organic compounds
Organic substances that enter water bodies are often toxic.- Petroleum hydrocarbons, including fuels and lubricants, and fuel combustion byproducts, from oil spills or storm water runoff
- Volatile organic compounds, such as improperly stored industrial solvents. Problematic species are organochlorides such as polychlorinated biphenyl and trichloroethylene, a common solvent.
Inorganic contaminants
Inorganic water pollutants include:- Ammonia from food processing waste
- Heavy metals from motor vehicles and acid mine drainage
- Nitrates and phosphates, from sewage and agriculture
- Silt in runoff from construction sites or sewage, logging, slash and burn practices land clearing sites
- Salt: Freshwater salinization is the process of salty runoff contaminating freshwater ecosystems. Human-induced salinization is termed as secondary salinization, with the use of de-icing road salts as the most common form of runoff.
Pharmaceutical pollutants
- Environmental persistent pharmaceutical pollutants, which can include various pharmaceutical drugs and their metabolites, such as antidepressant drugs, antibiotics or the contraceptive pill.
- Metabolites of illicit drugs, for example methamphetamine and ecstasy.
Solid waste and plastics
Microplastics persist in the environment at high levels, particularly in aquatic and marine ecosystems, where they cause water pollution. 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester, acrylic, or nylon-based clothing, often during the washing process.
Stormwater, untreated sewage and wind are the primary conduits for microplastics from land to sea. Synthetic fabrics, tyres, and city dust are the most common sources of microplastics. These three sources account for more than 80% of all microplastic contamination.
Types of surface water pollution
Surface water pollution includes pollution of rivers, lakes and oceans. A subset of surface water pollution is marine pollution which affects the oceans. Nutrient pollution refers to contamination by excessive inputs of nutrients.Globally, about 4.5 billion people do not have safely managed sanitation as of 2017, according to an estimate by the Joint Monitoring Programme for Water Supply and Sanitation. Lack of access to sanitation is concerning and often leads to water pollution, e.g. via the practice of open defecation: during rain events or floods, the human feces are moved from the ground where they were deposited into surface waters. Simple pit latrines may also get flooded during rain events.
As of 2022, Europe and Central Asia account for around 16% of global microplastics discharge into the seas, and although management of plastic waste and its recycling is improving globally, the absolute amount of plastic pollution continues to increase unabated due to the large amount of plastic that is being produced and disposed of. Even if sea plastic pollution were to stop entirely, microplastic contamination of the surface ocean would be projected to continue to increase.
Marine pollution
Nutrient pollution
Thermal pollution
Elevated water temperatures decrease oxygen levels, which can kill fish and alter food chain composition, reduce species biodiversity, and foster invasion by new thermophilic species.Biological pollution
The introduction of aquatic invasive organisms is a form of water pollution as well. It causes biological pollution.Groundwater pollution
In many areas of the world, groundwater pollution poses a hazard to the wellbeing of people and ecosystems. One-quarter of the world's population depends on groundwater for drinking, yet concentrated recharging is known to carry short-lived contaminants into carbonate aquifers and jeopardize the purity of those waters.Pollution from point sources
refers to contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city storm drain.The U.S. Clean Water Act defines point source for regulatory enforcement purposes. The CWA definition of point source was amended in 1987 to include municipal storm sewer systems, as well as industrial storm water, such as from construction sites.