pollutants

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Wide range of pollutants degrade world’s water

POLLUTANT

PRIMARY SOURCE

EFFECTS

Organic matter

Industrial wastewater and domestic sewage

Depletes oxygen from the water column as it decomposes, stressing or suffocating aquatic life

Excess nutrients (nitrates, phosphorous)

Runoff from agricultural lands and urban areas

Overstimulates growth of algae (a process called eutrophication), which then decomposes, robbing water of oxygen, and harming aquatic life.  High levels of nitrates in drinking water lead to illness in humans

Heavy metals

Industries and mining sites

Persists in freshwater environments, like river sediments and wetlands for long periods.  Accumulates in the tissues of fish and shellfish. Toxic to both aquatic organisms and humans who eat them

Microbial contaminants (e.g., cryptosporidium, cholera, and other bacteria, amoebae, etc.)

Domestic sewage, cattle, natural sources

Spreads infectious diseases through contaminated water supplies, causing millions of cases of diarrheal diseases and intestinal parasites, and providing one of the principal causes of childhood mortality in the developing world

Toxic organic compounds (oil, pesticides, some plastics, industrial chemicals)

Wide variety of sources, from industrial sites, to automobiles, to farmers, and home gardeners

Displays a range of toxic effects in aquatic fauna and humans, from mild immune suppression, to acute poisoning, or reproductive failure

Dissolved salts (salinization)

Leached from alkaline soils by over-irrigation, or drawn into coastal aquifers from overdrafting of groundwater

Leads to salt build-up in soils, which kills crops or cuts yields.  Renders freshwater supplies undrinkable

Acid precipitation or acidic runoff

Deposition of sulphate particles, mostly from coal combustion.  Acid runoff from mine tailings and sites

Acidifies lakes and streams, which harms or kills aquatic organisms and leaches heavy metals such as aluminum from soils into water bodies

Silt and suspended particles

Soil erosion and construction activities in watersheds

Reduces water quality for drinking and recreation and degrades aquatic habitats by smothering them with silt, disrupting spawning, and interfering with feeding

Thermal pollution

Fragmentation of rivers by dams and reservoirs, slowing water and allowing it to warm.  Industrial uses such as cooling towers

Affects oxygen levels and decomposition rate of organic matter in the water column.  May shift the species composition of a river or lake

Source: World Resources Institute / wri.org