Water Pollution

• Water pollution

  Any physical, biological, or chemical change in water quality that adversely affects living organisms or makes water unsuitable for desired uses
• Sources of water pollution

  • All industries that generate wastewater
  • Scattered or diffuse sources like runoff from farm fields, golf courses, construction sites, etc.
  • Atmospheric deposition of contaminants
• Major categories of water pollutants

  • Causes health problems (infectious agents, organic chemicals, inorganic chemicals, radioactive materials)
  • Causes ecosystem disruption (sediment, plant nutrients, oxygen-demanding wastes, thermal)
• Pathogenic organisms

  • The most serious water pollutants in terms of human health worldwide
  • At least 25 million deaths each year blamed on water-related diseases
  • Main source is untreated or improperly treated human and animal wastes
• Oxygen levels

  • Indicator of water quality and the kinds of life it will support
  • Water with less than 2 ppm oxygen will support mainly worms, bacteria, fungi, and other detritus feeders and decomposers
• Biochemical oxygen demand (BOD)


  Amount of dissolved oxygen needed for microorganisms to decompose organic matter in water
• Chemical oxygen demand (COD)


  Uses a strong oxidizing agent to completely breakdown all organic matter in a water sample
• Dissolved oxygen (DO)

  Directly measures oxygen content of water, best for indicating health of aquatic system
• Oxygen sag

  Oxygen decline downstream from pollution source
• Eutrophication


  Increase in nutrient levels and biological productivity, often caused by human activities
• Eutrophication

  • Calumpang River in the Philippines
• Eutrophication


  • Elevated phosphorus and nitrogen levels stimulate algal blooms and thick aquatic plant growth
  • Bacterial populations increase, water becomes cloudy and has unpleasant tastes and odors
  • Collapse of aquatic ecosystem can result
• Inorganic pollutants

  • Toxic chemicals like heavy metals that are released from rocks, mining, and other human activities
  • Highly persistent and can accumulate in food webs
• Mercury released from coal-burning power plants is the most widespread toxic metal contamination problem in North America
• Salinization affects 20% of the world's irrigated farmland, decreasing yields significantly
• Arsenic in groundwater is a major threat to human populations in West Bengal, India and eastern Bangladesh
• Rapid population growth, industrialization, and intensification of agriculture are increasing water pollution globally
• Mine drainage and leaching of mining wastes are serious sources of metal pollution in water
• Some soils contain naturally high concentrations of soluble salts, including toxic selenium and arsenic
• Salts, such as sodium chloride, that are non-toxic at low concentrations also can be mobilized by irrigation and concentrated by evaporation, reaching levels that are toxic for many plants and animals
• Globally, 20% of the world's irrigated farmland is estimated to be affected by salinization, and half that land has enough salt buildup to decrease yields significantly
• The largest human population threatened by naturally occurring arsenic in groundwater is in West Bengal, India, and eastern Bangladesh. Arsenic occurs naturally in the sediments that make up the Ganges River delta
• Rapid population growth, industrialization, and intensification of irrigated agriculture have depleted or polluted limited surface water supplies. In an effort to provide clean drinking water for local residents, thousands of tube wells were sunk in the 1960s throughout the area. Much of this humanitarian effort was financed by loans from the World Bank
• By the 1980s health workers became aware of widespread signs of chronic arsenic poisoning among Bengali villagers. Symptoms include watery and inflamed eyes, gastrointestinal cramps, gradual loss of strength, dry skin and skin tumors, anemia, confusion, and eventually death. Health workers estimate that the total number of potential victims in India and Bangladesh may exceed 100 million people. Fortunately, arsenic can be removed from water supplies relatively easily and cheaply
• Acids are released as by-products of industrial processes, such as leather tanning, metal smelting and plating, petroleum distillation, and organic chemical synthesis
• Coal mining is an especially important source of acid water pollution
• Where soils are rich in such alkaline material as limestones, atmospheric acids have little effect because they are neutralized
• Aquatic damage due to acid precipitation has been reported in about 200 lakes in the Adirondack Mountains of New York State and in several thousand lakes in eastern Quebec, Canada
• Game fish, amphibians, and sensitive aquatic insects are generally the first to be killed by increased acid levels in the water
• If acidification is severe enough, aquatic life is limited to a few resistant species of mosses and fungi
• Increased acidity may result in leaching of toxic metals, especially aluminum, from soil and rocks, making water unfit for drinking or irrigation, as well
• Human activities may themselves reduce natural recharge, so ground water consumed may not be replaced, even slowly
• Organic Pollutants

  • Drugs
  • Pesticides
  • Other industrial substances
• Thousands of different natural and synthetic organic chemicals are used in the chemical industry to make pesticides, plastics, pharmaceuticals, pigments, and other products that we use in everyday life
• Exposure to very low concentrations can cause birth defects, genetic disorders, and cancer
• Some can persist in the environment because they are resistant to degradation and toxic to organisms that ingest them
• Contamination of surface waters and groundwater by these chemicals is a serious threat to human health
• The two most important sources of toxic organic chemicals in water are improper disposal of industrial and household wastes and runoff of pesticides from farm fields, forests, roadsides, golf courses, and other places where they are used in large quantities
• The U.S. EPA estimates that 500,000 metric tons of pesticides are used in the United States each year. Much of this material washes into the nearest waterway, where it passes through ecosystems and may accumulate in high levels in non target organisms
• Countless other organic compounds also enter our water. People simply dump unwanted food, medicines, and health supplements down the toilet or sink. More often we consume more than our bodies can absorb, and we excrete the excess, which passes through sewage treatment facilities relatively unchanged