Pollution, Water

Sources of Water Pollutants

When pollutants are discharged to bodies of water directly or indirectly, it causes water pollution. According to the Environmental Protection Agency (EPA), water pollutants come from two sources: point and nonpoint. Direct discharge of pollutants to bodies of water is mainly from point sources such as municipal storm sewer systems, sewage treatment plants, factories, ships, and construction sites. Examples of direct pollutants include food-processing wastes (fats and grease), personal hygiene and cosmetic products, shipwreck debris, silt from eroded soil in construction sites, and other trashes. Nonpoint sources are indirect sources of pollution and are more diffuse, as they do not originate from a single discrete source. Agricultural runoff; runoff coming from other land uses such as urban, forest, and mining activities; and paved roads are nonpoint source pollutants. Crop fertilizers, manures, pesticides, and insecticides that are washed away with runoff into streams and other bodies of water cause water pollution. Animal or bird (wild or domestic) excreta over pastures, forests, or other land uses also wash away into streams as nonpoint source pollution. Human and animal excreta discharged directly into bodies of water are major point source pollutants.

Specific contaminants that cause water pollution include a wide spectrum of chemicals and pathogens. Both organic and inorganic chemicals are water pollution contaminants. Common chemical contaminants include detergents; disinfection byproducts; petroleum byproducts (gasoline, diesel, jet fuels, kerosene, other fuel oil, lubricants, and fuel-combustion byproducts); industrial solvents; chlorinated solvents; sulfur dioxide and other chemical wastes from industrial sources; heavy metals from motor vehicles via urban storm-water runoff; and nutrients (e.g., nitrogen, phosphorous, and potassium) from fertilizers.

Increased pathogen count in water also causes water pollution. Fecal coliform bacteria are the common indicator of water pollution. They are generally present in human, animal, or bird excreta. Other pathogens found in polluted water are Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia, salmonella, norovirus and other viruses, and other parasitic worms.

Effects of Pollutants in Water

Other than making water unsuitable for human or animal consumption, these water pollutants cause unfavorable conditions for aquatic plants and animals. Physical or sensory changes such as elevated temperature and discoloration occur in the water. Elevated water temperature decreases the amount of dissolved oxygen (DO) in water, thus limiting the supply of oxygen to aquatic animals. One of the sources of water temperature elevation is urban runoff. Increased nutrient levels cause algal bloom in surface water and decreases sunlight interaction. Excess nutrients from algal death and decomposition decreases the amount of DO in water, causing death of aquatic animals. Because of these water pollutants, the pH level in water changes, harming aquatic life. Global warming is believed to cause the acidification (lowering of pH) of ocean water because of the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere. Table 1 provides a list

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