Heavy metals are toxic and include many metal pollutants that could have potentially harmful effects on human health and aquatic ecosystems. Common examples include cadmium, nickel, arsenic, lead, vanadium, mercury, and selenium. Typical sources of metal pollutants include wastes from domestic, industry, agriculture, urban, and mining drains. Acids are inorganic water pollutants caused by industrial discharges, especially sulfur dioxide from industrial power plants, drainage from mines, wastes from industry, and aerial acid deposition. Acids have the potential of causing harm to aquatic ecosystems via the mobilization of toxic heavy metal pollutants.
Organic chemicals such as insecticides, herbicides, petroleum hydrocarbons, detergents, and a range of volatile organic compounds such as solvents discharged into aquatic ecosystems have the potential of altering the integrity of natural waters. This variety of chemicals regarded as water pollutants arises from agricultural use of pesticides, especially insecticides and herbicides, industrial wastes, marine oil spillage, and domestic wastes. They are potentially harmful to human health and aquatic organisms. Nutrients arising from sewage and agricultural use of fertilizers may cause eutrophication in aquatic ecosystems.
Although nutrients are elements essential for the growth of living organisms, human-caused contaminations can greatly enhance the presence of nutrients (especially nitrogen and phosphorus compounds), leading to anthropogenic or cultural eutrophication. Continuous nutrient loading to aquatic systems could ultimately increase the phytoplankton population, resulting in algal bloom, by providing more food for the algae than is normally available. Nutrients may affect human health. Excessive algal population in water has the potential of unbalancing the food chain, discoloration of water, and reduction in the quantity of light radiation that is available to aquatic life. However, when the algae dies, the rotting algae could produce a strong, unpleasant smell and the remains could be toxic to aquatic fauna and flora. This process could also result in depletion of dissolved oxygen in water.
There are several sources of water pollutants, and these are domestic and industrial wastewaters, agricultural runoff water, and other nonpoint sources. Domestic wastes commonly carry organic matter, microbiological contaminants, and sometimes physical and chemical pollutants. Industrial wastes contain mostly chemical and radioactive pollutants, while agricultural run-off water may carry mainly nutrients, pesticides, and heavy metals. Moreover, water pollution can be broadly classified into different types and these include microbiological, chemical, physical, and thermal water pollution.
Biological hazards associated with water pollution include disease-causing (pathogenic) microorganisms, like parasites, bacteria, and viruses. People exposed to biologically contaminated waters can become sick from drinking, washing, or swimming. Disease-causing pathogens commonly associated with fecal contamination of water include Shigella dysenteriae, Salmonella typhi, Salmonella paratyphi, Vibrio cholerae, Entamoeba histolytica and poliomyelitis virus responsible for causing bacterial dysentery, typhoid fever, paratyphoid fever, cholera, amoebic dysentery, and infantile paralysis, respectively. Also, the consumption of microbe-contaminated seafood, especially shellfish, could lead to outbreaks of food poisoning.
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