Chemistry · Ch 15 — Environmental Chemistry
Causes of Water Pollution
Causes of Water Pollution
This section develops the mechanisms behind three broad causes of water pollution introduced in section 15.5's pollutant table. Microbiological contamination comes from untreated or poorly treated domestic sewage entering water bodies, introducing pathogenic bacteria, viruses and protozoa that cause waterborne diseases such as cholera, typhoid and dysentery. Organic wastes -- sewage, food-processing effluent, agricultural runoff -- are biodegradable, but their bacterial decomposition consumes large amounts of dissolved oxygen (raising the Biochemical Oxygen Demand, BOD); once oxygen is depleted, fish and other aquatic life suffocate, and the resulting excess of nutrients can also trigger eutrophication (explosive algal growth that further starves the water of oxygen when it decays). Chemical wastes from industrial effluents -- heavy metals, pesticides, synthetic detergents, acids and alkalis -- are …
Microbiological (Pathogens)
Microbiological (pathogen) pollution. Disease-causing microorganisms -- bacteria, viruses and protozoa -- are among the most serious water pollutants. They come from domestic sewage and animal excreta. Fish and shellfish can become contaminated, and people who eat them can become ill; some serious diseases, such as polio and cholera, are water-borne diseases. Human excreta contain bacteria such as *Escherichia …
Organic Wastes
Organic wastes. Organic matter such as leaves, grass and trash can also pollute water, and water pollution is caused by excessive phytoplankton growth within water bodies too. Micro-organisms present in water decompose this organic matter, and in doing so, consume the dissolved oxygen in the water -- the mechanism behind the three related terms de …
Chemical Wastes
Chemical wastes. A whole variety of chemicals from industries, such as metals and solvents, are poisonous to fish and other aquatic life. Some toxic pesticides can accumulate in fish and shellfish and poison the people who eat them. Detergents and oils float on water and spoil water bodies; acids from mine drainage and salts from various sources can also contaminate water sources.
Harmful effects of chemical water pollutants:
- Cadmium and mercury can cause kidney damage. …
Worked out. Three effects listed in the book: (1) Cadmium and mercury can cause kidney damage. (2) Lead poisoning can lead to severe damage of kidneys, liver and brain, and also affects the central nervous system. (3) Polychlorinated biphenyls (PCBs) cause skin diseases and are carcinogenic in nature. …