--- title: "Water pollution, pollutants and adverse effects" subject: "Engineering Chemistry" chapter: 3 key: "semester_2/engineering_chemistry:water-pollutants-effects" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/water-pollutants-effects site: BCT Engineering --- # Water pollution, pollutants and adverse effects Engineering Chemistry · Chapter 3: Environmental Chemistry - Asked in: 2071 Bhadra, 1+2+2 marks - Video: [What Is Water Pollution | Environmental Chemistry | Chemistry | FuseSchool](https://www.youtube.com/watch?v=Zk1J2EW-nmQ) — FuseSchool - Global Education - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/water-pollutants-effects - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-3 ## Question What do you mean by water pollution? What are the major water pollutants, mention their adverse effects. ## Short answer Water pollution is contamination making water unfit for use. Major pollutants include organic sewage, inorganic heavy metals and nitrates, biological pathogens, and suspended solids. Adverse effects are waterborne diseases, Minamata disease (Hg), arsenicosis, eutrophication causing oxygen depletion and fish kills, and biomagnification. ## Answer **Water pollution** is the contamination of water by harmful substances so that it becomes unfit for drinking, agriculture, industry or aquatic life. #### Major water pollutants | Type | Pollutants | Source | |---|---|---| | Organic | Sewage, detergents, pesticides, oil, phenols, food waste | Households, farms, industries | | Inorganic | Heavy metals (Pb, Hg, Cd, As), nitrates, phosphates, acids, alkalis, salts | Industries, mines, fertilisers | | Biological | Bacteria, viruses, protozoa, worms | Sewage, animal waste | | Physical | Suspended solids, heat, radioactive material | Erosion, power plants | #### Adverse effects - **Health:** waterborne diseases (cholera, typhoid, dysentery, hepatitis, diarrhoea); Hg causes Minamata disease, Cd causes itai-itai disease, As causes arsenicosis (found in groundwater of the Terai), Pb damages the brain; nitrate in water causes blue-baby syndrome. - **Eutrophication:** excess nitrate and phosphate cause algal blooms; when the algae die, their decay uses up dissolved oxygen (high BOD, low DO) and fish die. - **Bioaccumulation and biomagnification** of pesticides and metals in the food chain. - Bad taste, smell and colour; water is unfit for drinking, irrigation and industry. - Thermal pollution reduces oxygen solubility and disturbs aquatic life. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is water pollution? A. Increase of dissolved oxygen B. Cooling of water by shade C. Contamination of water by harmful substances so it is unfit for drinking, agriculture, industry or aquatic life D. Natural flow of rivers Answer: C. Pollution makes water unfit for use. (Key point: Definition) 2. How does excess nitrate and phosphate in a lake kill fish? A. They make the water too alkaline for fish gills B. They directly poison fish with nitrate crystals C. They raise dissolved oxygen so much that fish burst D. They cause algal bloom; on decay the algae use up dissolved oxygen (high BOD, low DO) Answer: D. Nutrients cause algal bloom; decay of the algae consumes dissolved oxygen, so fish suffocate. (Key point: Eutrophication) 3. Which pairing of pollutant and disease is correct? A. Hg - Minamata disease; Cd - itai-itai disease B. Hg - itai-itai disease; Cd - Minamata disease C. As - Minamata disease; Pb - arsenicosis D. Cd - blue-baby syndrome; Hg - arsenicosis Answer: A. Mercury causes Minamata disease and cadmium causes itai-itai disease; arsenic causes arsenicosis and nitrate causes blue-baby syndrome. (Key point: Metal diseases) 4. What is the danger of pesticides and metals in the food chain? A. They are diluted at each level so are harmless to top consumers B. They bioaccumulate and are biomagnified, reaching higher concentrations at higher levels C. They are broken down completely by plants D. They only affect aquatic plants Answer: B. Persistent pollutants accumulate and become more concentrated at higher trophic levels. 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