--- title: "Water pollutants, harmful effects, control measures" subject: "Engineering Chemistry" chapter: 3 key: "semester_2/engineering_chemistry:water-pollutants-effects-measures" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/water-pollutants-effects-measures site: BCT Engineering --- # Water pollutants, harmful effects, control measures Engineering Chemistry · Chapter 3: Environmental Chemistry - Asked in: 2069 Poush, 3+2 marks - Video: [WATER POLLUTION Explained: Causes, Impacts, and Real Solutions | Control Measures & Case Studies..!](https://www.youtube.com/watch?v=KaKr-qCJtqU) — Knowledge Chronicle - 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-measures - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-3 ## Question What are the major water pollutants and their harmful effect? Mention the possible measures to control water pollution. ## Short answer Major water pollutants are organic waste, heavy metals, pathogens, and suspended solids. They cause waterborne diseases, eutrophication, bioaccumulation, and degrade water quality. Control requires sewage treatment, reduced fertilizer use, preventing waste dumping, and strict environmental laws. ## Answer #### 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 | #### Harmful 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. #### Control measures - Treat sewage and industrial effluents before discharge (primary, secondary and tertiary treatment). - Use less fertiliser and pesticide; use organic farming; ban phosphate detergents. - Prevent dumping of solid waste in rivers; build proper sanitation and toilets. - Cool hot water before discharge; recycle and reuse water. - Strict laws (polluter pays), regular monitoring, public awareness and river-cleaning programmes (such as for the Bagmati). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. 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) 2. 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) 3. Which is a key remedy for water pollution from sewage and industry? A. Discharge them directly into rivers so they dilute B. Treat sewage and industrial effluents (primary, secondary, tertiary) before discharge C. Add more phosphate detergents D. Dump solid waste into rivers so it settles Answer: B. Treating effluents before discharge removes pollutants at the source. (Key point: Effluent treatment) 4. Which measures reduce agricultural water pollution? A. Increase fertiliser use to boost crops B. Use more DDT instead of organic methods C. Use less fertiliser and pesticide, organic farming, and ban phosphate detergents D. Irrigate with untreated sewage Answer: C. Cutting nutrient and pesticide inputs reduces runoff pollution and eutrophication. 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