💧 Chapter 05 · Topic 02 · Environmental Pollution

Water Pollution — BOD, Eutrophication & Ganga

BOD, COD, dissolved oxygen, eutrophication, thermal pollution, heavy metal diseases, Ganga pollution and Namami Gange — complete UPSC & PSC notes.

💧 Key Water Quality Parameters

Parameter	Full Form	What it Measures	Key Values
BOD	Biochemical Oxygen Demand	Oxygen needed by microbes to decompose organic matter (5 days, 20°C)	Clean water <5 mg/L; Sewage 200–300 mg/L
COD	Chemical Oxygen Demand	Total oxygen needed to oxidise all chemical substances (biodegradable + non-biodegradable)	Always higher than BOD
DO	Dissolved Oxygen	Actual oxygen dissolved in water; essential for aquatic life	Healthy >6 mg/L; Fish die <4 mg/L

⭐ Exam Tip: Higher BOD = more polluted water. Higher DO = cleaner water. BOD and DO are inversely related — as organic pollution increases, microbes consume DO, reducing it. This is the basis of the Oxygen Sag Curve — DO drops downstream of a pollution source, then recovers.

💧 Eutrophication

Eutrophication = enrichment of water body with nutrients (mainly nitrogen and phosphorus), leading to excessive algal growth
Process: Nutrient input → algal bloom → algae block sunlight → submerged plants die → algae die → bacterial decomposition consumes all DO → fish and aquatic life die → “dead zone”
Cultural eutrophication — caused by human activities (agricultural runoff, sewage discharge)
Natural eutrophication — slow, natural process over thousands of years
Affected water bodies in India: Chilika Lake, Dal Lake, Hussain Sagar, Powai Lake

📌 Algal Bloom: Rapid growth of algae on water surface. Some algal blooms are toxic (Harmful Algal Blooms — HABs) — produce toxins that kill fish and are dangerous to humans. Blue-green algae (cyanobacteria) blooms are common in eutrophic water bodies.

💧 Sources of Water Pollution

Source	Pollutants	Effects
Industrial effluents	Heavy metals (Hg, Pb, Cd, As), acids, dyes, cyanide	Bioaccumulation, cancer, neurological damage
Agricultural runoff	Pesticides, fertilisers (N, P), herbicides	Eutrophication, groundwater contamination, blue baby syndrome
Domestic sewage	Pathogens, organic matter, detergents	Waterborne diseases, high BOD, eutrophication
Mining	Acid mine drainage, heavy metals, sediment	Acidification, heavy metal contamination
Thermal pollution	Hot water from power plants	Reduces DO, disrupts breeding, kills aquatic life
Oil spills	Petroleum hydrocarbons	Kills seabirds, fish; coats marine organisms
Radioactive waste	Radioactive isotopes	Cancer, genetic mutations in aquatic organisms

💧 Heavy Metal Pollution — Key Diseases

Metal	Disease	Location	Source	Effects
Mercury (Hg)	Minamata disease	Minamata, Japan (1950s)	Chemical factory discharge	Neurological damage, paralysis, death
Cadmium (Cd)	Itai-Itai disease	Toyama, Japan (1950s)	Mining waste in rice fields	Bone pain, kidney damage, fractures
Arsenic (As)	Arsenicosis	West Bengal, Bangladesh	Groundwater contamination	Skin lesions, cancer, keratosis
Lead (Pb)	Lead poisoning	Worldwide	Old pipes, batteries, paint	Neurological damage, especially in children
Fluoride (F)	Fluorosis	Rajasthan, AP, Telangana	Groundwater	Dental and skeletal fluorosis
Nitrates (NO₃)	Blue Baby Syndrome	Agricultural areas	Fertiliser runoff	Methaemoglobinaemia in infants

💧 Biomagnification & Bioaccumulation

Bioaccumulation — gradual accumulation of a toxic substance in a single organism over its lifetime
Biomagnification — progressive increase in concentration of a toxin at each successive trophic level in a food chain
Classic example — DDT: Water (0.000003 ppm) → Plankton (0.04 ppm) → Small fish (0.5 ppm) → Large fish (2 ppm) → Birds (25 ppm)
DDT caused eggshell thinning in birds (bald eagle, peregrine falcon) → population crashes
Persistent pollutants that biomagnify: DDT, PCBs, mercury, dioxins, furans
These are also called POPs (Persistent Organic Pollutants) — regulated by Stockholm Convention

💧 Ganga Pollution

Ganga is the most polluted river in India; flows through 11 states; 500 million people depend on it
Receives untreated sewage from 100+ cities; only ~30% of sewage is treated
Major pollutants: untreated sewage (largest contributor), industrial effluents (tanneries in Kanpur — chromium), religious offerings, cremation ash
Kanpur tanneries discharge chromium — a toxic heavy metal
Ganga declared National River in 2008
Ganga Action Plan (GAP) — launched 1985; largely unsuccessful
Namami Gange Programme — launched 2014; ₹20,000 crore; implementing agency: NMCG (National Mission for Clean Ganga)
Key components of Namami Gange: sewage treatment plants, industrial effluent treatment, ghats development, afforestation, biodiversity conservation

⭐ Ganga Dolphins: The Gangetic River Dolphin (Platanista gangetica) is India’s National Aquatic Animal. It is critically endangered due to Ganga pollution, dams, and fishing nets. It is blind and navigates by echolocation. Project Dolphin was launched in 2020.

💧 Thermal Pollution

Discharge of heated water from thermal and nuclear power plants into water bodies
Warm water holds less dissolved oxygen → stresses aquatic organisms
Accelerates metabolism of aquatic organisms → disrupts breeding cycles
Makes water bodies more susceptible to algal blooms
Solutions: cooling towers, cooling ponds, spray ponds to reduce temperature before discharge

💧 Water Pollution Control

Water (Prevention and Control of Pollution) Act 1974 — establishes CPCB and SPCBs; sets water quality standards
Sewage Treatment Plants (STPs) — treat domestic sewage before discharge
Effluent Treatment Plants (ETPs) — treat industrial effluents
Zero Liquid Discharge (ZLD) — industries must treat and reuse all wastewater; no discharge
Constructed wetlands — natural treatment of wastewater using plants and microorganisms
Jal Jeevan Mission — safe drinking water to all rural households by 2024

✅ Revision Checklist — Water Pollution

✅ BOD = oxygen needed by microbes = higher BOD = more polluted; clean water <5 mg/L
✅ DO = dissolved oxygen = healthy water >6 mg/L; fish die <4 mg/L
✅ Eutrophication = excess N + P → algal bloom → DO depletion → fish die
✅ Minamata disease = mercury poisoning (Japan); Itai-Itai = cadmium (Japan)
✅ Arsenicosis = arsenic in groundwater = West Bengal + Bangladesh
✅ Fluorosis = excess fluoride = dental + skeletal damage = Rajasthan, AP, Telangana
✅ Blue Baby Syndrome = excess nitrates = methaemoglobinaemia in infants
✅ Biomagnification = toxin concentration increases up food chain
✅ DDT = classic biomagnification example = eggshell thinning in birds
✅ Ganga = National River (2008) = most polluted river in India
✅ Namami Gange = 2014 = ₹20,000 crore = NMCG implementing agency
✅ Gangetic Dolphin = National Aquatic Animal = blind = echolocation
✅ Thermal pollution = hot water from power plants = reduces DO
✅ Water Act 1974 = establishes CPCB + SPCBs
✅ ZLD = Zero Liquid Discharge = no industrial wastewater discharge