Causes of Water Pollution

Water pollution occurs not only because pollutants exist but because human activities add them at a scale that natural systems cannot handle. Let us analyse the major causes one by one.

1. Industrial Wastes

Industries are one of the largest contributors to water pollution. Think of them as “point sources” continuously releasing wastewater loaded with harmful chemicals.

Which industries?

• Petroleum refineries
• Paper mills
• Metal extraction and processing units
• Chemical manufacturing industries

These often discharge Toxic Heavy Metals:

Heavy metals = Elements with density > 5 g/cm³
Examples: Mercury, Cadmium, Copper, Lead, Arsenic

These metals do not degrade biologically. They accumulate in water, soil, and eventually the human body.

Heavy Metals in Surface Water (As per Central Water Commission)

India’s surface water reveals a concerning pattern:

Most common contaminant:

• Iron (widespread presence)

Other major contaminants:

• Lead, Nickel, Chromium, Cadmium, Copper

Seasonal Variation (Very important)

During Monsoon:

Metals exceeding tolerance limits:
→ Iron
→ Lead
→ Chromium
→ Copper

Reason: Runoff + soil erosion + disturbed sediments.

During Non-Monsoon:

Common metals:
→ Lead
→ Cadmium
→ Nickel
→ Chromium
→ Copper

Reason: Greater industrial discharge impact due to lower dilution.

Primary Sources of Heavy Metal Pollution

• Mining
• Plating and surface finishing industries
• Metal extraction processes

Health Impacts

Long-term exposure may lead to conditions resembling:

• Alzheimer’s disease
• Parkinson’s disease
• Muscular dystrophy
• Multiple sclerosis

These arise due to neurological and muscular degeneration caused by bioaccumulation of metals.

2. Thermal and Radiation Pollution

Industries release not only chemical pollutants, but also heat and radioactive substances under certain conditions.

(A) Thermal Pollution

Many industries use water as a coolant:

• Thermal power plants
• Nuclear power plants
• Chemical industries

When hot water is discharged back into rivers or oceans, the temperature rises by 5–15°C.

Why is this harmful?

1. Dissolved Oxygen (DO) decreases as temperature increases.
   → Aquatic life faces oxygen stress.
2. Aquatic species are adapted to steady temperatures.
   → Sudden temperature rise → shock → mass fish deaths.

(B) Radiation Pollution

This type of pollution is rare but extremely dangerous.

Sources:

• Nuclear accidents near water bodies
• Natural disasters (tsunamis, earthquakes) causing leakage
• Example: Fukushima Daiichi nuclear disaster

Impacts of Radiation Exposure:

Radiation damages DNA, causing:
➡️Mutations
➡️Cancerous cell development if mutations are not repaired

Examples of radioactive threats:

• Radioactive iodine (I-131) → absorbed by thyroid gland → risk of thyroid cancer
• Radioactive radon in air/water → lung cancer
• Uranium in water → kidney cancer

3. Mining

Mining is a major source of chemical, heavy metal, and sediment pollution.

Both open-pit and underground mining use large quantities of water for:
➡️Raw material processing
➡️Mine cooling
➡️Metal extraction

They involve chemicals like:

• Cyanide
• Sulphuric acid
• Mercury

These can easily contaminate groundwater and surface water.

(A) Sedimentation and Chemical Runoff

Mining disturbs huge volumes of Soil and Rock.

Erosion carries Sediments and Toxic chemicals → into rivers, streams, lakes → reducing DO, increasing turbidity, harming aquatic life.

(B) Acid Rock Drainage (ARD)

ARD is natural, occurring when sulphides in rocks react with water, producing sulphuric acid.

This acid:

• Accelerates rock weathering
• Leaches metals/minerals into water

(C) Acid Mine Drainage (AMD)

AMD is the industrial-scale, intensified version of ARD.

Occurs when:

• Huge volumes of sulphide-rich rock are excavated (open-pit or underground mining)

AMD creates extremely acidic water, which has two major outcomes:

Bacterial Acceleration

A bacterium called Thiobacillus ferrooxidans thrives in low pH (1.5–2.0).

It accelerates:
➡️Oxidation
➡️Acidification
➡️Release of trace metals

This becomes a self-reinforcing cycle.

(D) Heavy Metal Mobilization

Metals like:
→ Arsenic
→ Cobalt
→ Copper
→ Cadmium
→ Lead
→ Silver
→ Zinc
…become highly mobile when exposed to low pH conditions created by AMD.

Even though these metals can leach at neutral pH, the process is dramatically accelerated under acidic conditions.

4. Groundwater & Drinking Water Contamination

Groundwater is one of India’s most vital water sources—especially for rural drinking water. But today, it faces serious contamination from industrial waste, agricultural runoff, and natural geochemical processes.

Let’s understand this:

Why Is India’s Groundwater Getting Contaminated?

Groundwater is threatened primarily due to:

• Seepage from industrial wastes
• Leakage of municipal sewage
• Agricultural runoff carrying fertilizers and pesticides

As a result, the following pollutants frequently enter aquifers:

• Fluorides
• Uranium
• Heavy metals
• Nitrates and phosphates

These contaminants make groundwater unsafe for drinking even before treatment.

Drinking Water Issues in Rural India

Many rural habitations report poor water quality.

Most common contaminants in rural drinking water:

1. Iron – the most widespread
2. Salinity – highest in Rajasthan
3. Arsenic – worst in West Bengal and Assam
4. Fluoride

These pollutants vary by region depending on geology, groundwater depth, and land use.

Nitrates — A Major Chemical Threat

Nitrates enter water mainly from:

• Fertilizers (urea, ammonium nitrate)
• Sewage
• Animal waste

Health Impact: Blue Baby Syndrome

Excess nitrate reacts with haemoglobin to form methaemoglobin, which cannot carry oxygen.

This condition is:
➡ Methemoglobinemia (popularly called Blue Baby Syndrome)

Symptoms:

• Breathlessness
• Blue coloration of skin
• Poor oxygen supply to tissues

Nitrates may also:

• Form carcinogenic compounds
• Accelerate eutrophication in water bodies

Trace Metals

Common trace metals in groundwater include:
→ Lead
→ Mercury
→ Cadmium
→ Copper
→ Chromium
→ Nickel

These are potentially carcinogenic and can cause long-term organ damage.

Arsenic Contamination

Arsenic is one of the most dangerous pollutants in groundwater.

Key features of arsenic:

• Tasteless
• Odourless
• Highly poisonous
• Carcinogenic

Arsenic occurs naturally in some rocks, but is also released by:

• Mining
• Manufacturing
• Fly ash disposal from thermal power plants

Geographical prevalence:

• Highest contamination in Ganges Delta (India & Bangladesh)
• High levels also found in USA, China, Mexico

Major health effects:

1. Black Foot Disease
   • A type of peripheral vascular disease
   • Causes severe damage to blood vessels → gangrene
2. Arsenicosis
   • Due to long-term ingestion/inhalation
   • Causes:
     • Melanosis (dark spots on skin)
     • Keratosis (thickened palms & soles)
     • Lung cancer
     • Skin cancer
     • Chronic diarrhoea

Arsenic poisoning is a classic example of how a natural element becomes lethal when mobilized in high concentration.

Fluoride Contamination

Fluoride occurs naturally in rocks and aquifers, especially in arid regions.

Health impact: Fluorosis

Excess fluoride intake leads to:

• Dental fluorosis (tooth deformity)
• Skeletal fluorosis (hardening of bones, joint stiffness)
• Neuromuscular disorders
• Gastrointestinal issues

A classic symptom is:
➡ Knock-Knee Syndrome
(legs bend outward from the knees due to bone weakening)

Fluorosis is widespread across Indian states like Rajasthan, Andhra Pradesh, Telangana, and Karnataka.

Uranium Contamination

Uranium is weakly radioactive, but chemically harmful.

Key facts:

• Physical half-life (U-238) ≈ 4.5 billion years
• Biological half-life ≈ 15 days

What this means:
➡️Physical half-life: The time it takes for half of uranium-238 atoms to decay radioactively (≈ 4.5 billion years).
➡️Biological half-life: The time it takes for the human body to eliminate half of the absorbed uranium through biological processes (≈ 15 days).

WHO guideline for uranium in drinking water:
➡ 30 micrograms per litre (µg/L)

Where does uranium come from in India?

• Rajasthan & NW India: from alluvial aquifers
• Telangana, Karnataka, parts of AP: from granite and crystalline rocks

How groundwater extraction increases uranium levels?

Over-extraction lowers the water table → exposes uranium-bearing minerals to air → promotes oxidation → uranium dissolves into groundwater.

Health effects:

• Kidney toxicity
• Linked to chronic kidney disease (CKD) cases in Srikakulam district, Andhra Pradesh

The Andhra Pradesh government even ordered an inquiry into contamination around UCIL (Uranium Corporation of India Limited) in Kadapa.

Guidelines in India for Radioactive Substances

Indian Standard IS 10500:2012 regulates drinking water quality.

Key points:

• Specifies limits for alpha and beta emitters
• Applies to all radioactive elements, including uranium
• BIS is updating standards to include a specific limit for uranium:
  ➝ 0.03 mg/L (same as WHO guideline)

Radioactive Radon in Groundwater

Recent studies in Bengaluru show alarming levels of radon in groundwater—up to 50–100 times the permissible limit of 11.1 Bq/L.

Sources of radon:

• Radioactive granite rocks
• Uranium decay → radium → radon
• Minerals like:
  • Pitchblende
  • Zircon
  • Monazite

Health impact:

• Radon → lung cancer
• Uranium → kidney cancer

Freshwater Salinization Syndrome (FSS)

FSS refers to increasing salt concentration in freshwater systems due to natural and human factors.

Natural causes:

• Rock weathering
• Naturally saline groundwater

Anthropogenic causes:

1. Oil & gas extraction
2. Road salts for de-icing
   (salt lowers freezing point of ice)
3. Accelerated weathering of rocks and soils
4. Sea-level rise → saltwater intrusion
   (major threat for coastal aquifers)

FSS alters water chemistry, affects aquatic life, and makes water unfit for consumption.

5. Sewage Water

Sewage is one of the biggest contributors to water pollution in India.

What does sewage contain?

• Human & animal excreta
• Food residues
• Detergents and cleaning agents
• Pathogenic microbes (especially in domestic + hospital sewage)

When such untreated wastewater enters rivers or lakes, it introduces organic waste, disease-causing organisms, and excess nutrients, degrading water quality.

Ammonia Pollution in Sewage

Ammonia is:

• A colourless gas with a strong smell
• Naturally present in air, water, soil, animals and humans

Why is ammonia common in wastewater?

• Human body produces ammonia when proteins break down
• Converts ammonia → urea (excreted in urine)
• Also present in cleaning agents and ammonium nitrate fertilizers

Ammonia in water treatment

For 70+ years, municipalities have used ammonia to:

• React with chlorine → form chloramines
• This prolongs disinfection effectiveness
• Reduces cancer-causing by-products of chlorination
• But chloramines create bad taste in water

Safety limits

• BIS acceptable limit: 0.5 ppm
• >1 ppm: toxic to fish
• ≥1 ppm long-term exposure: harmful to humans

6. Agricultural Sources

Agriculture contributes heavily to chemical water pollution through fertilizers, pesticides, and animal waste.

Agricultural runoff typically contains:

• Nitrates
• Phosphates
• Potassium
• Ammonia
• Organic compounds
• Toxic metal ions

These reach:

• Groundwater through leaching
• Surface water through runoff

Fertilizers

Contain major plant nutrients:
➡ Nitrogen, Phosphorus, Potassium (NPK)

Only 33% of nitrogen from fertilizers is actually used by crops.
The remaining 67% stays in soil or leaches into water → causing nitrogen pollution.

Pesticides

The major groups include:

(A) Chlorinated hydrocarbons (CHCs)

• DDT
• Endosulfan
  → Highly persistent, long environmental life

(B) Organophosphates

→ Affect nervous system

(C) Metallic salts, carbonates

Most pesticides are non-degradable, meaning they bioaccumulate and biomagnify through the food chain.

Animal waste runoff

Wastes from:
→ Poultry
→ Piggeries
→ Slaughterhouse
…carry organic pollutants and pathogens into water.

7. Invasive Aquatic Species

Some species multiply uncontrollably in nutrient-rich waters (often due to pollution), damaging ecosystems.

Water Hyacinth

An aggressive invasive plant from the Amazon.

Nicknames:

• Terror of Bengal (India)
• German Weed (Bangladesh)
• Florida Devil (South Africa)
• Japanese Trouble (Sri Lanka)

Why is it harmful?

• Thrives in eutrophic, nutrient-rich waters
• Forms thick mats → block sunlight
• Consumes oxygen → kills fish
• Stagnates water → mosquito breeding
• Chokes waterways & irrigation channels

Forked Fanwort (in Kerala)

• Submerged perennial plant
• Invasive, from Central and South America
• Requires high oxygen → reduces availability for native species
• Heavy growth “paints” water bodies pink
• Disrupts freshwater biodiversity
  
  

8. Pollution in River Ganga

Ganga suffers from multiple pollution sources across its entire length.

Major urban + industrial hotspots:

• Haridwar
• Kannauj
• Kanpur
• Allahabad
• Varanasi
• Patna
• Kolkata

Industries contributing most to pollution:

• Tanneries
• Sugar & distilleries
• Pulp & paper mills

Key pollutants

(A) Faecal coliform bacteria

Present throughout the river length → indicates untreated sewage discharge.

(B) BOD (Biochemical Oxygen Demand)

Extremely high between Kannauj → Tarighat, indicating heavy organic pollution.

(C) Low flow due to canal diversion

Upper & Lower Ganga canals divert large volumes of water.
Low flow = very little dilution → even treated sewage remains harmful.

Microplastics in Ganga

Detected types include:

• Ethylene-vinyl → packaging (food, cosmetics, drugs)
• Polyacetylene → electronics (doping agent)
• Polypropylene → packaging, sheets, fabrics, ropes
• Persistent Inorganic Polymers (PIP) → footwear, baby bottle nipples
• Polyamide (Nylon) → clothing, industrial uses

Microplastics persist for centuries and enter the food chain.

9. Marine Pollution: Oil Spills & Plastics

Marine pollution occurs when chemicals, sewage, plastics, and oil enter the oceans.

Toxins stick to small particles → consumed by plankton and benthos → move up the food chain → finally reach humans (through seafood).

Oil Spills

Causes:

• Marine transport leaks
• Underground tank leakage
• Offshore drilling accidents

Recent Oil Spill Incidents

1. 2023 – Poole Harbour Spill (UK)
A pipeline leak released ~28,000 litres of oily wastewater into Poole Harbour, a highly sensitive marine ecosystem.

2. 2021 – Peru (Repsol) Oil Spill
Around 6,000 barrels of crude oil spilled near Lima after the Tonga volcanic eruption, causing Peru’s worst coastal ecological disaster.

3. 2021 – Israel Mediterranean Oil Spill
A mysterious offshore leak caused tar pollution along 160 km of Israel’s coastline, impacting beaches and marine life.

4. 2020 – Russia Norilsk Arctic Diesel Spill
Over 21,000 tonnes of diesel leaked into Arctic rivers after a storage tank collapse, declared Russia’s worst-ever inland spill.

Impact on marine life

Oil forms a thin film on the water surface → blocks sunlight → reduces oxygen exchange.

Effects:

• Fish, shellfish, plankton die within hours
• Birds & mammals die after consuming contaminated prey
• Disturbs metabolic and reproductive systems

Cleanup methods:

• Bregoli (paper industry by-product, like sawdust)
• Oil Zapper (microbial oil degrader)
• Other microorganisms

Marine Plastic Pollution

A global crisis with severe ecological and economic consequences.

Key facts:

• Causes $13 billion economic loss annually
• At current trends, plastics may outweigh fish by 2050
• Even found in the deepest ocean trench (Challenger Deep)
• Present in sea salt and microplastics detected even in the Arctic

Impact on life:

• Ingestion, suffocation, entanglement
• Wildlife (seabirds, whales, turtles) mistake plastic for food → stomach fills with plastic → death by starvation
• Chemicals from plastics interfere with:
  • Growth
  • Photosynthesis
  • Oxygen production in Prochlorococcus (most abundant photosynthetic organism in oceans)

This has implications for global oxygen levels.