Question

Mention the causes of Water Pollution.

Hint:

For full marks, write point + non-point sources and three key mechanisms: (i) BOD rise $\Rightarrow$ DO depletion, (ii) nutrients $\Rightarrow$ eutrophication/algal blooms, (iii) toxics (metals, pesticides, pharmaceuticals) $\Rightarrow$ bioaccumulation and health hazards. Add thermal pollution and plastics for a contemporary touch.

Answer 1

Meaning
Water pollution is the undesirable change in the physical, chemical or biological quality of water that makes it unfit for intended use (drinking, irrigation, industry, aquatic life). It occurs when the rate of contaminant input exceeds the water body's assimilative capacity $\Rightarrow$ dissolved oxygen falls, toxicity rises, biodiversity declines.
How examiners expect you to organise the causes
Classify by source and by nature:
(a) Point sources (identifiable outlets: sewers, factory pipes) and Non-point sources (diffuse runoff from fields, towns).
(b) Physical (heat, silt), chemical (nutrients, metals, salts, oils, acids/alkalis), biological (pathogens).
Major causes with mechanisms, typical examples and impacts
1) Domestic sewage and wastewater discharge
High BOD/COD from organic matter, detergents, oils, food waste and microplastics $\Rightarrow$ oxygen depletion, foul odour, fish kills. Pathogens from human and animal waste spread diseases (cholera, typhoid, hepatitis). Septic tank leakage contaminates groundwater with nitrates.
2) Industrial effluents
Tanneries (Cr), electroplating (Cr, Ni, Cd), textile dyeing (azo dyes), pulp and paper (chlorinated organics), fertilizer and pesticide units (ammonia, phosphates), refineries (hydrocarbons), pharmaceutical units (antibiotics) $\Rightarrow$ acute and chronic toxicity, colour, foam, mutagenicity, antimicrobial resistance selection. Many effluents are acidic/alkaline, altering pH and solubility of metals.
3) Agricultural runoff
Fertilizers add nitrates and phosphates $\Rightarrow$ eutrophication and harmful algal blooms; decay of algae raises BOD and can produce toxins. Pesticides and herbicides persist and bioaccumulate; run-off peaks during rains from fields, tea/coffee estates, horticulture. Irrigation return flows increase salinity and sodicity in canals and tanks.
4) Oil pollution
Spills from tankers, pipelines, refineries, ship breaking and garages. Thin oil films reduce reaeration and sunlight penetration $\Rightarrow$damage to plankton, birds and mangroves; hydrocarbons can be carcinogenic.
5) Thermal pollution
Hot water released from power plants/industrial cooling increases temperature $\Rightarrow$ lower oxygen solubility, altered metabolism and reproductive cycles in fish; thermal shocks lead to mortality.
6) Solid waste, plastics and microplastics
Littering and dumping in drains and rivers; plastics fragment to micro/nanoplastics ingested by fish and enter food chains; plastics carry adsorbed POPs and metals on their surfaces.
7) Siltation and erosion
Deforestation, construction and sand mining increase suspended solids $\Rightarrow$ turbidity blocks light, clogs gills, smothers benthic eggs and corals; reservoirs lose capacity.
8) Mining and acid mine drainage
Oxidation of sulphide ores makes acidic water rich in Fe, Al, Mn and sulphate; mobilises heavy metals $\Rightarrow$ loss of aquatic life and corrosion of infrastructure.
9) Groundwater contamination and leachates
Leachate from landfills, ash ponds and open dumps; percolation of nitrates, chlorides, pesticides. Geogenic contaminants such as arsenic and fluoride also degrade potable groundwater. Seawater intrusion due to over-pumping salinises coastal aquifers.
10) Pharmaceuticals, hormones and personal-care products
Excreted drugs (analgesics, antibiotics), endocrine disruptors (synthetic hormones, phthalates) pass through conventional treatment $\Rightarrow$ feminisation of fish, behavioural and reproductive effects.
11) Radioactive and hazardous waste
From hospitals, research labs and industry $\Rightarrow$ persistent, long-term ecological and health risks.
12) Detergents and cleaning agents
Surfactants and (where still used) phosphate builders cause foaming and nutrient enrichment; quaternary ammonium compounds can be toxic to aquatic life.
13) Shipping, aquaculture and invasive species
Ballast water releases non-native organisms; antifouling paints release biocides; intensive aquaculture adds antibiotics, feed wastes and fecal matter.
14) Religious and cultural activities, tourism and boating
Immersion of painted idols, garlands, ashes; fuel leaks from boats; crowding near ghats increases litter and sewage load.
Bottom line for answers
State categories and give at least one mechanism and impact for each; link nutrient input $\Rightarrow$ eutrophication, organic load $\Rightarrow$w BOD rise and DO fall, toxicants $\Rightarrow$ bioaccumulation/biomagnification, heat $\Rightarrow$ reduced oxygen and stress.