Water Pollution — Revision Notes

⚡ 30-Second Revision

Water Pollution: — Contamination of water bodies by harmful substances.
Point Sources: — Identifiable, localized discharge points (e.g., factory pipes).
Non-Point Sources: — Diffuse, widespread sources (e.g., agricultural runoff).
Pollutants: — Pathogens, organic waste, heavy metals ($Hg, Pb, Cd$), nutrients ($NO_3^-, PO_4^{3-}$), sediments, thermal.
Dissolved Oxygen (DO): — Oxygen in water, essential for aquatic life. Clean water: $8-10,\text{ppm}$. Polluted water: $<4-5,\text{ppm}$.
Biochemical Oxygen Demand (BOD): — Oxygen consumed by microbes for organic decomposition. High BOD = high organic pollution. Clean water: $<5,\text{ppm}$. Highly polluted: $>17,\text{ppm}$.
Chemical Oxygen Demand (COD): — Oxygen for chemical oxidation of all organic/inorganic matter. Usually $>$ BOD.
Eutrophication: — Nutrient enrichment ($NO_3^-, PO_4^{3-}$) $ightarrow$ algal blooms $ightarrow$ DO depletion.
Biomagnification: — Increasing pollutant concentration up the food chain (e.g., DDT, Mercury).
Minamata Disease: — Caused by Mercury ($Hg$) poisoning.
Itai-Itai Disease: — Caused by Cadmium ($Cd$) poisoning.

2-Minute Revision

Water pollution involves the degradation of water quality by introducing harmful substances. Sources are either point sources (identifiable, like factory pipes) or non-point sources (diffuse, like agricultural runoff).

Key pollutants include pathogens (disease-causing microbes from sewage), organic waste (which consumes oxygen during decomposition, measured by BOD), heavy metals (like mercury causing Minamata disease, cadmium causing Itai-Itai disease, which biomagnify), and excess nutrients (nitrates and phosphates from fertilizers/sewage).

These nutrients lead to eutrophication, where algal blooms deplete Dissolved Oxygen (DO), harming aquatic life. Clean water has high DO ($8-10,\text{ppm}$) and low BOD ($<5,\text{ppm}$). Polluted water shows the opposite.

Chemical Oxygen Demand (COD) measures total oxidizable matter. Understanding these parameters and the specific impacts of pollutants is crucial for NEET.

5-Minute Revision

Water pollution, a critical environmental issue, is the contamination of water bodies by substances that render them unfit for use. It originates from two main types of sources: point sources, which are easily identifiable and localized (e.g., industrial discharge pipes, sewage treatment plant outfalls), and non-point sources, which are diffuse and widespread (e.g., agricultural runoff carrying fertilizers and pesticides, urban stormwater runoff).

Key pollutants include:

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Pathogens: — Disease-causing microorganisms (bacteria, viruses) from untreated sewage, leading to waterborne diseases.
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Organic Pollutants: — Biodegradable organic matter (human/animal waste) consumes Dissolved Oxygen (DO) during decomposition by microbes. This oxygen demand is quantified by Biochemical Oxygen Demand (BOD). Clean water has high DO ($8-10,\text{ppm}$) and low BOD ($<5,\text{ppm}$), while polluted water has low DO and high BOD ($>17,\text{ppm}$ for highly polluted). Non-biodegradable organic pollutants like pesticides (DDT) and PCBs are persistent and undergo biomagnification up the food chain.
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Inorganic Pollutants:

* Heavy Metals: Toxic metals like mercury ($Hg$), lead ($Pb$), cadmium ($Cd$), and arsenic ($As$) from industrial effluents. Mercury causes Minamata disease, and cadmium causes Itai-Itai disease.

They are non-biodegradable and bioaccumulate. * Nutrients: Nitrates ($NO_3^-$) and phosphates ($PO_4^{3-}$), primarily from agricultural runoff and detergents, cause eutrophication. This process leads to rapid algal growth (algal blooms), which block sunlight, die, and their decomposition consumes vast amounts of DO, creating 'dead zones'.

* Acids/Alkalis: Alter pH, harming aquatic life.

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Thermal Pollution: — Discharge of heated water (e.g., from power plants) reduces DO solubility, stressing aquatic organisms.

Chemical Oxygen Demand (COD) measures the total oxygen required for chemical oxidation of all organic and inorganic matter, providing a quicker assessment than BOD. Effective control involves proper sewage and industrial waste treatment, sustainable agricultural practices, and public awareness.

Prelims Revision Notes

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Definition: — Water pollution is the contamination of water bodies by harmful substances, making it unsuitable for use.
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Sources:

* Point Sources: Specific, identifiable locations (e.g., industrial discharge pipes, sewage outfalls). Easier to regulate. * Non-Point Sources: Diffuse, widespread areas (e.g., agricultural runoff, urban stormwater, atmospheric deposition). Difficult to control.

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Key Pollutants and their Effects:

* Pathogens: Bacteria (*E. coli*, *Salmonella*), viruses (Hepatitis A), protozoa (*Giardia*) from untreated sewage. Cause waterborne diseases (cholera, typhoid). * Organic Waste (Biodegradable): Human/animal excreta, food waste.

Decomposed by microorganisms, consuming Dissolved Oxygen (DO). * BOD (Biochemical Oxygen Demand): Amount of oxygen consumed by microbes to decompose organic matter (typically 5 days at $20^circ C$).

* Clean water: BOD $<5,\text{ppm}$. * Moderately polluted: BOD $5-10,\text{ppm}$. * Highly polluted: BOD $>17,\text{ppm}$. * Non-Biodegradable Organic Pollutants: Pesticides (DDT), PCBs, plastics.

Persistent, undergo biomagnification (increasing concentration up food chain). * Heavy Metals: Toxic elements ($Hg, Pb, Cd, As, Cr$) from industrial effluents (mining, electroplating). * **Mercury ($Hg$):** Causes Minamata disease (neurological).

* **Cadmium ($Cd$):** Causes Itai-Itai disease (bone/kidney damage). * Non-biodegradable, bioaccumulate in tissues. * Nutrients: Nitrates ($NO_3^-$) and Phosphates ($PO_4^{3-}$), from fertilizers, detergents, sewage.

* Cause Eutrophication: Nutrient enrichment $ightarrow$ algal blooms $ightarrow$ reduced light $ightarrow$ death of aquatic plants/algae $ightarrow$ decomposition by bacteria $ightarrow$ severe DO depletion $ightarrow$ fish kills ('dead zones').

* Thermal Pollution: Increase in water temperature (e.g., from power plant cooling water). * Reduces solubility of gases, especially DO, stressing aquatic life.

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Water Quality Parameters:

* DO (Dissolved Oxygen): Essential for aerobic aquatic life. Clean water: $8-10,\text{ppm}$. Low DO indicates pollution. * BOD (Biochemical Oxygen Demand): Indicator of organic pollution. Higher BOD = more pollution. * COD (Chemical Oxygen Demand): Measures total oxidizable organic and inorganic matter. Generally higher than BOD. * pH: Most aquatic life thrives in $6.5-8.5$. Extreme pH is toxic. * Coliform Count: Indicates fecal contamination.

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Control Strategies: — Sewage treatment (primary, secondary, tertiary), industrial effluent treatment, sustainable agriculture, urban runoff management, legislation.

Vyyuha Quick Recall

To remember the key water quality parameters and their relation to pollution: BODy DOesn't like COD.

BOD — (Biochemical Oxygen Demand): High BOD = Bad (polluted water, low DO).
DO — (Dissolved Oxygen): High DO = Good (clean water, low BOD).
COD — (Chemical Oxygen Demand): Comprehensive measure, always higher than BOD, also indicates pollution.