Ch 10: Environmental Chemistry

📋 Types of Environmental Pollution

💨

Air Pollution

Contamination by harmful gases, particulates and chemicals. Greenhouse gases, Smog, Acid Rain, Ozone depletion.

💧

Water Pollution

Contamination by industrial, agricultural and domestic waste. BOD, Eutrophication, heavy metals.

🪨

Soil Pollution

Contamination by pesticides, heavy metals, industrial waste. DDT is a persistent soil pollutant.

🔊

Sound Pollution

Noise can damage hearing; NIOSH’s occupational reference is 85 dBA averaged over 8 hours, not a universal instant-harm threshold

☢️

Radiation / Radioactive Pollution

Pollution caused by radioactive substances and nuclear waste.

⚠️ Exam Trap

DDT = Dichloro Diphenyl Trichloroethane — persistent pollutant (stays in environment)
PCBs = Polychlorinated Biphenyls = carcinogenic industrial pollutant

🌡️ Global Warming & Greenhouse Effect

📘 Greenhouse Effect

Greenhouse gases trap heat in Earth's atmosphere → increases Earth's temperature → Global Warming.

GREENHOUSE GASES:

CO₂

CH₄ (Methane)

N₂O

CFC (Freon)

Water vapour

⚠️ Exam Trap — Greenhouse Gases

CO₂ is the largest contributor among long-lived anthropogenic greenhouse gases; distinguish this from the natural greenhouse effect
Methane’s 100-year GWP is about 27–30× CO₂ in the OP reference; it is not the most potent greenhouse gas known
CFC is both greenhouse gas AND ozone depleter

🌫️ Smog

General Smog

Reducing mixture

Composition: Smoke + Fog + SO₂
Nature: Reducing
Common in industrial areas with coal burning

Photochemical Smog

Oxidative nature

Formed from: Oxides of Nitrogen + Hydrocarbons (in sunlight)
Nature: Oxidative
Important secondary components: O₃, PAN, NO₂ and aldehydes

📘 PAN (Peroxy Acetyl Nitrate)

Key component of photochemical smog. Causes eye irritation and plant damage. Formula: CH₃CO·O₂NO₂

⚠️ Exam Trap — Smog

PAN = peroxyacetyl nitrate; it belongs to the broader peroxyacyl-nitrate family
Photochemical smog = Oxidative; General smog = Reducing
Photochemical-smog components: O₃, PAN, NO₂ and aldehydes

🌧️ Acid Rain

📘 Acid Rain

Rainwater with pH below 5.6. Normal rain has pH 5.6 (slightly acidic due to dissolved CO₂).

Normal Rain pH

5.6

Acid Rain pH

< 5.6

Responsible Gases

SO₂ + NO₂

Responsible gases: SO₂ and NO₂ (from industrial emissions, vehicles)
Damages historic monuments (marble/limestone buildings)
Harms soil, water bodies, forests
Marble cancer = acid rain eroding Taj Mahal

⚠️ Exam Trap — Acid Rain

Acid rain pH = below 5.6 (NOT below 7)
Caused by SO₂ and NO₂ (NOT CO₂)
CO₂ makes normal rain slightly acidic (pH 5.6) but that is NOT acid rain

🌐 Ozone Depletion

📘 Ozone Layer

Present in the Stratosphere. Protects Earth from harmful UV radiation. CFC destroys ozone molecules.

Location: Stratospheric pollution
Main cause: CFC (Chlorofluorocarbon) and Halogens
Freon is a historical trade name for several halocarbon refrigerants, including some CFCs
CFC composition: Compounds of C, Cl and F
CFCs were historically used as refrigerants, propellants, foam-blowing agents and solvents; many uses have been phased out
CFC breakdown releases chlorine radicals that catalytically destroy many ozone molecules before being removed

⚠️ Exam Trap — Ozone

CFC = Chlorofluorocarbon = Freon = depletes ozone
CFCs: historical refrigerants/propellants; many uses phased out
Ozone depletion = Stratospheric pollution (NOT tropospheric)
Ozone hole first discovered over Antarctica
CFC is also a greenhouse gas (dual effect)

💧 Water Pollution — BOD

📘 BOD — Biochemical Oxygen Demand

Amount of oxygen consumed by aerobic bacteria to decompose organic matter in polluted water. Higher BOD = More polluted.

≤2 mg/L

BOD₅: CPCB Class A

≤3 mg/L

BOD₅: CPCB Classes B/C

🌿 Eutrophication

📘 Eutrophication

Process where excess nutrients (nitrates, phosphates from fertilisers) enter water bodies → Algal bloom → Respiration and microbial decomposition of bloom biomass consume dissolved O₂ → Depletion of O₂ in water → Fish and aquatic life die.

Caused by excess nitrates and phosphates (from agricultural runoff, sewage)
→ Algal bloom (rapid growth of algae)
→ Dissolved O₂ depleted
→ Death of aquatic life (fish kill)

⚠️ Exam Trap — Eutrophication

Excess nutrients promote algal blooms; respiration and microbial decomposition of biomass can deplete dissolved O₂ and harm aquatic life

🧪 Drinking-Water Guidance — WHO Values Recorded in OP

Metal	Symbol	Guideline / operational context (mg/L)	Health / acceptability context
Iron	Fe	No WHO health-based guideline value	Mainly taste, colour and staining at typical levels
Manganese	Mn	0.08 mg/L (provisional WHO guideline)	Excess long-term exposure can affect the nervous system
Aluminium	Al	Operational residual targets: ≤0.1 mg/L large supplies; ≤0.2 mg/L small supplies	No formal health-based WHO value; no established causal link to Alzheimer’s disease
Copper	Cu	2 mg/L (WHO guideline)	High concentrations can cause acute gastrointestinal effects
Zinc	Zn	No WHO health-based guideline value	Mainly taste/acceptability; very high intake can cause nausea
Cadmium	Cd	0.003 mg/L (WHO guideline)	Chronic exposure damages kidneys; Itai-Itai association

⚠️ Exam Trap — Metal Limits

Of Mn, Cu and Cd, cadmium has the lowest listed WHO health-based value: 0.003 mg/L. Guideline order is not a universal toxicity ranking.
WHO sets no health-based guideline value for zinc at typical drinking-water levels; taste/acceptability still matters
Fe: no WHO health-based value; Al: operational residual targets, not a universal 0.2 mg/L health limit
PCBs (Polychlorinated Biphenyls) = carcinogenic industrial pollutant in water

☠️ Bhopal Gas Tragedy — night of 2–3 December 1984

Night of 2–3 Dec 1984

Date of Tragedy

Bhopal, MP

Location

UCIL

Company

MIC

Gas Leaked

Gas leaked: Methyl Isocyanate (MIC) — formula: H₃C–N=C=O
Company: Union Carbide India Limited (UCIL), Bhopal
MIC was an intermediate in pesticide manufacture, including carbaryl production
One of the worst industrial disasters in history
Thousands of people killed and injured

⚠️ Exam Trap — Bhopal

Date = night of 2–3 December 1984 (NOT 1986 which is Chernobyl)
Gas = Methyl Isocyanate (MIC) — NOT CO or CH₄
Company = Union Carbide India Limited (UCIL) (NOT Union Carbon or Union Carbonate)
MIC is used in making pesticides

♻️ Green Chemistry

📘 Green Chemistry

Design of chemical products and processes that reduce or eliminate chemical hazards to humans and the environment.

Water can be a safer solvent when suitable: non-flammable and generally low in toxicity. Green chemistry also considers the whole process.
Aim: reduce pollution at the source (prevention over cure)
12 principles of Green Chemistry

Oilzapper Technology

Developed by TERI

TERI = The Energy and Resources Institute
Oilzapper uses a microbial consortium for oil spills, oily sludge and petroleum-contaminated soil

📋 Key Environmental Terms Summary

Term	Full Form / Key Fact
DDT	Dichloro Diphenyl Trichloroethane — persistent pollutant
CFC	Chlorofluorocarbon (Freon) — depletes ozone; used in AC & refrigerators
PAN	Peroxy Acetyl Nitrate — component of photochemical smog
BOD	Biochemical oxygen demand; CPCB BOD₅ criteria: Class A ≤2 mg/L, Classes B/C ≤3 mg/L
PCBs	Polychlorinated Biphenyls — carcinogenic industrial pollutant
TERI	The Energy and Resources Institute — developed Oilzapper
MIC	Methyl Isocyanate — Bhopal Gas Tragedy (Night of 2–3 Dec 1984)

🎯 High-Yield Exam Points

DDT = Dichloro Diphenyl Trichloroethane — persistent pollutant
5 types of pollution: Air, Water, Soil, Sound, Radioactive
Greenhouse gases include CO₂, CH₄, N₂O, fluorinated gases, water vapour and ozone. SO₂ is not a principal greenhouse gas.
General smog = Reducing (Smoke + Fog + SO₂)
Photochemical smog = Oxidative (NOx + Hydrocarbons + sunlight)
PAN = Peroxy Acetyl Nitrate — in photochemical smog
Acid rain: pH < 5.6; caused by SO₂ and NO₂
Ozone depletion: CFC = Freon; used in refrigerators & AC
Ozone depletion = Stratospheric pollution
Bhopal Tragedy: night of 2–3 December 1984 | Gas = MIC (Methyl Isocyanate) | Company = Union Carbide India Limited (UCIL)
CPCB BOD₅: Class A ≤2 mg/L; Classes B/C ≤3 mg/L. No universal 5/17 ppm clean/polluted rule.
Eutrophication = depletion of dissolved O₂ due to algal bloom (nitrates/phosphates)
Cadmium: WHO health-based guideline 0.003 mg/L in the OP reference
Zinc: no WHO health-based guideline value at typical levels; acceptability/taste is the main concern
Fe: mainly acceptability; Al: operational residual targets of ≤0.1/≤0.2 mg/L by supply context
PCBs = Polychlorinated Biphenyls = carcinogenic
Green chemistry reduces hazards and waste at source; water is a potentially safer solvent where the process permits
TERI = The Energy and Resources Institute; Oilzapper technology

📋 Abbreviations Quick Reference

Abbreviation	Full Form
DDT	Dichloro Diphenyl Trichloroethane
CFC	Chlorofluorocarbon (Freon)
PAN	Peroxy Acetyl Nitrate
BOD	Biochemical Oxygen Demand
PCBs	Polychlorinated Biphenyls
MIC	Methyl Isocyanate
TERI	The Energy and Resources Institute

⚠️ Most Common Exam Traps

Acid rain pH = below 5.6 (NOT 7)
Acid rain caused by SO₂ & NO₂ (NOT CO₂)
Photochemical smog = Oxidative; General = Reducing
Ozone = Stratospheric (NOT tropospheric)
Bhopal gas = MIC (NOT CO or H₂S)
Bhopal date = Night of 2–3 Dec 1984 (NOT 1986)
BOD high = more polluted (Higher BOD = worse)
Among the listed health-based WHO values, Cd is lowest at 0.003 mg/L; this is not a universal toxicity ranking
Eutrophication = O₂ decreases in water
CFC = ozone depleter + greenhouse gas (both)

🌍 Environmental Chemistry