Maarg Manthan · Topic 13.20

Respiratory Irritants and Toxic Chemicals in Air Pollution

Environment & Ecology › Air, Marine, Noise and Other Pollution · Topic 13.20

Air contains many chemicals that irritate or poison the respiratory system and body. Respiratory irritants include sulphur dioxide, nitrogen dioxide, ozone, ammonia, chlorine, formaldehyde and acid mists, along with fine particles; they inflame the nose, throat and lungs and cause cough, wheezing, asthma attacks and bronchitis. Toxic chemicals in air include carbon monoxide, which blocks oxygen transport; hydrogen sulphide and hydrogen cyanide, which poison cells; heavy metals such as lead and mercury; volatile organic compounds such as benzene, a cause of leukaemia; polycyclic aromatic hydrocarbons such as benzo(a)pyrene, linked to lung cancer; dioxins and furans from waste burning; asbestos fibres; and industrial gases such as methyl isocyanate and phosgene. Sources are vehicles, industry, waste burning, indoor smoke, solvents and tobacco. The Bhopal gas tragedy of 2 and 3 December 1984, caused by a leak of methyl isocyanate from the Union Carbide plant, killed thousands and injured over half a million people. It led to the Environment (Protection) Act, 1986 and the Public Liability Insurance Act, 1991.

5 min read · UPSC Prelims · Environment & Ecology · Air, Marine, Noise and Other Pollution

At a Glance

Irritants SO2, NO2, ozone, ammonia
Poisons CO, H2S, benzene, PAHs
Disaster Bhopal, 1984
Gas Methyl isocyanate
Laws after EPA 1986, PLI Act 1991
Exam link UPSC Prelims, Environment & Ecology: Air, Marine, Noise and Other Pollution

Where Does It Fit?

This topic returns to air pollution with a focus on health. It follows thermal pollution and links to the Bhopal disaster, which shaped Indian environmental law. Previous topic: Thermal Pollution: Causes, Effects and Control. Next topic: Bottom Trawling and Its Impact on Deep-Sea Fishing.

Which Chemicals Irritate or Poison Through Air?

Type	Examples and effects
Respiratory irritants	SO2, NO2, ozone, chlorine, ammonia, formaldehyde and acid mists inflame airways; cause cough, asthma attacks and bronchitis
Systemic poisons	Carbon monoxide blocks oxygen transport; hydrogen sulphide and cyanide disrupt cell respiration
Carcinogens	Benzene, benzo(a)pyrene and other PAHs, asbestos, formaldehyde, dioxins and some metals
Heavy metals	Lead damages the brain and blood, mercury vapour harms the nervous system
Volatile organic compounds	Solvents, fuels, paints that evaporate into air and may cause headaches and cancer
Industrial accident gases	Methyl isocyanate, phosgene, chlorine and ammonia leaks
Particles carrying toxics	Fine particles carry metals and organic toxins deep into the lungs

What Happened at Bhopal and What Changed?

Date and place: 2 to 3 December 1984, Union Carbide pesticide plant, Bhopal, Madhya Pradesh
Gas: methyl isocyanate (MIC), used to make the pesticide Sevin, leaked after water entered a storage tank
Impact: thousands died within days, and over half a million were injured, with lasting illness
Causes: design and safety failures, poor maintenance, lack of emergency planning and weak regulation
Law: Environment (Protection) Act, 1986 was enacted after the disaster
Compensation: Bhopal Gas Leak Disaster (Processing of Claims) Act, 1985 and a settlement in 1989
Public Liability Insurance Act, 1991: requires owners of hazardous plants to insure for relief
Other rules: Manufacture, Storage and Import of Hazardous Chemicals Rules, 1989; Chemical Accidents Rules, 1996

What Else Should You Remember?

Carbon monoxide: binds haemoglobin and causes poisoning in closed spaces
Hydrogen sulphide: smells like rotten eggs at low levels but paralyses the sense of smell at high levels
Hydrogen cyanide: released from burning plastics and some industries
Benzene: found in petrol; NAAQS annual limit is 5 micrograms per cubic metre
PAHs: formed by incomplete combustion, found in smoke and soot
Dioxins and furans: released from waste burning and some chemical processes; persistent and toxic
Asbestos: fibres that cause asbestosis and mesothelioma
Formaldehyde: released from furniture, glues and indoor sources
Indoor air: cooking smoke, tobacco, cleaning products and moulds
Tobacco smoke: contains hundreds of toxic compounds
COPD: chronic obstructive pulmonary disease, a long-term lung condition
Asthma: airway inflammation triggered by irritants and allergens
Occupational exposure: miners, construction and factory workers face dust and chemicals
Silicosis: lung disease from silica dust in mines and stone work
Vizag gas leak: LG Polymers, 7 May 2020, a leak of styrene vapour killed several people
Chemical Accidents Rules: form crisis groups at national, state and district levels
National Disaster Management Act, 2005: covers chemical disasters
NGT Act, 2010: provides quick relief for environmental accidents
Polluter pays: principle applied in the Oleum gas leak case of 1986 (M C Mehta) with absolute liability
Absolute liability: a Supreme Court doctrine for hazardous industries
Link to previous: see Thermal Pollution: Causes, Effects and Control
Link to next: see Bottom Trawling and Its Impact on Deep-Sea Fishing
Link to air pollution: see Top Ten Air Pollutant Gases and Control Measures
Caution: casualty figures for Bhopal vary by source, so quote them as approximate
Exam hint: connect Bhopal to MIC and to the laws that followed
Toxic chemicals: industrial toxic chemicals include solvents, pesticides, metals and gases that can leak or be emitted in routine operation
Sick building syndrome: indoor irritants such as VOCs and formaldehyde cause headaches and eye irritation in poorly ventilated offices
Right to know: communities near hazardous plants should have access to information on chemicals and emergency plans
Onsite and offsite emergency plans: hazardous units must prepare plans, drills and alarms that include nearby residents

Why Does It Matter for the Exam?

Disaster: Bhopal 1984
Gas: MIC
Law: EPA 1986, PLI 1991
Current affairs link: Vizag leak 2020
Common errors: naming phosgene as the Bhopal gas

As an analytical point, toxic air pollution ranges from daily low-level exposure to sudden industrial accidents. Bhopal showed that law, planning and community right-to-know must be in place before disaster strikes.

Why Is This Topic Important?

Irritants Lungs
Poisons Body
Lesson Bhopal

What Came Next?

The next topic covers bottom trawling and its impact on deep-sea fishing. Next topic: Bottom Trawling and Its Impact on Deep-Sea Fishing.

Key People and Terms

MIC Methyl isocyanate
PAH Polycyclic aromatic hydrocarbon
VOC Volatile organic compound
Carcinogen Cancer-causing agent
Absolute liability No-fault strict liability
PLI Act Public Liability Insurance Act

Exam Corner

Points to Remember

Bhopal gas: MIC, 1984.
EPA passed in 1986.
PLI Act in 1991.
CO binds haemoglobin.
Benzene causes leukaemia.

Do Not Confuse With

Irritant and poison Local airway harm versus whole-body harm
Bhopal and Vizag leaks MIC in 1984 versus styrene in 2020
Strict and absolute liability No-fault with exceptions versus no exceptions

Memory Hook

Eighty-four Bhopal, MIC leak, eighty-six law, ninety-one insure.

Mains Angle

Questions ask for examples and laws. These points help.

Types Irritants, toxics
Case Bhopal
Laws EPA, PLI

A Question You May Face

An original practice question, not a past paper question.

“Discuss the health effects of toxic air pollutants and the lessons of the Bhopal gas tragedy for industrial safety in India.”

How to Answer

Types Irritants, poisons.
Effects Lungs, cancer.
Bhopal MIC.
Laws EPA, PLI.

GS Relevance

Prelims: irritants, toxic gases, Bhopal. GS Paper 3: industrial disasters and air toxics.

Frequently Asked Questions

What are respiratory irritants in air?

Respiratory irritants are gases and particles that inflame the nose, throat and lungs, such as sulphur dioxide, nitrogen dioxide, ozone, ammonia, chlorine, formaldehyde, acid mists and fine particles. They cause cough, wheezing, breathlessness, asthma attacks and bronchitis, and long exposure can cause chronic lung disease, especially in children and the elderly.

What are the main toxic chemicals in polluted air?

Toxic air chemicals include carbon monoxide, hydrogen sulphide, hydrogen cyanide, benzene and other volatile organic compounds, polycyclic aromatic hydrocarbons, lead, mercury vapour, dioxins and furans, asbestos fibres, and industrial gases like methyl isocyanate and phosgene. Some cause cancer, brain or organ damage, or birth defects.

What was the Bhopal gas tragedy?

On the night of 2 to 3 December 1984, methyl isocyanate gas leaked from the Union Carbide pesticide plant in Bhopal after water entered a storage tank. Thousands of people died within days and more than half a million were injured, many with lasting illness. It is among the world's worst industrial disasters.

What laws followed the Bhopal disaster?

The Environment (Protection) Act, 1986 was passed to provide a framework for environmental protection. The Public Liability Insurance Act, 1991 requires owners of hazardous installations to take insurance for relief to victims. Rules on hazardous chemicals, chemical accidents and disaster management were also framed, and courts developed absolute liability for hazardous industries.

Why is benzene a health concern?

Benzene is a volatile organic compound present in petrol, vehicle exhaust, solvents and tobacco smoke. Long exposure damages bone marrow and blood cells and causes leukaemia. India's air quality standards set an annual limit of 5 micrograms per cubic metre, and fuel quality norms limit its content in petrol.

PYQ Practice — Statement Analysis

1 Methyl isocyanate leaked in the Bhopal disaster.

True

In December 1984.

2 The Public Liability Insurance Act was passed in 1986.

False

In 1991.

3 Carbon monoxide reduces oxygen transport in blood.