Environmental Issues

Human activity has grown so vast that it now strains the very systems that keep us alive. Dirty air, poisoned water, mountains of waste and shrinking forests are the price of unchecked growth. These environmental issues threaten health, wildlife and the climate, but each can be reduced with the right effort. Knowing the main forms of pollution and how they are controlled is essential exam material.

Air pollution is the presence of harmful gases and particles in the air. The main pollutants are smoke and particulate matter, carbon monoxide, sulphur dioxide and oxides of nitrogen, released mostly by vehicles, industries and the burning of fuels.

It harms breathing and the heart, damages plants, and contributes to acid rain and global warming. Control measures include:

• Electrostatic precipitators, which remove particulate matter from factory chimney smoke.
• Scrubbers, which remove harmful gases like sulphur dioxide.
• Catalytic converters in vehicles, which change harmful gases into less harmful ones, and the use of cleaner fuels like CNG.

The blanket phrase "vehicles, industries and the burning of fuels" hides which source gives which pollutant. The detail is heavily tested.

• Fossil-fuel power plants: the single largest source of sulphur dioxide emissions. Coal combustion at thermal power plants releases carbon dioxide alongside sulphur dioxide and oxides of nitrogen, all three together.
• Coal ash: the residue left after coal burns. It contains arsenic, lead and mercury. Indian coal has a high ash content, so this residue is produced in large amounts.
• Steel industry: emits sulphur oxides, oxides of nitrogen, carbon monoxide and carbon dioxide.
• Copper smelting: releases sulphur dioxide. The leftover copper slag can leach heavy metals into soil and water. Carbon monoxide is not the main concern here.
• Furnace oil: a thick fuel left over from refining crude oil. Some industries burn it to generate power, and doing so causes sulphur emissions.
• Crop and biomass residue burning: farmers burning leftover straw release carbon monoxide, methane, sulphur dioxide and ground-level ozone.
• Reactive nitrogen: agricultural soils release nitrogen oxides. Cattle and the poultry industry release ammonia, a reactive nitrogen compound.
• Benzene: a harmful hydrocarbon. Its main sources are automobile exhaust, tobacco smoke and wood burning. Varnished furniture and polyurethane foam are not significant sources.
• Magnetite particles: tiny iron-oxide particles that come from vehicle brakes, vehicle engines and power plants. They do not come from microwaves or telephone lines.

Acid rain is caused specifically by sulphur dioxide and oxides of nitrogen. These gases dissolve in rainwater to form acids. Carbon monoxide, ozone and the oxides of carbon do not cause acid rain.

Photochemical smog is a brown haze that forms in strong sunlight. Sunlight drives reactions among nitrogen dioxide, ozone and hydrocarbons in the air. The products include peroxyacetyl nitrate (PAN) and ground-level ozone. Both irritate the eyes and lungs.

The World Health Organization (WHO) Air Quality Guidelines set safe limits for PM2.5, the finest particulate matter. The recommended annual mean is 5 micrograms per cubic metre, and the 24-hour mean is 15 micrograms per cubic metre. These fine particulates are dangerous because they penetrate the lung barrier and pass into the bloodstream. Excess ozone in the air triggers asthma attacks.

Hydrogen-enriched CNG (H-CNG) is plain compressed natural gas blended with hydrogen. Burning it reduces carbon dioxide and hydrocarbon emissions compared with ordinary CNG. Hydrogen can be blended up to about 18 to 20 per cent by volume.

Water pollution is the contamination of rivers, lakes and groundwater. The chief sources are domestic sewage, industrial effluents, and the run-off of fertilisers and pesticides from farms.

A key concept is eutrophication. Fertiliser run-off adds nutrients to a water body. Algae then grow explosively into an algal bloom. The bloom dies and decays, using up the oxygen and killing fish and other life. Sewage is measured by its Biochemical Oxygen Demand (BOD). The higher the BOD, the more polluting the waste. Water is cleaned by treating sewage and effluents before release.

Eutrophication in the sea has extra triggers. Harmful algal blooms in seawater are driven by nutrient discharge from estuaries (the mouths where rivers meet the sea), by monsoon run-off from the land, and by upwelling, the rising of nutrient-rich deep water to the surface.

India also faces chemical contamination of drinking water. Arsenic, fluoride and uranium all occur as drinking-water pollutants in parts of the country.

Several methods treat water before or after it is polluted. Each tends to suit a particular contaminant.

• Activated carbon: a treated form of carbon with a very large surface area. It adsorbs heavy metals from effluents, meaning the metals stick to its surface. It can be made from carbon-rich waste material.
• Biofilters: beds of bacteria used in a Recirculating Aquaculture System (RAS), a fish-farming setup that reuses its water. The bacteria carry out nitrification, converting the ammonia in fish waste into nitrate. Biofilters do not remove uneaten feed and do not add phosphorus.
• Bioremediation: using living organisms to clean pollution. It enhances the natural breakdown of pollutants, and genetically engineered microorganisms can be used. It works poorly on heavy metals such as cadmium and lead, which cannot be readily or completely removed this way.
• Pseudomonas: a genetically engineered bacterial strain, nicknamed the "superbug", used to treat oil spills by feeding on the oil.

Bio-toilets on Indian Railways trains break down human waste using a bacterial inoculum, not a fungal one. The decomposition leaves carbon dioxide and water as its end products, not only ammonia and water vapour.

Cities generate huge amounts of solid waste (rubbish from homes, shops and industry). Managing it rests on the principle of the three R's:

• Reduce: use and waste less in the first place.
• Reuse: use items again instead of throwing them away.
• Recycle: turn waste into new products.

The first step is to segregate waste. Biodegradable waste rots naturally, like food and paper. Non-biodegradable waste does not, like plastics and metal. Biodegradable waste can be composted. Non-biodegradable waste should be recycled or safely disposed of. Dumping it in landfills pollutes soil and water.

Many everyday items contain synthetic plastics or polymers even when they do not look like plastic. Cigarette butts, eyeglass lenses and car tyres all contain such polymers. The gum base in chewing gum is also a synthetic plastic. These items therefore do not break down naturally.

Industrial leftovers can become useful raw materials rather than rubbish.

• Steel slag: the stony residue from steelmaking. It can be used as road-base construction material, to improve agricultural soil, and in cement production.
• Fly ash: the fine ash captured from coal-fired power plants. It can be used to make bricks and as a partial replacement for Portland cement. It does contain toxic trace elements, so it must be handled with care.

E-waste is discarded electronic equipment. Old computers release beryllium, cadmium, chromium, mercury and lead when broken up or dumped. They do not contain heptachlor or plutonium.

Beyond smoke and sewage, modern industry releases chemicals that poison slowly. Many of them share two dangerous traits. They are persistent, meaning they resist breaking down in the environment. They also bioaccumulate, meaning they build up in the bodies of animals and humans faster than they are excreted. Once such a chemical enters a food chain, its concentration keeps rising.

Two groups of synthetic chemicals show this pattern clearly:

• PFAS (perfluoroalkyl and polyfluoroalkyl substances): chemicals used in non-stick cookware, food packaging and water-repellent fabrics. They are called forever chemicals because they do not degrade easily. They are now widespread in drinking water and food, and persistent exposure leads to bioaccumulation in animal bodies.
• Brominated flame retardants: chemicals added to mattresses, upholstery and electronics to slow fires. They are highly resistant to degradation and accumulate in the fatty tissues of humans and animals.

Heavy metals raise the same concerns. Mercury enters the environment from artisanal gold mining, where it is used to bind gold particles in an amalgam, and from coal-based thermal power plants, since burning coal releases the mercury it contains. There is no known safe level of mercury exposure. Mercury is also why used fluorescent lamps must be disposed of carefully. Inside the lamp, an electric arc excites mercury vapour, which emits ultraviolet radiation. A phosphor coating on the glass then converts that ultraviolet energy into visible light. Broken or dumped lamps release the mercury.

Lead is hazardous whether inhaled or ingested, and it harms the brain and nervous system. Adding lead to petrol has been banned, yet exposure continues from lead smelting units and lead-based paints. Pencil "lead" is a common trap: it is actually graphite and poses no lead risk, and ordinary hair oils and cosmetics are not significant sources.

Nanoparticles are particles measured in billionths of a metre. They are not only human-made: nature produces them too, for example in volcanic eruptions. Industry uses nanoparticles of metallic oxides such as titanium dioxide and zinc oxide in sunscreens and cosmetics. The concern is that engineered nanoparticles released from products can contaminate water and soil, enter food chains, and trigger the production of free radicals, reactive molecules that damage living cells.

Deforestation is the clearing of forests for farmland, timber, mining and building. India's forest cover is well below the level a healthy environment needs.

Its consequences are severe: loss of biodiversity, soil erosion, disturbed water cycles, and the release of stored carbon that worsens climate change. The remedies combine law and community action. Afforestation means planting new forests. Strict forest protection limits further clearing. People's movements also matter. In the Chipko Movement, villagers hugged trees to stop them being felled. Joint Forest Management involves local communities in protecting and sharing forests. It has become an important approach.