Environmental Issues: One Mark Questions, Book Back Answers and Notes

About Environmental Issues

Medium ~90 min study

Human activity is changing the environment faster than natural systems can recover. Industries, growing cities, vehicles and intensive farming release substances that alter air, water and soil. This chapter explains the physical, chemical and biological changes involved and why they threaten both people and other organisms.

The chapter links each type of pollution to its wider effects. Burning fossil fuels adds greenhouse gases and causes acid rain. CFCs thin the ozone layer. Sewage and fertiliser runoff cause eutrophication of lakes. A pesticide sprayed on a field can reach a fish-eating bird many steps up the food chain in a far higher concentration. Local pollution thus becomes a regional or global problem that affects food security and public health.

For the exam, learn the definitions exactly: pollution, BOD, biomagnification and eutrophication. Remember the DDT example and know that noise is measured in decibels. Know the case studies too, such as the decentralised wastewater treatment system at Auroville and the shift from chemical fertilisers to organic farming. These are good material for application-based questions.

What you'll learn

• Classify pollutants as rapidly degradable, slowly degradable or non-degradable, with examples.
• Explain how biomagnification happens in a food chain and describe its effect on fish-eating birds.
• Describe how nutrient enrichment leads to eutrophication and a rise in BOD.
• Suggest methods to manage municipal, medical and electronic waste.
• Explain how ecosan toilets save water and produce manure.
• Name the Indian laws and rules that control air, water and noise pollution.

Before you start

• Food chains and trophic levels in an ecosystem.
• The basic structure and working of the respiratory and circulatory systems.
• The uses of fertilisers and pesticides in agriculture.

Environmental Issues explained

Pollutants, Their Effects and Solutions

Pollution and Air Quality

Pollution is any undesirable change in the physical, chemical or biological characteristics of air, water or land. Air pollution comes mainly from burning fossil fuels, industrial emissions and vehicle exhaust, which release carbon monoxide, sulphur dioxide, nitrogen oxides and particulate matter. These cause respiratory diseases, worsen asthma and damage crops and other plants. On a larger scale they produce photochemical smog, acid rain and global warming. Ozone depletion in the stratosphere is caused mainly by chlorofluorocarbons (CFCs). Control measures include catalytic converters in vehicles and electrostatic precipitators in factories, backed by the Air (Prevention and Control of Pollution) Act, 1981 and Bharat Stage emission norms.

Water Pollution and Eutrophication

Water becomes polluted when domestic sewage, industrial effluents or farm runoff change its quality, so that it harms aquatic life and is unsafe to drink. Point sources such as sewage outlets and non-point sources such as runoff from fields add nitrates and phosphates to lakes. These nutrients cause algal blooms. When the algae die, bacteria decompose them and use up the dissolved oxygen, so the biochemical oxygen demand (BOD) rises. This process is eutrophication. Fish die, and the lake ages much faster than it would naturally. One solution is integrated, decentralised wastewater treatment, as at Auroville near Puducherry, where wastewater is cleaned and reused locally.

Biomagnification

Biomagnification is the increase in concentration of a non-biodegradable toxic substance at each successive trophic level of a food chain. When chemicals such as mercury or DDT enter a water body, organisms cannot break them down or excrete them. The chemicals collect in fatty tissues and pass to the next level when the organism is eaten. A consumer eats a large amount of food from the level below, so the toxin becomes more concentrated at every step. In fish-eating birds, high DDT levels disturb calcium metabolism. The birds lay thin-shelled eggs that break early, and their populations fall.

Noise Pollution and Agrochemicals

Noise is unwanted sound, measured in decibels (dB), from vehicles, factories, loudspeakers, firecrackers and aircraft. Continued exposure to noise above about 85 dB can cause permanent hearing loss. Loud noise can also raise blood pressure, cause stress and sleep disturbance, and reduce concentration. It also disturbs animals, including marine animals affected by shipping and offshore activity. Under the Noise Pollution (Regulation and Control) Rules, 2000, permitted levels depend on the zone. In residential areas the limit is 55 dB by day and 45 dB at night; industrial areas are allowed more and silence zones near hospitals and schools less. Planting trees around noisy areas, maintaining vehicles and machines, and giving workers ear plugs and ear muffs help. Overuse of chemical fertilisers and pesticides kills useful bacteria and soil organisms, causes eutrophication and is linked to colony collapse syndrome in honeybees. Organic farming avoids these chemicals and keeps soil healthy over the long term.

Solid Waste Management and Ecosan Toilets

Cities produce large amounts of municipal solid waste, medical waste and electronic waste, much of it non-biodegradable. Open dumps and landfills can let toxic leachate seep into groundwater. Burning mixed waste, especially plastics, releases dioxins, which can cause cancer. Good waste management depends on segregation at source, composting and vermicomposting, and following refuse, reduce, reuse and recycle. Ecological sanitation (ecosan) toilets are dry composting toilets that handle human excreta without flushing water. They reduce the amount of wastewater produced and turn the waste into organic manure that can replace chemical fertilisers. Ecosan toilets are in use in parts of India and Sri Lanka.

Common mistakes to avoid

• Confusing biomagnification with bioaccumulation. Bioaccumulation is the build-up of a toxin inside one organism over time; biomagnification is the increase in concentration from one trophic level to the next.
• Thinking a high BOD means clean water. A high BOD means the water has a lot of organic matter, so microbes use up more oxygen and less is left for fish.
• Assuming noise pollution affects only hearing. Loud noise also raises blood pressure, causes stress and sleeplessness, and disturbs animals.
• Treating eutrophication as purely man-made. Natural eutrophication is a slow ageing of lakes over a very long time; human activity speeds it up, which is called accelerated or cultural eutrophication.
• Thinking ecosan toilets are unhygienic. When run properly, the waste is dried and composted until it is safe to use as manure.

Test yourself on these with the practice test, then check the worked reasoning in the solved MCQs.

Frequently asked questions

What is biochemical oxygen demand and why is it measured?

BOD is the amount of oxygen used by microorganisms to break down the organic matter in a sample of water. It indicates water quality. A high BOD means the water carries a lot of organic waste, dissolved oxygen falls, and fish and other aquatic animals can die.

How does biomagnification harm fish-eating birds?

Non-degradable chemicals such as DDT build up in fish and become more concentrated at each step up the food chain. Fish-eating birds therefore receive very high doses. DDT disturbs their calcium metabolism, so they lay thin-shelled eggs that break before hatching, and their numbers fall.

What is the difference between natural and accelerated eutrophication?

Natural eutrophication is the slow ageing of a lake as nutrients and silt build up over a very long time. Accelerated or cultural eutrophication is caused by human activity: sewage, industrial effluents and fertiliser runoff load the water with nutrients quickly, causing algal blooms and oxygen loss within a few years.

Why are dioxins a concern in waste management?

Dioxins are highly toxic compounds released when mixed waste, especially plastics and electronic waste, is burned. They spread through the air, settle on soil and water, build up in food chains and can cause cancer and reproductive problems in humans. This is why open burning of waste should be avoided.

How do ecosan toilets work?

Ecological sanitation toilets are dry composting toilets that collect human excreta without using flush water. Because no water is used, they reduce wastewater production. The waste is dried and composted until it is safe, and the nutrients are recovered as organic manure that can replace chemical fertilisers.

How do trees and green belts reduce noise pollution?

Trees and shrubs absorb and scatter sound, so rows of them planted along highways, around industries and near homes act as natural sound barriers. This lowers the noise level that reaches people living nearby, and it works best together with other measures such as maintaining vehicles and machines.