Pollution & Waste — PPSC previous year questions

Acid rain forms when oxides of sulphur (SO_2) and oxides of nitrogen (NO_x) from burning fossil fuels dissolve in atmospheric moisture to give sulphuric and nitric acids, so both (a) and (b) are causes. Carbon dioxide makes rainwater only mildly acidic (carbonic acid, pH about 5.6) and is not counted as a cause of acid rain.

Biochemical (Biological) Oxygen Demand is the amount of dissolved oxygen that micro-organisms need to break down the organic matter in a sample of water. It is measured over a set period, usually five days at 20 °C. A high BOD means heavily polluted water, with little oxygen left for aquatic life. So BOD is the standard index of organic pollution in water systems such as rivers and sewage effluent.

Minamata disease is caused by compounds of mercury, chiefly methylmercury. The Chisso chemical factory discharged it into Minamata Bay in Japan. From the 1950s it built up in fish eaten by local people. It damages the central nervous system, causing numbness, loss of coordination, tunnel vision and deafness. Cadmium causes itai-itai disease. Cobalt deficiency affects vitamin B12 synthesis.

SPM stands for Suspended Particulate Matter — the fine solid and liquid particles (dust, smoke, soot, aerosols) that remain suspended in air and are a standard air-pollution index. Particles below 10 µm are called PM10 and those below 2.5 µm are PM2.5; the smaller ones penetrate deep into the lungs. The other expansions are not used in environmental science.

Cadmium is taken up by plants along with zinc, as the two metals are chemically similar. Chronic cadmium poisoning causes itai-itai — literally 'ouch-ouch' — disease. It was first reported in the Jinzu river basin of Toyama, Japan, where mine effluent polluted paddy fields. It builds up in the kidneys and softens the bones. Then the slightest movement is intensely painful. Mercury causes Minamata disease; chromium causes skin and lung disorders. Neither produces itai-itai.

Eutrophication is the gradual enrichment of a lake or other water body with nutrients (chiefly nitrates and phosphates), which triggers algal blooms, depletes dissolved oxygen and slowly ages the lake. Exfoliation and denudation are weathering and erosion processes on rock, and ecological succession is the orderly change of a community over time.

Both statements are true, and R explains A. Volatile organic compounds such as benzene, formaldehyde, chloroform, carbon tetrachloride and styrene come out of building materials, furnishings, carpets, paints, adhesives, plastics and cleaning products. In a closed room with poor airflow they build up. So indoor levels are often several times the outdoor level. This off-gassing directly causes the high indoor levels. That is why indoor air pollution and 'sick building syndrome' are treated as separate environmental health problems.

All four statements are correct. Microplastics are plastic pieces smaller than 5 mm. Like all plastics they are polymers, long chains built mainly of carbon and hydrogen, often with additives. Their surfaces adsorb persistent organic pollutants, which makes the particles more toxic. They enter the body when breathed in from the air and when taken in with food and water, including sea salt, fish and bottled water.

Burning stubble releases smoke, dust and gases that badly degrade air quality, so A is correct. Crop residue can indeed be turned into ethanol (second-generation ethanol) for blending with petrol, so R is also correct, but it describes an alternative use of stubble and does not explain why burning causes pollution.

Both statements swap the two layers. Stratospheric ozone (the ozone layer, high up) is the shield that absorbs harmful UV rays, while ozone in the troposphere (near the ground) is a pollutant that forms smog and irritates eyes and lungs. So both statements are incorrect.