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Water, soil and noise pollution

தமிழில் விளக்கம்

Pollution · Part 2 / 3 · Fact-checked on 8 November 2026 · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

Point and non-point sources; dissolved oxygen, BOD and COD; eutrophication; mercury, cadmium and lead; arsenic, fluoride and nitrate in groundwater; sewage treatment, the Ganga Action Plan and Namami Gange; bioremediation and phytoremediation; soil pollution, bioaccumulation and biomagnification; the Noise Rules, 2000; thermal, radioactive and light pollution and oil spills.

Each idea is explained first in Tamil (தமிழ்), ending with the English and Hindi exam terms, followed by the same point in exam English. UPSC Prelims is in English or Hindi, so understand it in Tamil and revise it in English.

ஊர்க் குளத்தில் ஒரு தொழிற்சாலைக் குழாய் கழிவு நீரை விடுகிறது என்று வைத்துக்கொள்ளுங்கள். அந்தக் குழாய் கண்ணுக்குத் தெரியும், அதைப் பிடித்து அபராதம் போடலாம்; இதுதான் புள்ளி மூலம். ஆனால் மழையில் ஆயிரக்கணக்கான வயல்களிலிருந்து உரமும் பூச்சிக்கொல்லியும் அடித்து வந்து குளத்தில் சேர்ந்தால், எந்த ஒரு குழாயையும் அடைக்க முடியாது; இது புள்ளியற்ற மூலம். இதைத் தடுக்க விவசாயிகளும் நகரங்களும் பழக்கத்தை மாற்ற வேண்டும், அதனால்தான் இது கடினம். (→ English: water pollution; point source; non-point source · हिन्दी: जल प्रदूषण; बिंदु स्रोत; गैर-बिंदु स्रोत)

In exam EnglishThe first part of this chapter dealt with air; this second part turns to water, soil and noise. Water counts as polluted once its physical, chemical or biological make-up has been altered enough to hurt the people, crops or creatures that depend on it. A point source is a single outlet that can be identified, such as a factory's effluent pipe or a town's sewage drain emptying into a river; because the outlet is known, it can be monitored, given consent conditions and penalised. A non-point source is spread out: rain washing fertiliser and pesticide off thousands of fields, or oil and litter off city streets. There is no single pipe to block, so control depends on changing what people do on the land, which makes non-point pollution the harder problem.

நீரை மூன்று அளவீடுகளால் சோதிக்கிறார்கள். கரைந்த ஆக்சிஜன் என்றால் நீரில் மீன்கள் சுவாசிக்கும் காற்று. உயிர்வேதி ஆக்சிஜன் தேவை என்றால் கழிவில் உள்ள அழுக்கை பாக்டீரியா தின்னும்போது எவ்வளவு ஆக்சிஜனைச் செலவழிக்கிறது என்பது; அழுக்கு அதிகமானால் இது கூடும், மீன்களுக்கு மிஞ்சும் ஆக்சிஜன் குறையும். வீட்டில் விருந்தினர் அதிகமானால் சோறு சீக்கிரம் தீர்வது போல. வேதி ஆக்சிஜன் தேவை வலுவான வேதிப்பொருளால் எல்லாவற்றையும் எரித்து அளக்கும், பாக்டீரியா தின்ன முடியாதவற்றையும் சேர்த்து; அதனால் அது எப்போதும் அதிகம். (→ English: dissolved oxygen (DO); biochemical oxygen demand (BOD); chemical oxygen demand (COD) · हिन्दी: घुलित ऑक्सीजन; जैव-रासायनिक ऑक्सीजन माँग; रासायनिक ऑक्सीजन माँग)

In exam EnglishThree measurements tell how polluted water is. dissolved oxygen (DO) is the oxygen held in the water, which fish and other aquatic life breathe; it falls as water warms and as microbes consume it. biochemical oxygen demand (BOD) is the amount of oxygen that bacteria use up while breaking down the organic matter in a sample, usually measured over five days at 20°C. Organic waste such as sewage raises BOD and pulls DO down, so a high BOD signals heavy organic pollution. chemical oxygen demand (COD) measures the oxygen needed to oxidise the matter in the sample chemically, with a strong oxidising agent, so it also counts substances that bacteria cannot digest. For the same sample COD is normally higher than BOD. The Central Pollution Control Board's criteria for outdoor bathing water ask for DO of at least 5 mg/l and BOD of no more than 3 mg/l.

The three oxygen measures of water quality
Measure	What it measures	Polluted water shows	Test
DO	Oxygen present in the water	Low value	Direct reading
BOD	Oxygen used by microbes to decompose organic matter	High value	Five days at 20°C
COD	Oxygen needed to oxidise matter chemically, including what microbes cannot digest	High value; normally above BOD	A few hours

குளத்தில் உரமும் கழிவும் அதிகமாகக் கலந்தால் அதுதான் மிகை ஊட்டமடைதல். முதலில் பாசி திடீரெனப் பெருகி நீர் பச்சையாகிறது, கீழே உள்ள செடிகளுக்கு வெளிச்சம் கிடைக்காது. பாசி இறந்ததும் பாக்டீரியா அதை அழுகச் செய்து நீரிலுள்ள ஆக்சிஜனை எல்லாம் செலவழிக்கிறது, மீன்கள் மூச்சுத் திணறி மிதக்கின்றன. அளவுக்கு மீறி உரம் போட்ட தொட்டிச் செடி அழுகுவது போல. ஆகாயத் தாமரை குளங்களை மூடுவதும் இதே வகை நீரில்தான். (→ English: eutrophication; algal bloom; dead zone · हिन्दी: सुपोषण; शैवाल प्रस्फुटन; मृत क्षेत्र)

In exam Englisheutrophication is the over-enrichment of a lake, pond or slow-moving river with nutrients, chiefly nitrogen and phosphorus. Every lake slowly gathers nutrients and ages over centuries; human activity speeds this up enormously through fertiliser runoff, untreated sewage and phosphate detergents, and this faster version is called cultural eutrophication. Extra nutrients feed a sudden growth of algae, an algal bloom, which turns the water green and shades out the plants below. When the algae die, bacteria decompose them and use up the dissolved oxygen; BOD rises, DO crashes and fish suffocate. Some blooms of blue-green algae (cyanobacteria) also release toxins. Stretches of coastal sea left with too little oxygen for most life are called dead zones. The floating mats of water hyacinth that choke many Indian lakes thrive in the same nutrient-rich water.

கன உலோகங்கள் அழுகாது, உடலில் சேர்ந்துகொண்டே இருக்கும். ஜப்பானின் மினமாட்டாவில் ஒரு தொழிற்சாலை பாதரசத்தைக் கடலில் விட்டது; அது மீன்களில் சேர்ந்தது, அந்த மீனை உண்டவர்களின் நரம்புகள் பாதிக்கப்பட்டன. அதுவே மினமாட்டா நோய். இட்டாய்-இட்டாய் என்றால் 'வலிக்குது, வலிக்குது'; சுரங்கக் காட்மியம் நெல் வயலில் சேர்ந்து எலும்புகள் நொறுங்கும் நிலைக்கு வந்தன. மினமாட்டா என்றால் பாதரசம், இட்டாய்-இட்டாய் என்றால் காட்மியம். ஈயம் குழந்தைகளின் மூளையைப் பாதிக்கும். (→ English: heavy metals; Minamata disease (mercury); itai-itai disease (cadmium); lead · हिन्दी: भारी धातुएँ; मिनामाता रोग (पारा); इताई-इताई रोग (कैडमियम); सीसा)

In exam EnglishHeavy metals are dangerous because they do not break down and they build up in living tissue. The best-known disaster is Minamata disease. From the 1930s a chemical factory at Minamata in Japan let mercury waste flow into the bay, where it was turned into methylmercury and concentrated in fish; people who ate the fish suffered nerve damage, numbness and birth defects, and the disease was officially identified in 1956. The Minamata Convention on Mercury, adopted in 2013 and in force from 2017, is named after the town. Itai-itai disease, also from Japan (the name means 'it hurts, it hurts'), was caused by cadmium from mining that polluted the rice fields of the Jinzu river basin; it left bones brittle and painful and damaged the kidneys. Lead harms the brain and nerves, above all in children, which is one reason leaded petrol was phased out.

இந்த நஞ்சு தொழிற்சாலையிலிருந்து அல்ல, நிலத்தின் உள்ளிருந்தே வருகிறது. கங்கைச் சமவெளி மண்ணில் இயற்கையாக உள்ள ஆர்சனிக், ஆழ்துளைக் கிணறுகளால் அதிகம் இறைத்தால் கிணற்று நீருக்கு வருகிறது. பாறைகளிலிருந்து புளோரைடு நீரில் கலக்கிறது; கொஞ்சம் என்றால் பற்களுக்கு நல்லது, அதிகமானால் புளோரோசிஸ்: பற்களில் கறை, பிறகு எலும்புகள் வளைவு. உப்பு கொஞ்சம் சுவை, அதிகம் நோய் என்பது போல. உர நைட்ரேட் கைக்குழந்தைகளுக்கு 'ப்ளூ பேபி' பிரச்சினை தரும். (→ English: arsenic; fluoride; fluorosis; nitrate; blue baby syndrome · हिन्दी: आर्सेनिक; फ़्लोराइड; फ्लोरोसिस; नाइट्रेट; ब्लू बेबी सिंड्रोम)

In exam EnglishSome of India's worst water pollution cannot be seen and comes from the ground itself. Arsenic occurs naturally in the young sediments of the Ganga-Brahmaputra plains, and heavy pumping of groundwater draws it into wells in states such as West Bengal, Bihar, Uttar Pradesh and Assam; years of drinking it cause skin lesions and cancers. Fluoride comes from fluoride-bearing rocks in drier regions such as Rajasthan, Gujarat and parts of Telangana and Andhra Pradesh. A little protects teeth, but too much causes fluorosis: mottled teeth first, then stiff and deformed bones. Surplus fluoride can be settled out of water by dosing it with alum and lime, a method worked out by the National Environmental Engineering Research Institute (NEERI) and known as the Nalgonda technique. Nitrate, mostly from fertilisers and sewage, seeps into groundwater and can cause 'blue baby syndrome' (methaemoglobinaemia) in infants. The Bureau of Indian Standards' drinking water standard, IS 10500:2012, sets limits of 0.01 mg/l for arsenic, 1.0 mg/l for fluoride (1.5 mg/l where no other source exists) and 45 mg/l for nitrate.

Toxic contaminants of water and what they cause
Contaminant	Main source	Effect	Known case or area
Mercury	Industrial waste	Nerve damage, birth defects	Minamata disease, Japan
Cadmium	Mining waste	Brittle, painful bones; kidney damage	Itai-itai disease, Japan
Lead	Leaded petrol (earlier), batteries	Harm to brain and nerves, mainly in children	Phase-out of leaded petrol
Arsenic	Natural sediments, drawn up by heavy pumping	Skin lesions, cancers	Ganga-Brahmaputra plains
Fluoride	Fluoride-bearing rocks	Dental and skeletal fluorosis	Rajasthan, Gujarat, parts of Telangana and Andhra Pradesh
Nitrate	Fertilisers, sewage	Blue baby syndrome in infants	Farming areas

நதிகளில் உள்ள பெரும்பாலான அழுக்கு நகரக் கழிவுநீர்தான், எனவே முதலில் அதைச் சுத்திகரிக்க வேண்டும். கழிவுநீர் சுத்திகரிப்பு நிலையம் அரிசி கழுவுவது போலப் படிப்படியாக வேலை செய்கிறது: முதலில் சல்லடையால் கல், குப்பை நீக்கம்; பிறகு நுண்ணுயிரிகளுக்குக் காற்று கொடுத்துக் கரைந்த அழுக்கைத் தின்னச் செய்தல்; கடைசியில் சத்துகளை நீக்கிக் கிருமிகளைக் கொல்லுதல். கங்கை சுத்தம் 1985 கங்கை செயல் திட்டத்துடன் தொடங்கியது; இப்போது நமாமி கங்கே அந்த வேலையைச் செய்கிறது. (→ English: sewage treatment plant; primary, secondary and tertiary treatment; Ganga Action Plan; Namami Gange; National Mission for Clean Ganga · हिन्दी: सीवेज उपचार संयंत्र; प्राथमिक, द्वितीयक और तृतीयक उपचार; गंगा कार्य योजना; नमामि गंगे; राष्ट्रीय स्वच्छ गंगा मिशन)

In exam EnglishMost of the organic load in Indian rivers is untreated urban sewage, so treatment plants are the first line of defence. A sewage treatment plant works in stages. Primary treatment removes floating and settling solids by screening and sedimentation. Secondary treatment lets microbes consume the dissolved organic matter, often in aerated tanks (the activated sludge process), which cuts BOD sharply. Tertiary treatment adds further steps, such as removing nutrients and disinfecting, before the water is reused or released. River cleaning in India began with the Ganga Action Plan in 1985, which was widened in 1995 into the National River Conservation Plan for other rivers. The Ganga was declared a national river in 2008, and in 2015 the Union government approved Namami Gange, an integrated mission for the river. It is carried out by the National Mission for Clean Ganga, which works under the National Ganga Council chaired by the Prime Minister.

அழுக்கைச் சுத்தம் செய்ய உயிரினங்களையே வேலைக்கு வைக்கலாம். உயிரியல் தூய்மையாக்கத்தில் பாக்டீரியாவும் பூஞ்சைகளும் மாசைத் தின்று தீங்கற்ற நீர், கார்பன் டை ஆக்சைடாக மாற்றுகின்றன; கடலில் சிந்திய எண்ணெய் மீது எண்ணெய் தின்னும் பாக்டீரியாவைத் தூவுவது உதாரணம். தாவரத் தூய்மையாக்கத்தில் செடிகள் மண்ணிலுள்ள உலோகங்களை வேர்களால் உறிஞ்சுகின்றன, பிறகு அந்தச் செடிகளை அறுத்துப் பாதுகாப்பாக அகற்றுவார்கள். கடற்பஞ்சு நீரை உறிஞ்சி, பிழிந்து எடுப்பது போல. மலிவு, ஆனால் மெதுவு. (→ English: bioremediation; phytoremediation · हिन्दी: जैव उपचार; पादप उपचार)

In exam EnglishLiving things can also be put to work cleaning up. bioremediation uses microbes, mainly bacteria and fungi, to break pollutants down into harmless substances such as carbon dioxide and water. Bacteria that digest oil, spread on spills and on oily sludge, are the usual example; Oilzapper, a microbial culture developed in India by The Energy and Resources Institute (TERI), is one such product. phytoremediation uses plants instead. Some plants draw metals or other toxins out of soil or water into their roots and leaves, and are then harvested and disposed of safely; others hold the pollutants in place or break them down. Both methods are cheap and gentle compared with digging up contaminated soil and burning it, but they are slow and work best where the contamination is moderate.

மண் தாங்கும் அளவைவிட வேகமாக நஞ்சுகள் சேர்ந்தால் அது மாசடைகிறது: பூச்சிக்கொல்லி, அளவுக்கு மீறிய உரம், சுரங்க உலோகங்கள், பிளாஸ்டிக். DDT போன்ற மருந்து கொழுப்பில் ஒளிந்துகொள்ளும், வெளியேறாது; அதுவே உயிர்த் திரட்சி. உணவுச் சங்கிலியில் மேலே போகப் போக அது பெருகும்; அதுவே உயிரியல் உருப்பெருக்கம். பூச்சியிலிருந்து மீன், மீனிலிருந்து பருந்து: ஒவ்வொரு படியிலும் நஞ்சு அதிகம், சிறு கடன் வட்டியோடு வளர்வது போல. அதனால் பருந்து முட்டை ஓடுகள் மெலிந்தன. (→ English: soil pollution; bioaccumulation; biomagnification; DDT; endosulfan · हिन्दी: मृदा प्रदूषण; जैव संचयन; जैव आवर्धन; DDT; एंडोसल्फ़ान)

In exam EnglishSoil is polluted when harmful substances build up faster than it can neutralise them. Farming is a major source: pesticides that linger in the ground, and fertilisers used in excess, which acidify the soil, upset its microbes and leach nitrate into groundwater. Industry and mining add heavy metals and toxic effluent, and plastic fragments persist for decades. The most harmful pesticides are persistent and dissolve in fat, as DDT does. They stay in an animal's fat instead of being excreted, which is bioaccumulation, and their concentration rises at each step up a food chain, which is biomagnification, so top predators carry the heaviest load; DDT thinned the eggshells of birds of prey. India now allows DDT only for limited public-health use against disease-carrying mosquitoes. In 2011 the Supreme Court ordered a nationwide ban on the production, use and sale of endosulfan, after illness was linked to its aerial spraying on cashew plantations in Kasaragod, Kerala.

ஒலியை டெசிபல் அலகில் அளக்கிறார்கள். இது சாதாரண அளவுகோல் அல்ல: 10 கூடினால் ஆற்றல் பத்து மடங்கு. 70-லிருந்து 80-க்குப் போவது ஒரு படி அல்ல, பத்துப் படி ஏறுவது போல. விதிகள் பகலுக்கும் இரவுக்கும் தனித்தனி வரம்பு வைக்கின்றன; இரவு 10 மணிக்குப் பிறகு திறந்தவெளி ஒலிபெருக்கி கூடாது. மருத்துவமனை, பள்ளி, நீதிமன்றம் சுற்றி 100 மீட்டர் அமைதி மண்டலம்; அங்கே நோயாளி, மாணவர், நீதிபதி அமைதியாக இருக்க வேண்டும் அல்லவா. (→ English: decibel (dB); Noise Pollution (Regulation and Control) Rules, 2000; silence zone · हिन्दी: डेसिबल; ध्वनि प्रदूषण (विनियमन और नियंत्रण) नियम, 2000; शांत क्षेत्र)

In exam EnglishNoise is unwanted sound, measured in decibels (dB). The scale is logarithmic: every rise of 10 dB means ten times the sound energy, so 80 dB is not slightly worse than 70 dB but ten times as intense. Long exposure to loud noise causes permanent hearing loss. A 1987 amendment brought noise within the Air Act's definition of an air pollutant, but the detailed rules are the Noise Pollution (Regulation and Control) Rules, 2000, made under the Environment (Protection) Act, 1986. They set ambient limits for four kinds of area, separately for day (6 a.m. to 10 p.m.) and night (10 p.m. to 6 a.m.). The ground within 100 metres or more of a hospital, an educational institution or a court is treated as a silence zone. Loudspeakers may not be used at night except in closed premises such as halls, though a state may allow them until midnight on up to fifteen festival days a year. In 2005 the Supreme Court upheld such limits, treating freedom from noise as part of the right to life under Article 21.

Ambient noise limits under the Noise Rules, 2000 (Leq, dB(A))
Area	Day (6 a.m. to 10 p.m.)	Night (10 p.m. to 6 a.m.)
Industrial	75	70
Commercial	65	55
Residential	55	45
Silence zone	50	40

இன்னும் சில வகைகள்: வெப்ப மாசு என்றால் மின் நிலையங்கள் குளிர்விக்கப் பயன்படுத்திய சூடான நீரை ஆற்றில் விடுவது; சூடான நீரில் ஆக்சிஜன் குறைவு, அதனால் மீன்கள் இறக்கின்றன. கதிரியக்க மாசு செல்களையும் மரபணுக்களையும் சேதப்படுத்தும். நகரங்களின் அளவுக்கு மீறிய வெளிச்சம் இரவு உயிரினங்களைக் குழப்புகிறது; ஆமைக் குஞ்சுகள் கடலுக்குப் பதிலாகச் சாலையை நோக்கிப் போகும், விளக்கை நோக்கிப் பறக்கும் விட்டில் போல. சிந்திய எண்ணெய் கடற்பறவைகளின் இறகுகளை ஒட்டவைக்கும். (→ English: thermal pollution; radioactive pollution; light pollution; oil spill · हिन्दी: तापीय प्रदूषण; रेडियोधर्मी प्रदूषण; प्रकाश प्रदूषण; तेल रिसाव)

In exam EnglishA few other kinds of pollution complete the picture. thermal pollution is the release of heated water, mostly from the cooling systems of thermal and nuclear power stations and some industries; since warm water holds less oxygen, the stretch of river or coast that receives it can lose fish and other life. Radioactive pollution comes from nuclear accidents and from careless disposal of nuclear and medical waste; radiation damages cells and genes, as the accidents at Chernobyl (1986) and Fukushima (2011) showed. Light pollution, the excess artificial light of towns and cities, hides the night sky and confuses animals that are active at night; sea-turtle hatchlings, which head for the brightest horizon, can crawl inland instead of to the sea. Oil spills coat the water, cut off oxygen and light below and mat the feathers of seabirds; they are tackled with floating booms, skimmers, chemical dispersants and bioremediation.

மொத்தத்தில் இரண்டு கேள்விகள். ஒன்று: இந்தக் கழிவு எவ்வளவு ஆக்சிஜனைத் தின்கிறது? கழிவுநீரும் உரமும் ஆக்சிஜனை உறிஞ்சி குளத்தைக் கொல்கின்றன. இரண்டு: இந்த நஞ்சு எவ்வளவு காலம் நிலைக்கும்? உலோகங்கள், ஆர்சனிக், DDT அழுகாது, உடல்களில் சேரும். கட்டுப்பாடு மூலத்தைப் பொறுத்தது: குழாய்க்குச் சுத்திகரிப்பு நிலையம், வயலுக்குப் பழக்க மாற்றம், ஒலிக்கு நேர வரம்பு. அடுத்த பகுதி வீடுகள், மருத்துவமனைகள், தொழிற்சாலைகளின் திடக்கழிவு பற்றியது. (→ English: oxygen demand; persistence; point and non-point sources; solid waste · हिन्दी: ऑक्सीजन माँग; स्थायित्व; बिंदु और गैर-बिंदु स्रोत; ठोस अपशिष्ट)

In exam EnglishTwo questions tie this part together. How much oxygen does a pollutant use up? Sewage and nutrients raise BOD, lower DO and, through eutrophication, can choke a lake. How long does it last? Metals, arsenic, fluoride and persistent pesticides do not break down, so they accumulate in bodies and magnify along food chains. Control follows the source: point sources through consents and treatment plants, non-point sources through changed practices on farms and in cities, and noise through zone limits and time rules. The third part turns to solid waste and the rules that decide who must handle each kind.

Exam traps

A high BOD means more organic pollution, not cleaner water; as BOD rises, DO falls.
For the same sample COD is normally higher than BOD, because the chemical test also counts matter that microbes cannot digest.
In eutrophication most fish die from lack of oxygen when bacteria decompose the dead algae; the algae's growth itself is fed by nitrogen and phosphorus, not by heavy metals.
Minamata disease is mercury; itai-itai disease is cadmium. Both cases are from Japan; do not swap the metals.
Arsenic in the groundwater of the Ganga-Brahmaputra plains is mainly natural (geogenic), brought up by heavy pumping, not mainly industrial.
Blue baby syndrome is caused by nitrate, not by fluoride or arsenic; fluorosis is caused by fluoride.
The Noise Rules, 2000 were made under the Environment (Protection) Act, 1986, even though a 1987 amendment also brought noise into the Air Act's definition of an air pollutant.
Hospitals, educational institutions and courts each carry a surrounding silence zone of no less than 100 metres, whose limits (50 dB by day, 40 dB by night) are the strictest of the four kinds of area.

Recap

Point source: one identifiable outlet (effluent pipe, sewage drain); non-point source: diffuse runoff from farms and streets, harder to control.
DO is oxygen in water; BOD is oxygen used by microbes (five days, 20°C); COD is oxygen for chemical oxidation and is normally above BOD.
CPCB bathing-water criteria: DO at least 5 mg/l, BOD at most 3 mg/l.
Eutrophication: nitrogen and phosphorus feed an algal bloom; decomposing algae use up oxygen; fish die; dead zones form.
Minamata (mercury, identified 1956; convention 2013, in force 2017); itai-itai (cadmium); lead harms children's nerves.
Arsenic (Ganga-Brahmaputra plains, natural), fluoride (fluorosis; Nalgonda technique), nitrate (blue baby syndrome); IS 10500:2012 limits 0.01, 1.0 and 45 mg/l.
Sewage treatment: primary (solids), secondary (microbes, cuts BOD), tertiary (nutrients, disinfection); Ganga Action Plan 1985, NRCP 1995, Namami Gange 2015 run by NMCG.
Bioremediation uses microbes (Oilzapper); phytoremediation uses plants; persistent chemicals bioaccumulate and biomagnify (DDT); endosulfan banned by the Supreme Court in 2011.
Noise Rules 2000 under the EPA: four areas, day 6 a.m.-10 p.m., night 10 p.m.-6 a.m.; silence zone 100 m; no loudspeakers at night outside closed premises.
Thermal pollution lowers oxygen; radioactive pollution damages cells and genes; light pollution misleads turtle hatchlings; oil spills are fought with booms, skimmers and microbes.

Practice questions

Q1. Which one of the following combinations in a river sample points to heavy organic pollution from sewage?

High dissolved oxygen and low BOD
Low dissolved oxygen and high BOD
High dissolved oxygen and high BOD
Low dissolved oxygen and low COD

Show answer

Answer: B. Low dissolved oxygen and high BOD

Sewage is rich in organic matter, so microbes use a lot of oxygen (high BOD) and leave little in the water (low DO). High DO with low BOD describes clean water; high DO and high BOD rarely go together because heavy microbial demand pulls DO down; and organic pollution would raise COD, not keep it low.

Q2. Consider the following statements:
1. For the same water sample, chemical oxygen demand is usually lower than biochemical oxygen demand.
2. Biochemical oxygen demand is commonly measured as the oxygen used by microbes over five days at 20°C.
Which of the statements given above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2

Show answer

Answer: B. 2 only

Statement 1 is wrong: COD counts everything that can be oxidised chemically, including matter microbes cannot digest, so it is usually higher than BOD; this rules out options 1 and 3. Statement 2 is correct, so option 4 is wrong.

Q3. Consider the following pairs:
Disease : Cause
1. Minamata disease : Cadmium
2. Itai-itai disease : Cadmium
3. Blue baby syndrome : Nitrate
Which of the pairs given above are correctly matched?

1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3

Show answer

Answer: B. 2 and 3 only

Pair 1 is wrong because Minamata disease was caused by mercury (methylmercury in fish), so options 1, 3 and 4, which include pair 1, are wrong. Pair 2 (cadmium) and pair 3 (nitrate) are correct.

Q4. Consider the following statements about eutrophication:
1. It is driven mainly by excess nitrogen and phosphorus entering a water body.
2. It raises the dissolved oxygen of the water body over time, because algae release oxygen.
Which of the statements given above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2

Show answer

Answer: A. 1 only

Statement 1 is correct, so option 4 is wrong. Statement 2 is wrong: when the algae die, bacteria decomposing them use up the dissolved oxygen, so oxygen falls and fish die; options 2 and 3, which accept statement 2, are wrong.

Q5. The arsenic found in the groundwater of the Ganga-Brahmaputra plains comes mainly from:

effluents of chemical industries
natural sediments, drawn into wells by heavy pumping
arsenic-based pesticides sprayed on rice
fly ash from thermal power stations

Show answer

Answer: B. natural sediments, drawn into wells by heavy pumping

The arsenic is geogenic: it sits naturally in the young sediments and is mobilised when groundwater is pumped heavily. Industrial effluent, pesticides and fly ash can add local contamination but are not the main cause of this regional problem, so options 1, 3 and 4 are wrong.

Q6. Consider the following statements about the Noise Pollution (Regulation and Control) Rules, 2000:
1. They were made under the Environment (Protection) Act, 1986.
2. Night time under the Rules runs from 10 p.m. to 6 a.m.
3. The noise limits for a silence zone are higher than those for a residential area.
Which of the statements given above are correct?

1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3

Show answer

Answer: A. 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is wrong: silence zones have the strictest limits (50 dB by day, 40 dB by night, against 55 and 45 for residential areas), so options 2, 3 and 4, which include statement 3, are wrong.

Q7. Growing plants that draw heavy metals out of contaminated soil into their roots and leaves, and then harvesting them, is an example of:

biomagnification
phytoremediation
eutrophication
thermal pollution

Show answer

Answer: B. phytoremediation

Using plants to remove or hold pollutants is phytoremediation. Biomagnification is the rise of a persistent chemical's concentration up a food chain, eutrophication is nutrient over-enrichment of water, and thermal pollution is the release of heated water; none of them is a clean-up method.

Q8. Consider the following statements:
1. The Ganga Action Plan was launched in 1985.
2. Namami Gange is carried out by the National Mission for Clean Ganga.
3. The National Ganga Council is chaired by the Union Minister of Jal Shakti.
Which of the statements given above are correct?

1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3

Show answer

Answer: A. 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is wrong because the National Ganga Council is chaired by the Prime Minister, so options 2, 3 and 4, which include statement 3, are wrong.

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Sources

Central Pollution Control Board: Primary Water Quality Criteria for designated best uses (outdoor bathing: DO 5 mg/l or more, BOD 3 mg/l or less); water quality monitoring of rivers — https://cpcb.nic.in
The Water (Prevention and Control of Pollution) Act, 1974 (consent for discharge of effluent) — https://www.indiacode.nic.in
United States Environmental Protection Agency: nutrient pollution and eutrophication; biochemical and chemical oxygen demand; thermal discharges; oil spill response; remediation technologies — https://www.epa.gov
Minamata Convention on Mercury (adopted 10 October 2013, in force 16 August 2017), UNEP secretariat — https://www.mercuryconvention.org
World Health Organization fact sheets: mercury and health; lead poisoning; arsenic; cadmium (itai-itai disease) — https://www.who.int
Bureau of Indian Standards: IS 10500:2012, Drinking Water: Specification (arsenic 0.01 mg/l; fluoride 1.0 mg/l, 1.5 mg/l in the absence of an alternate source; nitrate 45 mg/l) — https://www.bis.gov.in
Central Ground Water Board: groundwater quality reports (arsenic, fluoride and nitrate affected areas); NEERI's Nalgonda technique for defluoridation — https://cgwb.gov.in
National Mission for Clean Ganga, Ministry of Jal Shakti: Namami Gange (approved May 2015); Ganga Action Plan (1985) and National River Conservation Plan; River Ganga (Rejuvenation, Protection and Management) Authorities Order, 2016 — https://nmcg.nic.in
Press Information Bureau: bioremediation of oil spills and oily sludge with TERI's Oilzapper — https://pib.gov.in
Supreme Court of India: Democratic Youth Federation of India v. Union of India, interim order of 13 May 2011 banning the production, use and sale of endosulfan — https://main.sci.gov.in
The Noise Pollution (Regulation and Control) Rules, 2000, with Schedule of ambient noise standards; the Environment (Protection) Act, 1986; the Air (Prevention and Control of Pollution) Act, 1981, section 2(a) as amended in 1987 — https://www.indiacode.nic.in
Supreme Court of India: In re Noise Pollution (Implementation of the Laws for Restricting Use of Loudspeakers and High Volume Producing Sound Systems), judgment of 18 July 2005 — https://main.sci.gov.in