Excess of which substance in drinking water causes fluorosis, a disease that mottles teeth and deforms bones?
- A.Fluoride
- B.Chloride
- C.Sulphate
- D.Magnesium
Correct answer
Explanation
The correct answer is A, fluoride. A small quantity of fluoride in drinking water protects teeth against decay, but when the concentration rises above the permissible limit it causes fluorosis. Dental fluorosis mottles and discolours the teeth, and skeletal fluorosis stiffens the joints and bends the bones; it is a serious problem in parts of Rajasthan, Gujarat, Andhra Pradesh and Telangana, where the groundwater is naturally rich in fluoride. Option B is wrong because chloride mainly affects the taste of water and at high levels its salinity. Option C is wrong because sulphate in excess has a laxative effect but does not cause fluorosis. Option D is wrong because magnesium, along with calcium, is what makes water hard, affecting soap lather and boilers. The remedy is defluoridation or providing water from an alternative source.
Read the full article: Water Pollution and River Cleaning: Causes and Schemes
Practice Questions
View allWhich pollution causes Itai-Itai disease in human beings?
- A.Mercury pollution
- B.Cadmium pollution
- C.Arsenic pollution
- D.Nitrate pollution
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Itai-Itai disease was first identified in Japan among people who ate rice grown with water polluted by cadmium from mining waste.
Read the full explanation →Minamata disease is caused by the pollution of water with which metal?
- A.Lead
- B.Mercury
- C.Cadmium
- D.Chromium
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Minamata disease takes its name from Minamata Bay in Japan, where a factory discharged mercury compounds that were converted by bacteria into methylmercury, concentrated in fish through biomagnification and then eaten by people.
Read the full explanation →A high value of biochemical oxygen demand in a water sample indicates:
- A.The water is clean and fit to drink
- B.Heavy load of organic pollution
- C.High dissolved oxygen
- D.Absence of bacteria
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Biochemical oxygen demand measures the oxygen that micro-organisms need in order to break down the organic matter present in a sample.
Read the full explanation →Blue baby syndrome, or methaemoglobinemia, in infants is caused by an excess of which substance in drinking water?
- A.Fluoride
- B.Nitrate
- C.Iron
- D.Calcium
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Nitrate from fertiliser run-off and from sewage seeps into groundwater; in an infant it is converted to nitrite, which binds to haemoglobin and forms methaemoglobin, a compound that cannot carry oxygen.
Read the full explanation →The excessive growth of algae in a water body due to enrichment with nitrates and phosphates is called:
- A.Biomagnification
- B.Eutrophication
- C.Salinisation
- D.Sedimentation
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When fertilisers, detergents and sewage add nitrates and phosphates to a lake or a slow-moving river, algae multiply into a bloom that covers the surface.
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