Test: Water Pollution (Old NCERT) - NEET MCQ

River water will always have a very lowconcentration of DDT, but as we go to higher trophic levels concentration of DDT increases due to biomagnification. So carnivorous fish has high level of DDt and it is not suitable for consumption by human beings, because of presence of DDT.

Biochemical oxygen demand or BOD is the oxygen required for microbial decomposition of a unit mass of organic remains. The degree of impurity of water due to organic matter is measured in terms of BOD. A higher BOD of a river indicates that water is highly polluted.

Water hyacinth(Eichhornia crassipes) also called as " Terror of Bengal"  is the plant that sometime chokes ponds, lakes and river resulting in inbalance  of ecosystem dynamics of water bodies. It accelerates eutrophication

Biochemical oxygen demand is the measure of oxygen required by aerobic decomposers for biochemical degradation of the organic materials. BOD indicates the degree of organic pollution in water.

Eutrophication is the excessive growth of algae, plants and animals in water bodies due to the nutrient enrichment particularly with nitrogen and phosphorus. This excessive growth of planktonic algae that causes colouration of water is called algal bloom. So, the high concentration of nitrates and phosphates in water increases both the eutrophication and algal bloom.

It is the growth of planktonic algae which impart a characteristic colouration to water during algal blooms.

The higher amounts of pesticide like DDT, disturb calcium metabolism of birds resulting in thinning of egg shells and their premature breaking. This is a major cause of reduction of population of fish eating birds. Biomagnification is found in all types of food chains.

Cultural or accelerated eutrophication is nutrient enrichment of water bodies due to human activities like passage of sewage, industrial effluents and runoff from fertilised fields rich in nitrates and phosphates. Nutrients present in sewage, agriculture wastes and fertilisers cause dense growth of plants and planktonic algae.

Contamination of water with sewage is indicated by cysts of Entamoeba histolytica. E. histolytica causes infection by ingestion of mature cysts from faecal contaminated water and causes amoebiasis in human.

Escherichia coli is a member of the coliform group and is used for the analysis of water contaminated with faecal matter.

The nutrients present in domestic sewage added in lake will cause the dense growth of plants and planktonic algae. The algae use oxygen and may deoxygenate the water which led death of fishes.

Minamata (minimata) disease first reported in 1952 due to eating of fish captured from Hg-contaminated Minamata Bay of Japan. It is charcterised by diarrhoea, hemolysis, impairment of various senses, numbness of lips, hemolysis, impairment of various senses, numbness of lips, tongue, limbs, deafness, blurring of vision, mental dearrangement, meningitis and death.

The use of urea and phosphate fertilisers and pesticide spray to crop fields are passed down to lake during rains through surface runoff. The presence of extra nutrients brings about dense growth of plant and animal life. This phenomenon is called eutrophication. It will also lead to increase in the biomass of algae which causes algal bloom. This results in the drastic decrease in oxygen in the lake, which led to mass scale death of fishes.

DDT is a chlorine containing pesticide used in agriculture. DDt is rapidly passed through food chain causing biomagnification because it is stable, accumulates in the soil and concentrates in the fatty tissue or internal organs of body (as DDT is fat soluble substance). So, DDT takes may years to break down and it enters into body of other organisms with predation. So the amount of DDT biomagnifies.

The sources of phosphate pollution are sewage treatment plants, phosphate fertilisers used in agricultural fields, etc.

Fluorides are given out during refining of materials. Fluorides cause flourosis. It is a disease which is defined by mottling of teeth, abnormal bones that "are liable to fracture because flourine replaces Ca²⁺ and" makes the bones brittle. Fluoride pollution is a serious problem in many districts of Rajasthan, where excess of fluoride in water adversely affects the health of man. Many villagers have aged prematurely or became hunch backs.

Chlorinated hydrocarbons like DDT pass into the food chain and increase in amount per unit weight of organism with the rise in trophic level due to their accumulation in fat. Among the given animals, sea gull which is a fish eating bird and is present at higher trophic level, will have high levels of DDT depositon in its body.

Excess Flouride in drinking water cause teeth deformity.

(i) Bhopal gas disaster took place on the night of 2-3 December 1984 and this day is now observed as the Bhopal gas tragedy day in India to make the anniversary of the Bhopal gas disaster. This disaster took place due to the gas leak of methyl isocyanate at the Union Carbide India Limited (UCIL) pesticide plant in Bhopal. It is estimated that close to 20,000 people died and thus it is considered one of the world’s worst industrial disasters.
(ii) Sewage is a biodegradable pollutant while DDT is a non-biodegradable pollutant and this is because sewage mostly comprises of organic compounds which can be easily broken down by decomposers but DDT is known as dichlorodiphenyltrichloroethane and it is a pesticide which is non-biodegradable and thus enters the food chain and get biomagnified.
(iii)When pollutants are released from a single point it is called point-source pollution, but when it is over a large area, then it is called non-point source pollution as nonpoint sources come from many places and it is difficult to pinpoint any one particular source.
(iv) Eichhornia is the world’s most problematic aquatic weed, introduced in India for its lovely flowers, also called the ‘Terror of Bengal’ due to the devastation it produced in the ecosystems of Bengal as its natural predator was not present there. Such species are known as invasive species.
So, the correct option is ‘(ii) Sewage, DDT (iii) point source, nonpoint source’

Mercury is changed to water soluble dimethyl mercury which undergoes biomagnification. Eating poisoned animals causes deformity known as Minamata disease (first reported in 1952 due to eating of fish captured from Hg-contaminated Minimata Bay of Japan) which is characterised by diarrhoea, hemolysis, impairment of various senses, numbness of lips, tounge, limbs, deafness, blurring of vision, mental dearrangement, meningitis and death.