Test: Air Pollution, Water Pollution & Their Control (Old NCERT) - NEET MCQ

► A collective increase in the concentrations of a persistent substance such as heavy metals, pesticides, etc. as we move up the food chain is known as biomagnification. 

► Biomagnification is the reason that causes maximum pollution to occur in tertiary consumers as toxins or pollutants are concentrated in an organism as in the food chain, larger animals continue to eat smaller animals.

Difference between Biomagnification and Bioaccumulation:

Normal, clean rain has a pH value of between 5.0 and 5.5, which is slightly acidic. However, when rain combines with sulfur dioxide or nitrogen oxides—produced from power plants and automobiles—the rain becomes much more acidic.
Typical acid rain has a pH value of 4.0. A decrease in pH values from 5.0 to 4.0 means that the acidity is 10 times greater.

Since large populations of Escherichia coli are found in the human colon, the presence of E. coli in water indicates that it has been contaminated with faecal matter. Thus, E. coli is commonly known as an indicator of water pollution. 

Image of Escherichia coli:

Nutrient enrichment of water bodies causes eutrophication.
Eutrophication is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae. This process may result in oxygen depletion of the water body.

Illustration of Eutrophication:

►Herbicides, also commonly known as weedkillers, are chemical substances used to control unwanted plants. 
►Selective herbicides control specific weed species, while leaving the desired crop relatively unharmed. 

• The type of air pollution caused by photochemical smog is formed through the reaction of solar radiation with airborne pollutants like nitrogen oxides and volatile organic compounds.
• These compounds, which are known as primary pollutants, are often introduced into the atmosphere through automobile emissions and industrial processes.
  Ultraviolet light can split nitrogen dioxide into nitric oxide and monatomic oxygen, this monatomic oxygen can then react with oxygen gas to form ozone.
• Products like ozone, aldehydes, and peroxyacetyl nitrates are known as secondary pollutants.
• The mixture of these primary and secondary pollutants forms photochemical smog.

Thus, the correct answer is option C.

Photochemical smog formation; sunlight reacts with NO₂ which then interacts with other molecules in the air to form smog:

Biomagnification refers to an increase in the concentration of the toxicant at successive trophic levels.
This happens because a toxic substance accumulated by an organism cannot be metabolized or excreted and is thus passed on to the next higher trophic level. This phenomenon is well known for mercury and DDT.

Domestic sewage rich in organic waste will exert a very high demand for oxygen in order to get biodegraded. Thus depleting the dissolved oxygen below the critical level necessary to support aquatic life.

Especially fish, which is very sensitive to the dissolved oxygen available in water, starts dying if the level goes below 4 mg/L.

► PAN (Peroxyacetyl nitrate) is an important constituent of photochemical smog. It is a secondary pollutant.

► A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

The loudness above 60-80 dB, is not much uncomfortable while prolonged exposure to the noise level above 80 dB is painful and gradually leads to permanent loss of hearing ability or deafness.