Environmental Pollution

1. Chemical oxygen demand (COD) represents the total amount of oxygen required to oxidize organic and inorganic matter, and it is the highest in sewage water.
2. Dissolved oxygen (DO) is usually low in sewage due to microbial activity.

Concept: Itai-Itai disease is a painful condition caused by chronic poisoning from the heavy metal cadmium. The disease was first reported in the Toyama Prefecture of Japan in the early 20th century. Cadmium pollution occurred due to the release of industrial waste from mining activities into nearby rivers. The contaminated water was used for irrigation, leading to cadmium accumulation in rice crops. Long-term consumption of this contaminated rice caused severe cadmium poisoning in humans. Cadmium mainly affects the kidneys and bones.
Step 1: Understanding the meaning of "Itai-Itai".
The term “Itai-Itai” in Japanese means “ouch-ouch”, referring to the intense bone pain experienced by patients suffering from the disease.
Step 2: Effects of cadmium poisoning.
Cadmium accumulation in the body leads to:

• Severe bone pain
• Bone softening (osteomalacia)
• Kidney damage
• Fragile bones and fractures

Step 3: Eliminating other options.

• Mercury causes Minamata disease.
• Lead causes lead poisoning affecting the nervous system.
• Arsenic causes skin lesions and arsenicosis.

Thus, the heavy metal associated with Itai-Itai disease is Cadmium.

Concept: Minamata disease is a severe neurological disorder caused by poisoning from methylmercury, an organic form of mercury. It occurs when humans consume fish or shellfish contaminated with mercury compounds released into water bodies. The disease was first discovered in 1956 in Minamata Bay, Japan, where industrial wastewater from a chemical factory discharged mercury into the sea. This mercury accumulated in aquatic organisms and entered the human food chain through biomagnification. Exposure to methylmercury damages the central nervous system, leading to serious health problems.
Step 1: Identifying the toxic chemical responsible.
The primary chemical responsible for Minamata disease is methylmercury, which is a highly toxic compound of mercury. It accumulates in fish and shellfish and enters the human body through consumption.
Step 2: Understanding the symptoms caused by mercury poisoning.
Some common symptoms of Minamata disease include:

• Loss of coordination
• Numbness in hands and feet
• Muscle weakness
• Vision and hearing impairment
• In severe cases, paralysis and death

Since the disease is caused by mercury contamination, the correct answer is Mercury.

Concept: Earth’s atmosphere is divided into several layers based on temperature variation with altitude. These layers are:

• Troposphere – The lowest layer where weather phenomena occur.
• Stratosphere – The second layer that contains the ozone layer.
• Mesosphere – The layer where meteors burn up.
• Thermosphere – The upper layer where auroras occur and satellites orbit.

The ozone layer is a region rich in ozone ( ) molecules located mainly in the stratosphere, approximately – km above the Earth's surface. It plays a crucial role in absorbing harmful ultraviolet (UV) radiation from the Sun.
Step 1: Identifying the atmospheric layer containing ozone.
The ozone layer is concentrated in the stratosphere, where ozone molecules absorb most of the Sun's harmful ultraviolet radiation.
Step 2: Eliminating other options.

• Troposphere: Contains weather systems but not the ozone layer.
• Mesosphere: Known for meteor burning, not ozone concentration.
• Thermosphere: Very thin air, contains ionized gases but not the ozone layer.

Thus, the correct atmospheric layer containing the ozone layer is the Stratosphere.