One of the following is not a water pollutant?

1. Analyze the question

The question asks us to identify which of the listed substances is not considered a water pollutant. A water pollutant is any substance that, when added to a water body, degrades its quality, harms aquatic life, or makes it unsuitable for human use.

2. Explain the concept

• Inorganic fertilizers (A): These contain nitrates and phosphates. When washed into water bodies, they cause eutrophication, leading to excessive algae growth that depletes oxygen, killing fish. They are major pollutants.
• Warm water affluent (B): This causes thermal pollution. Warm water holds less dissolved oxygen than cold water. When industries discharge hot water into rivers, it disrupts the ecosystem and stresses aquatic organisms.
• Oxygen gas (C): Oxygen is essential for the survival of aquatic life (fish, plants, and microorganisms). It is a natural component of water and is necessary for the aerobic decomposition of organic matter. It does not degrade water quality; rather, its presence is a sign of healthy water.
• Biodegradable waste (D): While these can be broken down by bacteria, they are still considered pollutants because their decomposition consumes large amounts of dissolved oxygen (high Biological Oxygen Demand), which can lead to "dead zones" in water bodies.

3. Show the solution

• A, B, and D are all substances that negatively alter the chemical, physical, or biological state of water.
• C (Oxygen gas) is a life-sustaining gas. It is the standard against which water quality is measured (Dissolved Oxygen levels). Adding oxygen to water does not pollute it; in fact, aeration is a process used to treat polluted water.

4. Identify the answer

The correct option is C. Oxygen gas is the only substance listed that is beneficial to the aquatic environment rather than harmful.

5. Exam Tip

When dealing with "pollution" questions in JAMB, always remember that a pollutant is defined by its negative impact on the environment. If a substance is naturally required for the survival of the ecosystem (like oxygen), it cannot be classified as a pollutant, even if it is a gas.