Biodegradable pollutants are not safe in water systems because they can cause

1. Analyze the Question

The question asks about the negative impact of biodegradable pollutants in water systems. While "biodegradable" means a substance can be broken down by microorganisms, its presence in water in large quantities creates specific environmental hazards.

2. Explain the Concept

Biodegradable pollutants (such as sewage, animal waste, or food processing waste) are organic materials. When these enter a water body:

• Microbial Decomposition: Bacteria and other microorganisms begin to break down this organic matter.
• Oxygen Depletion: This process consumes a significant amount of dissolved oxygen in the water (a process known as increasing the Biochemical Oxygen Demand or BOD).
• Consequences: As oxygen levels drop, aquatic life (like fish) dies. Furthermore, the decomposition of these pollutants can lead to the growth of harmful pathogens (bacteria, viruses, and parasites) that contaminate the water.
• Public Health: If humans consume or come into contact with water contaminated by these pollutants and the associated pathogens, it leads to the spread of waterborne diseases like cholera, typhoid, and dysentery.

3. Show the Solution

• Option A (Air pollution): While some decomposition can release gases, it is not the primary reason these pollutants are considered "unsafe" in water systems.
• Option B (Soil degradation): This relates more to land pollution than the specific impact of water-based biodegradable pollutants.
• Option C (Ill health): Because biodegradable pollutants encourage the growth of pathogens and deplete oxygen, they make water unsafe for drinking and domestic use, directly leading to diseases and ill health in humans.
• Option D (Greenhouse effect): This is primarily caused by gases like $CO_2$ and methane in the atmosphere, not by the presence of biodegradable matter in water.

4. Identify the Answer

The most significant danger posed by biodegradable pollutants in water systems is the contamination of water sources, which leads to the spread of diseases. Therefore, they cause ill health.

5. Tip

When you see questions about "biodegradable pollutants in water," always link them to Biochemical Oxygen Demand (BOD) and waterborne diseases. If the water is polluted, the immediate threat to humans is the health risk!