Which pollutant category is most associated with oxygen depletion in water due to decomposition?

• A. Major Water Pollutants
• B. Biodegradable Wastes
• C. Thermal Pollution
• D. Sediments

Answer: (B)

Oxygen depletion from decomposition happens when microbes break down organic material, using dissolved oxygen in the process. Biodegradable wastes are organic substances that microbes readily digest, so introducing them into water sharply increases the rate of oxygen consumption as they decompose. This raises the biochemical oxygen demand (BOD) and lowers the dissolved oxygen, leading to hypoxic conditions. That makes biodegradable wastes the pollutant category most closely tied to oxygen depletion due to decomposition.

Other choices don’t fit as directly: major water pollutants is a broad label, not the specific driver of oxygen loss via decay; thermal pollution changes DO mainly through temperature effects on oxygen solubility and microbial activity, not the decomposition of organic matter itself; sediments can influence DO indirectly but the primary link to oxygen debt from decay is the presence of biodegradable organic matter.