Decomposable materials that consume oxygen are best described as which pollutant group?

• A. Nitrates and Phosphates
• B. Sediments
• C. Biodegradable Wastes
• D. Toxic Chemicals

Answer: (C)

Biochemical oxygen demand occurs when microorganisms decompose organic material and use dissolved oxygen to do so. Substances that are readily decomposable—biodegradable wastes—provide abundant food for these microbes, so they consume more oxygen in the water. If a body of water receives a large amount of biodegradable waste, the microbial activity can deplete oxygen faster than it can be replenished, leading to low dissolved oxygen and stressed or killed aquatic life. That’s why biodegradable wastes are described as the pollutant group that consumes oxygen.

Nitrates and phosphates are nutrients that can fuel algal blooms, which may later lead to oxygen depletion when the algae die and decompose, but they themselves are not the materials that directly consume oxygen. Sediments affect clarity and habitat, not the immediate oxygen demand. Toxic chemicals can harm organisms in various ways, but they aren’t defined by oxygen consumption in the same way.