Which concept describes substances that deplete dissolved oxygen in aquatic environments?

• A. Plant Nutrients
• B. Organic Chemicals
• C. Oxygen-Demanding Wastes
• D. Inorganic Chemicals

Answer: (C)

Oxygen-demanding wastes describe substances that deplete dissolved oxygen in aquatic environments. These are biodegradable organic materials—such as sewage, food waste, and animal manure—that microbes break down. As microorganisms metabolize this organic matter, they use dissolved oxygen for respiration, which lowers the oxygen levels in the water. This can lead to hypoxic conditions that stress or kill aquatic life. Water quality terms like biochemical oxygen demand (BOD) quantify this effect by estimating how much oxygen would be consumed as the waste decomposes. While plant nutrients can drive processes (like algal blooms) that eventually affect oxygen, the direct concept of depleting dissolved oxygen is best captured by oxygen-demanding wastes.