Q. Biological Oxygen Demand (BOD) is a standard criterion for (UPSC Prelims 2017)
Answer:
Pollution assay in aquatic ecosystems
Notes: The correct answer is
[C] Pollution assay in aquatic ecosystems.
Biological Oxygen Demand (BOD) is a critical environmental index used to determine the organic wing of a water body. Here is why it is the standard for aquatic pollution:
- Mechanism: BOD measures the amount of dissolved oxygen needed by aerobic biological organisms (like bacteria) to break down organic material present in a given water sample at a certain temperature over a specific period.
- The Correlation: * High BOD indicates a high level of organic pollution (such as sewage or agricultural runoff). As bacteria consume the organic waste, they use up the oxygen, leaving less for fish and other aquatic life.
- Low BOD indicates that the water is relatively pure or has very little organic matter to be decomposed.
- The "Assay" (Test): It is a "pollution assay" because it doesn't just measure the presence of a chemical; it measures the impact that chemical/waste has on the oxygen levels of the ecosystem.
Key Differences to Note:
| Term | Definition |
| Dissolved Oxygen (DO) | The actual amount of free oxygen available in the water. High DO is generally healthy. |
| BOD | The "demand" for oxygen. High BOD is generally a sign of high pollution. |
| COD (Chemical Oxygen Demand) | A faster test that measures the oxygen required to chemically oxidize both organic and inorganic matter. COD is usually higher than BOD. |
Why other options are incorrect:
- [A] Blood Oxygen: This is measured using a pulse oximeter or arterial blood gas (ABG) test, not BOD.
- [B] Forest Ecosystems: Oxygen levels here are typically measured through atmospheric sensors focusing on photosynthesis-respiration cycles.
- [D] High Altitude: Oxygen levels in the atmosphere are measured by partial pressure (pO2) using barometers and specialized gas sensors.