Which statement best describes the purpose of the Chemical Oxygen Demand (COD) test?

• A. A test that directly measures dissolved oxygen.
• B. A test used to indirectly measure the amount of organic compounds in water.
• C. A test to measure turbidity.
• D. A test to measure salinity.

Answer: (B)

The key idea is that COD is a chemical way to estimate how much organic pollution is in water, not by measuring the organics directly, but by how much oxygen would be consumed to oxidize them chemically. In practice, a strong oxidant under acidic conditions breaks down the organic matter, and the amount of oxygen equivalent used up is reported as COD. This makes it an indirect, rapid measure of the organic load in a sample, which is why it’s widely used for wastewater and industrial effluents. It’s not a direct measurement of dissolved oxygen in the water—that’s a separate test—nor does it assess turbidity or salinity. COD is valued for giving a fast, overall estimate of organic pollution, even though it can respond to some inorganic oxidizable substances as well.