Which of the following is NOT typically measured in a BOD test?

In a Biochemical Oxygen Demand (BOD) test, the primary focus is on measuring the amount of oxygen consumed by microorganisms as they decompose organic matter in water over a specified incubation period, typically five days at 20 degrees Celsius. This measurement serves to indicate the degree of organic pollution in the water sample, allowing for an assessment of water quality.

The presence of heavy metals, however, is not something that is typically measured in a BOD test. Heavy metals are inorganic pollutants that do not biodegrade in the same manner as organic materials. Instead, testing for heavy metals usually involves specific analytical techniques that focus on their chemical presence and concentration, which are distinct from the biological processes evaluated in a BOD test. Thus, the correct answer highlights that heavy metals are outside the scope of what is usually assessed in this type of analysis.