It is the amount of oxygen consumed when decomposing (oxidizing) organic matter in water.
It is an index to measure the degree of pollution.

( Chemical Oxygen Demand)

It is used to measure the degree of pollution in seas, lakes and marshes.
Measures the amount of oxygen consumed to oxidize contaminants contained in water.
It is common to measure with chromium or manganese.

(Biochemical Oxygen Demand)

It is used to measure the degree of pollution of rivers.
Measures the amount of oxygen consumed to oxidize contaminants contained in water.
It is common to measure bacteria.

Seas, lakes, marshes, and other waters have remained in the same place for a long time, so
they contain a lot of phytoplankton.
Therefore, BOD measurements are not suitable for such locations.