Samples can degrade significantly during extended storage.
If a sample is refrigerated prior to analysis, allow the sample to warm to 20 C before starting the test. A sample may be removed from an ice chest or refrigerator during transit to allow it to warm to 20 C before analysis begins. It is optimum to start the BOD 5 analysis immediately after sample collection to minimize changes in bacterial concentration. The maximum holding time of a sample to be analyzed for BOD is 24 hours. Never freeze samples.