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Biological oxygen demand (BOD) (also called biochemical oxygen demand) refers to the amount of oxygen that would be consumed if all the organic materials in a one liter water sample were oxidized by bacteria and protozoa. The units are typically milligrams of oxygen per liter.
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BOD is good measure of the contamination level of a water supply. It is used primarily for waters that receive pollution from sewage and industrial wastes.
The first step in a BOD determination is taking a water sample from the test area and diluting it with a known volume of distilled water. The solution is then thoroughly shaken to insure oxygen saturation. The amount of dissolved oxygen is determined and the sample is sealed and placed in darkness for five days so as not to stimulate algal growth. During this five day incubation period, microorganisms in the sample will decompose the organic materials and consume oxygen in the process. The dissolved oxygen is then measured again. The difference between the initial and final readings is directly proportional to the amount of organic material in the original sample. BOD's are generally expressed as milligrams of dissolved oxygen per liter, which is equivalent to parts per million, PPM.
BOD levels can vary considerably. Pristine water sources may show a BOD of less than 2 mg/L of water. Raw sewage typically has BOD readings in the hundreds of mg/L and food-processing wastes may be in the thousands of mg/L.
Dissolved oxygen (DO) levels are crticially important to aquatic life. Aquatic systems with high BOD's may have very low dissolved oxygen levels (2 to 4 mg/L DO versus 8 mg/L DO or healthy water bodies), particularly if there are no mechanisms for introducing oxygen such as waterfalls, dams, rapids etc. Low dissolved oxygen levels can cause (or be a major contributing factor) to fish kills and "dead zones".
Section 12 of SDS's that conform to OSHA's implementation of the Globally Harmonized System (GHS) in the HCS 2012 regulation may list the environmental fate of the material and involve discussion of how the material affects BOD. However, while SDS's are required to contain Sections 12 through 15, OSHA does not have the rulemaking authority to require manufacturers to provide content for those sections and they are deemed "non-mandatory". Therefore, Section 12 is blank on many SDS's although many conscientious SDS authors will provide whatever information they can.
When BOD may appears on an SDS it is usually used to indicate how readily the material is decomposed by naturally occurring microorganisms. Ecological information may be required SDS content in countries other than the US.
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See also: Decomposition, hypoxia.
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