2005-05 Dissolved Oxygen

Dissolved Oxygen (D.O.) is a physical analysis that refers to the volume of oxygen in a body of water. Oxygen can enter the water through absorption or plant photosynthesis. If D.O. levels are too low, there may be an adverse effect on plant and animal life existing in the water. It is therefore essential to attain an accurate measurement.

This test can be performed either at the laboratory or in the field. As D.O. levels can change and vary according to the time of day, weather and temperature, it is recommended that the analysis be performed as close to the time of sampling as possible.

Gas solubility increases as temperatures decrease (cold water can hold more oxygen.) It is therefore important to recognize that results may change with an inevitable change in temperature as samples are transported from the source. D.O. concentrations will also vary with pressure and agitation. If the sample is pressurized (e.g. in the cargo compartment of an airplane) or subject to excess shaking, the level of oxygen again may vary.

If you do not have access to appropriate D.O. instrumentation, you will find that many manufacturers and distributors have rental units available. In Western Canada, for instance, a D.O. meter can be rented from any one of a number of local companies specializing in field sampling and analysis equipment. There are different varieties available each with varying capabilities (and price.) Many of the newer portable D.O. meters are also capable of providing near instantaneous indications of both temperature and pH.

For more information on D.O. analyses, please refer to "Standard Methods for the Examination of Water and Wastewater," published by the American Public Health Association, or contact your local laboratory representative.