The purpose of this standard is to specify a method for determining the biodegradability of nonionic surfactants used in the manufacture of detergent formulations. The method consists of two tests, which differ in their foundation and in the information they provide regarding the biodegradability of the product to be tested. The first test, called "static test" or "selection test", is carried out in a flask with continuous aeration by shaking ("open flask" type test). The second test, called "dynamic test" or "verification test", is based on a simulation of the conditions existing in wastewater treatment plants for biological treatment. The "static test" is used to make a first selection. Surfactants whose biodegradability, determined by this test, exceeds the minimum required percentage, are accepted as biodegradable. The test is simple and relatively quick, lasting a maximum of 19 days. It can be carried out simultaneously for several surfactants. The "dynamic test" is applied, as a verification test, to surfactants that have not been classified as biodegradable in the "static test". For these surfactants, the "dynamic test" is what is taken into consideration when determining their biodegradability. This test requires more complex equipment than the "static test" and usually lasts more than 30 days. Certain chemicals, present in aqueous media or in ambient air, can reduce, or even inhibit, the activity of the microorganisms that cause the biodegradation of non-ionic surfactants, delaying this process or influencing the final result. These products include strong alkalis, toxic metals, bactericides and organic solvents. Even surfactants themselves can inhibit the activity of microorganisms if they are present at sufficiently high concentrations.