ISO 9439 Key Summary
The ISO 9439 CO2 evolution method uses respirometry to determine the biodegradability by measuring the CO2 formation during the biodegradation process over 28 days. As the chemical decomposition process primarily result in the formation of CO2 and H2O, the measurement of generated CO2 can well reflect the biodegradation of the test compounds. With the measured and the theoretical CO2 amount, one can easily calculate the degradation percentages over a specified incubation time.
The aeration of the working solution requires the use of CO2-free air, which can be easily obtained by using a few NaOH washing bottles to remove all the CO2 present in the air. After that, CO2-free air can be sent to aerate the working solution.
During the aeration, CO2 is generated as a result of test substance biodegradation. Such CO2 can be easily stripped off the working solution during the aeration process. To capture it, three absorption bottles are usually used containing known amount of Ba(OH)2 to convert CO2 to BaCO3 precipitation. An afterwards acid-base titration using HCl as the titrant can determine the amount of the residual Ba(OH)2, which can be used to back calculate the amount of CO2 generated during the biodegradation.
Information on the toxicity of the test substance is helpful in determining the appropriate dosage so that the material does not inhibit bacteria at the concentration tested.
This method is appropriate for highly soluble, poorly soluble (or even insoluble) and/or absorbing materials. However, since aeration is performed throughout the incubation process, the test substance should not be volatile. ISO 9439 is similar to OECD 301B and ASTM D5864, and the common materials tested by these two methods include lubricants, grease, oil, fuels, surfactants, and personal care products.
