The carbon dioxide evolution test, also known as the modified
Sturm test, has (similarly to the OUR method) been established
and continuously updated for almost 3 decades [31]. The test was
designed for evaluating the biodegradability of non-volatile compounds
in liquid medium. The standard CO2 evolution test involves
aerating ameasured volume of sample and inoculum with CO2-free
air for 28 days; the CO2 produced was trapped in alkaline solution
and measured by titration. When this method is used as a toxicity
assay, an easily-biodegradable substrate is also added, and the ratio
of CO2 production with a toxicant in it to one without a toxicant can
be used as an indication of the degree of toxicity. Compared to an
OUR test, the CO2 evolution test features longer incubation times,
and thus, is more suitable as a biodegradability and chronic toxicity
assay.