According to ISO 17556, the determination of ultimate aerobic biodegradability in soil can be performed by measuring the oxygen consumption or depletion caused by aerobic respiration of microorganisms using BPC Blue as a fully automated closed respirometer. The plastic materials, which is the sole source of carbon and energy, is mixed with the selected soil and incubated at temperature 22 ±1 ^oC. During biodegradation of plastic materials, the consumed oxygen is measured continuously by BPC Blue and the biodegradability is calculated as the ratio of the consumed oxygen to the theoretical value.

The low standard deviations can be observed for the cumulative oxygen consumption of both blanks and samples (lower than ±4% and ±9%, respectively). This supports a high level of confidence of the results obtained with BPC Blue. Accordingly, the validity criteria of ISO 17556:2019 are fulfilled (i.e., the positive control reached 60% biodegradation and BOD values of all blanks are within ±20%) and the PHB test material reached a 95% of biodegradation in 90 days.