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ISO 23977-2: Aerobic Biodegradability of Plastics in Seawater - Oxygen Consumption (ISO/IEC 17025:2017 Accredited)

ISO 23977-2 is a laboratory test guideline for determining the degree and rate of the aerobic biodegradation level of plastic materials. Biodegradation of plastic materials is determined by measuring the oxygen demand in a closed respirometer when exposed to seawater sampled from coastal areas under laboratory conditions.

The conditions described in this document might not always correspond to the optimum conditions for the maximum degree of biodegradation, however this test method is designed to give an indication of the potential biodegradability of plastic materials.

The test normally lasts for 1 year, but can be extended up to 2 years.


ISO 23977-2 determines the biodegradability of a plastic material by measuring oxygen consumption during the biodegradation process in a closed bottle setup (with head space). The degradation percentage is calculated as the ratio of oxygen consumption to the theoretical oxygen demand (ThOD).

This standard describes two variations of a test method for determining the biodegradability of plastic materials by the indigenous population of microorganisms in natural seawater using a static aqueous test system. The test is performed under mesophilic test conditions for up to two years by incubating plastic materials with either seawater only ("pelagic seawater test") or with seawater to which low amount of sediment has been added ("suspended sediment seawater test"), coming from the same site as that from which the seawater was taken.

The chemical formula of the test substance and its purity may be known to calculate the ThOD. The material is preferably in powder form with a maximum size of 250 um in diameter to provide better bioavailability for faster 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.

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ISO 23977-2

ISO 23977-2 Key Summary

▶ Materials that can be tested:
     ➢ Plastic materials.
▶ Test substance requirement:
     ➢ Formula needs to be known in order to calculate the ThOD;
     ➢ Preferably in powder form with maximum size of 250 um diameter;
     ➢ Similar shapes of different substances should be used if they are to be compared.
▶ Measurement: oxygen consumption (any type of respirometer is fine as long as the measurement is accurate).
▶ Temperature: 15-25°C.
▶ Reference: a well-defined biodegradable polymer (e.g., microcrystalline cellulose powder or ashless cellulose filters).
▶ Test substance dosage: at least 100 mg/L of the substance, or 170 mg/L of ThOD.
▶ Reactor example: 300 mL of volume with 90 mL of natural seawater only, or natural seawater with 0.1-1 g/L sediment.
▶ Number of reactors: 3 for blank control, 3 for reference control, and 3 for test substance.
▶ Duration: normally up to 1 year; prolong the test up to 2 years if significant biodegradation is still observed after 1 year.
▶ Upon termination, determine pH, nitrate and nitrite to correct the calculated degree of biodegradation for nitrification.

ISO 23977-2 Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 23977-2. Please check our Method Selection Guide to select the most appropriate method for your materials. You can also find the applicability for many other methods on Aropha Resource Center

TestAnalytical methodSample info required *Poorly solubleVolatileAdsorbing
ISO 23977-2Oxygen consumption
ThOD *

*"Sample info required" is the information needed to calculate the biodegradation percentages. This must be available for a selected method.
*"ThOD" can be easily calculated based on the formula of the sample. Try our Online ThOD Calculator.

Aropha Resource Center

To learn more about different types of biodegradation tests, their applicability, biodegradation mechanisms, and many other information such as case studies, publications, and blogs, please check our Aropha Resource Center

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