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ASTM D6691 - Aerobic Biodegradability of Plastics in Seawater - CO2 Evolution (ISO/IEC 17025:2017 Certified)

ASTM D6691 is an aqueous aerobic biodegradability test that determines the degree and rate of aerobic biodegradation of plastic materials in seawater by measuring CO2 evolution. This test relies on the pre-grown population of at least ten aerobic marine microorganisms of known genera or the indigenous population existing in natural seawater. The test method is conducted under controlled laboratory conditions.

This test method is applicable to all polymer materials containing at least 20% carbon that are not inhibitory to the microorganisms present in a marine environment. 

The test normally lasts for 10-90 days, but it is acceptable for the experiment to be
terminated in advance when cumulative CO2 production plateaus or extended if no biodegradation has occurred in a specific time.

CONCEPT AND PRINCIPLE

ASTM D6691 IS an aqueous aerobic biodegradability test that determines the degree and rate of aerobic biodegradation of plastic materials in seawater.

Biodegradation is followed by measuring the evolution of CO2 using a suitable, analytical method. The level of biodegradation is determined by comparing the amount of CO2 evolved with the theoretical amount of evolved CO2 (ThCO2) and expressed in percentage. The test result is the maximum level of biodegradation, determined from the plateau phase of the biodegradation curve. 

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ASTM D6691

ASTM D6691 Key Summary

▶ Materials that can be tested:
     ➢ All polymer materials containing at least 20% carbon that are not inhibitory to the microorganisms present in a marine environment at the test dosage.
▶ Test substance requirement:
     ➢ The total organic carbon (C%) needs to be known in order to calculate the ThCO2;
     ➢ Test specimens in the form of powders shall be characterized as to particle size distribution. Mean particle size less than 25 mm is recommended;
     ➢ Materials which, under the test conditions, do not inhibit the microorganisms present in the working solution.
▶ Temperature: 30 ± 2°C.
▶ Reference: a well-defined biodegradable polymer (e.g., cellulose, chitin or Kraft paper, or all three).
▶ Test substance dosage: 20 mg of test substance per reactor (125 mL).
▶ Number of reactors: 3 for blank control, 3 for reference control, and 3 for test substance.
▶ Extra control: Sodium bicarbonate (100 mg) and sodium sulfite (100 mg) in an acidic water solution (100 mL) to check the CO2 measurement accuracy.
▶ Duration: normally 10-90 days, but it is acceptable for the experiment to be terminated in advance when cumulative CO2 production plateaus or extended if no biodegradation has occurred in a specific time.

Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ASTM D6691. 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
ASTM D6691CO2 evolutionOrganic carbon content *+-+

*"Sample info required" is the information needed to calculate the biodegradation percentages. This must be available for a selected method.
*"Organic carbon content" is the ratio of the organic carbon weight to the weight of the sample. It can be calculated by the sample formula (e.g., acetic acid C2H4O2, carbon content is 12*2/(12*2+1*4+16*2)=40%). Try our Online C% Calculator. If the formula is unknown, we can send the sample out to a third party lab for you for analysis (normally $110 with a 10-day turnaround time).

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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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