Aerobic Biodegradation Testing of Materials Using a Natural Marine Seawater Inoculum and Closed Loop Respirometer

Proper assessment of biodegradable materials depends on the wide adoption of standard test methods. Although such methods exist, testing capacity remains limited, constrained by cost and the start-up time to establish new laboratories. This modified screening protocol is based on the ASTM International D6691-24a, Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water Inoculum. It assesses the biodegradation of materials in a marine environment, comparing results to positive and negative controls, and uses a natural seawater inoculum supplemented with ammonium and phosphate to prevent nutrient limitation. Materials are exposed to this nutrient-enriched seawater and incubated at 30 °C. A Micro-Oxymax respirometer measures the production of biogas (carbon dioxide, CO2) over time. The degree of mineralization (biodegradation) is determined by calculating the proportion of material-derived carbon converted to biogas-carbon. The percent CO2 production, expressed as a fraction of the measured or theoretical carbon content, is reported as a function of time. The closed-loop respirometry system accommodates a range of reactor vessels, prepared in triplicate for each material, a negative control (seawater inoculum only), and a positive control (thin-layer chromatography cellulose). This method is important for evaluating materials in the marine environment and addresses global pollution prevention.