Aerobic biodegradability of plastic materials exposed to seawater
According to ISO 23977-2, the determination of aerobic biodegradation of plastic materials exposed to seawater can be performed by measuring the oxygen consumption or depletion caused by aerobic respiration of microorganisms from seawater or seawater with low amount of sediment using Gas Endeavour® as a fully automated closed respirometer. During biodegradation of plastic materials, the consumed oxygen is measured continuously by Gas Endeavour® and the biodegradability is calculated as the ratio of the consumed oxygen to the theoretical value. The experimental configuration using Gas Endeavour® includes oxygen supply and the biodegradation process is not inhibited by the limitation of available oxygen in the headspace of test flask. It is therefore convenience to perform the analysis with a higher sample amount.
The figure displays the ongoing biodegradation over 110 days of incubation with continuous agitation at a temperature of 22 ±1 oC. The test period typically does not exceed 1 year and is considered valid if the degree of cellulose reaches at least 60% after 180 days. In the current study, the biodegradation of cellulose in seawater is only 9% ±4% after 110 days, whereas higher biodegradation rates of 43% ±8% (higher sample concentration) and 63% ±5% (lower sample concentration) can be observed for tests in seawater and marine sediment, respectively. These results clearly illustrate a lower degree of biodegradation in seawater only, due to the lower microbial density in seawater compared to a higher microbial density in sediment.