Biodegradability of Cellulose Diacetate in Aqueous Environments

Cellulose acetate with a degree of substitution (DS) of 2.5, commonly referred to as cellulose diacetate, has been discussed as an important source of microplastic in the environment, especially since it is used to produce cigarette filters. According to EU Single-Use Plastics Directive tobacco products are one of the ten most found SUP products in beach litter by number. However, at present only very few biodegradation studies with natural microbial communities in aqueous media have been reported. In the present study aqueous aerobic biodegradation simulation tests were performed on commercial materials according to international standards (ASTM D6691, ISO 14851 and ISO 19679) to address this bias. Cellulose diacetate proved to be biodegradable or showed strong indication to be non-persistent in freshwater (> 90% relative biodegradation after 100 days at 21 °C), seawater (> 90% after 142 days at 30 °C) and seawater/sediment interface (> 70% after 360 days at 25 °C) under defined laboratory conditions. In freshwater, biodegradation of cellulose diacetate was characterized by a prolonged lag phase (75 days), followed by > 90% relative biodegradation in a short time frame (25 days). This indicates that an abiotic degradation or hydrolysis to reduce the DS is not a pre-requisite to initiate the biodegradation of cellulose diacetate. In addition, it was found that the lag phase can be significantly shortened (from 75 to 5 days) by using pre-adapted microorganisms. In contrast to what could have been expected from literature our present study demonstrates that microorganisms can adapt to a DS as high as 2.5 and metabolize the material. This underlines the importance of studies with natural communities of microorganisms to get a more realistic idea of the persistence of a polymer material.