Field and mesocosm test methods to assess the performance of biodegradable plastic under marine conditions

The pollution of the natural environment, especially the world9s oceans, with conventional plastic is of major concern. Biodegradable plastics are an emerging market bringing along potential chances and risks. The fate of these materials in the environment and their possible effects on organisms and ecosystems has rarely been studied systematically and is not well understood. For the marine environment, reliable field test methods and standards for assessing and certifying biodegradation are lacking. In this work we present newly developed field tests to assess the performance of biodegradable plastics under natural marine conditions. These methods were successfully applied and validated in three coastal habitats (eulittoral, benthic and pelagic) and in two climate zones (Mediterranean Sea and tropical SE Asia). Additionally, a stand-alone mesocosm test system which integrated all three habitats in one technical system at 400-L scale independent from running seawater is presented as a methodological bridge. Films of the positive control test material polyhydroxyalkanoate copolymer (PHA) and the negative control low density polyethylene (LD-PE) were used to validate the systems. While LD-PE remained intact, PHA disintegrated with speed depending on the habitat and the climate zone. Together with the existing laboratory standard test methods, the field and mesocosm test systems presented in this work provide a 3-tier testing scheme for the reliable assessment of biodegradation of (biodegradable) plastic in the marine environment. This toolset of tests could be adapted to other aquatic ecosystems.