Current life cycle analysis (LCA) methodologies lack indicators to assess the biodegradation of plastic materials introduced to the natural environment. If ending up in the sea, biodegradable plastics are assumed to be less persistent than conventional ones. However, reliable methods and data on the biodegradation of any plastic material in the ocean are not systematically available. We applied a 3-tier test scheme of reliable and environmentally relevant methods in laboratory, mesocosm and field tests to assess the biodegradation as well as the disintegration performance of several plastics including certified compostable materials under real environmental conditions in coastal habitats of Southern Europe and SE Asia. The mathematical modeling of the experimental results and the calculation of a specific half-life of a plastic material under specific environmental conditions show that the persistence is highly depending on where a certain plastic item is ending up. The specific half-life as a material property thus allows for the numerical comparison of different environmental scenarios and can be fed into LCA models.