The substitution of conventional materials by biodegradable plastic is a possible countermeasure against the accumulation of plastic in the environment. Biodegradability of a material should be proven as part of a risk assessment. The actual degradation speed of these materials depends on the environmental settings, which include the concentration of enzymes, microorganisms, temperature, pH, humidity and oxygen and light availability. Most of the seafloor is covered with sediment. Sediment properties as permeability, oxygenation and nutrient content directly or indirectly depend on the grain size, as do the microbial community and the biogeochemical processes linked to it. To gain more insight into the effects of different sediments on the degradation rates of biodegradable plastic, we performed two iterative tank experiments. In a pilot study, marine sediment from one location was divided into four grain size fractions. In a follow-up experiment, sediment was collected from four different locations. Plastic disintegration was tested for a commercially available biodegradable plastic film (Mater-Bi HF03V), LDPE as a negative control and polyhydroxyalkanoate copolymer (PHA) as a positive control. In the pilot experiment, it was shown that disintegration rates of biodegradable plastic films were inversely correlated with grain size. Fastest rates were measured for mud, followed by fine to medium-fine sand (63 - 500 µm) and lastly the coarse (500 -