Polypropylene structure alterations after 5 years of natural degradation in a waste landfill

Up to 25% of plastic waste in Europe is still disposed of in landfills, despite recycling efforts. The plastic waste in the landfill plot may be exposed both to abiotic and biotic degradation processes, although it is thought that most of the plastic materials tend to be resistant to biodegradation or biodeterioration even after a long time. To verify if polypropylene (PP) can undergo the process of short-term biodegradation and how this process is manifested in a municipal waste landfill, we collected a plastic sample from an already closed landfill plot estimating its age at approximately 5 years. Fourier-Transform Infrared Spectroscopy led to sample identification as PP as well as showed additional bands which are not specific to polymer structure but rather result from microbial metabolism. Differential Scanning Calorimetry was performed to examine the influence of the environmental degradation process on the degree of crystallisation of the tested PP. Moreover, significant changes on the surface of an old PP packaging were observed with Scanning Electron Microscopy (SEM) showing clear signs of PP delamination which resulted in microplastic particles formation (smaller than 5 μm in diameter). Additionally, several round and oval shaped structures were observed with SEM leading to the suspicion of biofilm formation on the PP surface. Indeed, the microorganisms were present in a vast amount on the old PP surface and possibly formed a viable biofilm as it was confirmed with fluorescence microscopy. These data show that plastic waste can be inhabited by microorganisms from the ambient environment which may probably lead to its faster degradation. However, this process should be investigated in more detail in order to shed light upon the possible risk factors of plastic biodegradation in waste landfills to the environment and human health. Even after five years, polypropylene can undergo deterioration/biodegradation in a waste landfill with viable microbial cells on its surface, possibly involved in its degradation.