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Analysis of the microplastic emission potential of a starch-based biodegradable plastic material
Summary
Researchers developed a method to assess the microplastic emission potential of biodegradable starch-based plastics under environmental conditions, finding that even materials labeled biodegradable can fragment into persistent microplastic particles depending on environmental degradation pathways.
This article describes a method for characterizing and classifying polymeric materials in terms of their potential to release persistent microplastics into the environment in the event of littering. When a polymeric product is released into the environment, it undergoes environmental degradation, which leads to the formation of microplastics. It is assumed that these microplastics add to the number of microplastics present in the environment and, therefore, represent an additional ecological hazard to the biota, for as long as they circulate in the environment. The greater the number of microplastics and the longer the residence time in the environment, the greater the chemical and physical risk to the biota. In order to quantify this hazard and classify the different materials, a parameter called microplastic emission potential (MPEP) is defined. The MPEP is the potential of a polymeric material to add persistent microplastics to the environmental pool. The term persistent indicates that the material's build up potential is taken into account. We have applied this parameter to cellulose (a natural polymer known to be biodegradable), HDPE (a conventional polymer known to be a source of persistent microplastics), and a biodegradable plastic material. The MPEP values of cellulose and of the biodegradable plastic material were equal, but that of HDPE was 1827 times higher. We also developed a model that considers the amount of microplastics present in the environment as the dynamic result of a fragmentation reaction (which creates microplastics) and a biodegradation reaction (which removes microplastics). Using the model it is possible to simulate the build-up of microplastics in the environment from different polymers (each characterized by its own fragmentation and biodegradation rates), or from the same polymer when exposed to specific environmental conditions that affect the degradation rates. This model, if validated, will be useful in assessing the environmental risk due to single-use items or packaging in the event of littering.