Biological Degradation of Plastics and Microplastics: A Recent Perspective on Associated Mechanisms and Influencing Factors

Abstract

Plastic and microplastic pollution has caused a great deal of ecological problems because of its persistence and potential adverse effects on human health. The degradation of plastics through biological processes is of great significance for ecological health, therefore, the feasibility of plastic degradation by microorganisms has attracted a lot of attention. This study comprises a preliminary discussion on the biodegradation mechanism and the advantages and roles of different bacterial enzymes, such as PET hydrolase and PCL-cutinase, in the degradation of different polymers, such as PET and PCL, respectively. With a particular focus on their modes of action and potential enzymatic mechanisms, this review sums up studies on the biological degradation of plastics and microplastics related to mechanisms and influencing factors, along with their enzymes in enhancing the degradation of synthetic plastics in the process. In addition, biodegradation of plastic is also affected by plastic additives and plasticizers. Plasticizers and additives in the composition of plastics can cause harmful impacts. To further improve the degradation efficiency of polymers, various pretreatments to improve the efficiency of biodegradation, which can cause a significant reduction in toxic plastic pollution, were also preliminarily discussed here. The existing research and data show a large number of microorganisms involved in plastic biodegradation, though their specific mechanisms have not been thoroughly explored yet. Therefore, there is a significant potential for employing various bacterial strains for efficient degradation of plastics to improve human health and safety.

Keywords: biodegradation; enzymes; microorganism; microplastics; plastics; pretreatment.

Figure 1

Additives, dyes, and organic pollutants in plastics can have negative effects on both humans and nature.

Figure 2

Degradation pathways of microplastics. Plastic degrading to small fragments forming microplastics can enter cells after decomposition. It can be transformed into biomass for energy production or mineralized.

Figure 3

The enzymes involved in PET degradation secreted by Ideonella sakaiensis. Ideonella sakaiensis strain secretes enzymes PETase and MHETase, which degrade PET plastic, and the artificial enzyme PETase combined with MHETase significantly improve the degradation efficiency.

Figure 4

Pretreatment through physical and chemical methods can greatly make plastics prone to degradation.