# Microbial and Enzymatic Biodegradation of Plastic Waste for a Circular Economy
## 1 Introduction  
Plastics have become an integral part of modern life due to their beneficial characteristics, including their versatility, light weight, durability, transparency, and chemical resistance. However, it is because of these characteristics that they have become inexpensive, disposable, and significant contributors to environmental damage [1]. The global production of plastics reached 460 million tons in 2022, with China and the European Union accounting for 32% and 17% of the world's synthetic plastic use, ranking first and second, respectively [2]. Synthetic plastics are polymers derived from chains of repeating monomers usually obtained from petrochemicals. Polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET), and polyurethane (PU) are examples of common synthetic polymers [3]. Each type of plastic has unique qualities which make it useful in a wide variety of applications, including packaging, home goods, and automobile parts. Table 1 shows different types of synthetic plastics, their structures and their applications. Plastics are widely used because of their versatility and efficiency, yet they have become one of the most pressing environmental concerns. The paradox lies in the fact that while plastics are useful and efficient materials, they have a durability that is misaligned with a material that is often designed for a single use, with its disposal becoming a significant threat to ecosystems, including land, marine, air, and water [2]. Studies have concluded that plastics and microplastics (plastic fragments less than 5 mm in size) can enter the human body through different means such as inhalation, ingestion, and dermal contact [10]. Long-term exposure can cause negative effects on human DNA and increase the risk of infertility and cancer [11; 12]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **Structure** & **Uses** & **Reference** \\ \hline Polyethylene (PE) & & & Shopping bags, drinks bottles, food packaging material, plastic pipes. & [4] \\ \hline Polyvinyl chloride (PVC) & & & Raincoats, shower curtains, window frames, indoor plumbing. & [4] \\ \hline Polypropylene (PP) & & & Manufacturing chemical derivatives, packaging, automotive industries. & [5; 6] \\ \hline Polystyrene (PS) & & & Disposable cups, packaging materials, laboratory consumables, electronic instruments. & [7] \\ \hline Polyethylene (PET) & & & Food and beverage packaging, photographic film, insulated clothing. & [8] \\ \hline Polyurethane (PU) & & & Plastic foams, cushions, rubber goods, synthetic heathers, adhesives, paints, fibres. & [9] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The most common types of synthetic plastic and their structures and common uses. Approximately 460 million tons of plastic waste were generated globally in 2022 [13]. This includes various types of plastics, with PE, PP, and PET being the most concerning ones. These plastics are commonly used in household items such as bottles, containers, shopping bags, and wrappers. They are often found in the environment, contributing significantly to pollution [14]. For example, low-density polyethylene (LDPE) and bioplastics such as PLAs and PHAs are commonly used in plastic bags, while synthetic plastics like PET are widely used in textiles and as food containers [15]. Single use plastic waste for items such as food and drink products accumulates more quickly than waste from durable and expensive materials like laptops, televisions, and automotive parts [16; 17]. Furthermore, such plastics are challenging to recycle due to their mixed nature. Only by using cleaned, non-mixed plastic can high-quality recycled products be produced [18]. Figure 1 shows how plastic management varies in the major world economies, with significant disparities in recycling, incimation, and mismanagement rates globally.