**2.1 Types of microplastics**

Microplastics are classified into two groups based on their origin: primary and secondary microplastics [27].

#### *2.1.1 Primary microplastics*

Primary microplastics are micro-sized synthetic polymers that are directly introduced into the environment as minute particles. They are utilized as exfoliates in a variety of operations, such as chemical compositions, abrasive media, chemical and petrochemical cleaning, and synthetic clothing manufacturing. They can be added voluntarily to items like cleaning agents in hygiene and cosmetics (e.g., shower gels). They can also be caused by the abrasion of big plastic objects during manufacturing, usage, or maintenance, such as tyre erosion, while driving or the abrasion of synthetic textiles during washing [28]. Microbeads are a form of primary plastic (size 2 mm) that is made up of polyethylene (PE), polypropylene (PP), and polystyrene (PS) beads and are used in cosmetic and health care goods [12].

#### *2.1.2 Secondary microplastics*

Secondary microplastics are microplastics that result from the decomposition of larger plastic products into microscopic plastic pieces in the marine ecosystem. This occurs as a result of ecological changes, such as microbial degradation, photocatalysis,

#### **Figure 2.**

*Classification of microplastic based on sources, size, type, and shape [29].*

high-temperature degradation, thermal decomposition, hydrolysis, and other weathering processes of indiscriminate dumping, such as abandoned plastic bags or unexpected losses, such as fishing gear. Microplastics in the waters can either circulate or sink. Microplastics that are lighter than seawater, such as polypropylene, will flow and spread across the oceans. They subsequently congregate in gyres formed by tidal currents (**Figure 2**) [28].
