Occurrence of Microplastics
Plastics are undeniably a key component of our contemporary world, confronted every day at home, offices, grocery shops to the hospitals, schools and almost everywhere. However Fendell and Sewell, (2009) observed that unfortunately, over 50% large plastic items culminate in the oceans and over the course of time form macroplastic debris.
Global plastic production in 2017 according to Statistica (2017), was estimated at a whopping 348 million metric tonnes. This trend is still likely to rise as depicted in Figure 1.
Sources of Microplastics
Microplastics are defined as plastic fragments with the size of less than 5 mm. Browne et al., (2015) had however proposed that the definition should take into account smaller fragments as well (<1 mm). Their gradual degradability, ingestion by aquatic organisms and carriers of persistent organic pollutants from environment to aquatic organisms has become a major source of growing environmental concern.
Figure 2 illustrates the classification of microplastics based on shape, size and polymer type. Generally, microplastics in the marine environment are typically found as pellets, fragments, or fibers and are composed of diverse polymers (Smith et al., 2018, Galgani et al., 2013). Denser particles such as PVC, polyester, polyamide tend to settle at the bottom of the ocean bed while the lighter (polyethylene, polypropylene, and polystyrene) are found floating on the surface of the oceans.
Figure 2. Classification of microplastics based on shape, size and polymer type.
Mega debris fall in the 100 mm range while micro-debris is below 5 mm (Ryan et al., 2009; Thompson et al., 2009). Also, they are categorized based on their production. Primary microplastics are produced for direct consumption which is found in our everyday lives whereas the secondary microplastics occur as a result of the degradation of larger plastic molecules. Table 1 shows a compilation of the worldwide production of plastic polymers in million tonnes, estimated decomposition rate and recyclability. It reveals that production of LPDE (used in production of containers for milk, cleaning agents, shampoo, boxes) is 57 million tonnes yearly, closely followed by PP (55 million tonnes). However, a good reprieve is that they are recyclable and can be used for other things long after their primary uses are over. It is alarming to know that polyamide polymers take an estimated time of 600 years to degrade and is not recyclable.
Table 1. Worldwide production of polymers (million tonnes), estimated decomposition (years) time and recyclability
| Type of Microplastics Present | Production in Million Tonnes | Commercial Application | Estimated Time for Decomposition (yrs) | Recyclability |
| Polyamide (PA)/Nylon | 42 | Fishing nets and ropes, carpets, sportswear, textile | 600 | No |
| Polyvinyl chloride (PVC) | 15 | Film, Pipe, Insulation, roofing materials, | >450 | No |
| Polypropylene (PP), Polyterephthalate (PET), Polyester(PES) | 55
32 | Rope, bottle caps, gear. Strapping, bottles, boats, textiles | 450 | Yes |
| Polystyrene (PS) | 17 | Cool boxes, floats, cups, utensils, take away packs. | 50 | Rarely |
Polyethylene PE HPDE
LPDE | 40
57 | Plastic bags, storage, Containers for milk, cleaning agents, shampoo, boxes, straws, | 20 | Yes |
| Cellulose acetate(CA) | 11 | Cigarette butts | 10-12 | No |
Modified from: Enders et al.,2015, Geyer et al., 2017