Microplastics Overview: Types and Sources
At first, the term “microplastics” was used for the plastic matters in the range of 20 pm . But later, this range was widened in the range of smaller than 5 mm  with the upper limit of 1 mm (1000 pm), stated by . However, microplastics (MPs) are commonly defined as plastic particles having the size less than 5 mm [11-13]. This chapter concerns primarily the presence of MPs in freshwater bodies and its impacts on fishes. Research efforts on the accumulation and impacts in the freshwater system are very much less than the marine and terrestrial systems [14,15]. The concentration of MPs is constantly increasing in the aquatic environment owing to a tremendous increase in the production of plastics, with a total global production of 335 million tonnes in 2016 . Most of the authors have concluded that the primary sources of MPs are effluents from wastewater treatment plants (WWTPs), sewage sludge, shipping activities, atmospheric fallouts, direct disposal from the public, beach littering and runoffs from agricultural, recreational and urban areas (Figure 12.1).
Although the data are so far unavailable, the runoffs from industrial plastic production sites can be taken as an additional source. The products such as facial scrubs have been identified as a potential source of MPs in water bodies. A study shows that the size range
FIGURE 12.1 Origin of microplastics.
of four personal-care and cosmetic product wastes were in the range of 63-125 pm, 125- 250 pm, 250-500 pm and 500-2000 pm . Generally, MPs are classified as primary or secondary on the basis of their production.
Primary MPs are the ones having size <5 mm and mainly are originated from textiles, medicines, toothpaste and variety of other personal-care products like facial products and scrubs [17,18]. The range of primary MPs and their types mainly consists of fragments , fibers , films and foams . Secondary MPs can be originated by the fragmentation of big plastic materials degradation. They are derived from the degradation of larger plastic debris through mechanical forces, thermal degradation, photolysis, thermo-oxidation and biodegradation processes , for example, synthetic fibers from washing clothes . Secondary MPs arising by washing clothes are generally polyester, acrylic, and polyamide, which can be more than 100 fibers/L of effluent [21,22] (Figures 12.2 and 12.3).