## 3 The Occurrence and Sources of Microplastics and Nanoplastics in the Environment
Thus, MPs may enter the human body commonly through endocytosis and persorption. The toxic chemicals are absorbed and accumulated on the surface of MPs and NPs, and their biomagnification poses a new risk to the biosphere in the long run [48]. Wastewater sludge, organic fertilizers, and agricultural plastic mulch films are some of the dominant sources of MPs and NPs in the environment [49]. However, many MPs and NPs derived from effluent discharge and agricultural activities pass through freshwater ecosystems, such as urban wetlands and natural rivers, to complete land-sea transport. As transition zones for substance exchange between terrestrial and aquatic ecosystems, wetlands may be essential in the environmental migration processes of MPs [50]. Figure 2: Plastic morphology. Evidently, MPs and NPs were observed in wetlands. For instance, analysis of sediment samples collected from 20 urban wetlands in Australia showed that MPs were observed at all wetlands with an average abundance of 46 particles/kg of dry sediment while plastic fragments accounted for 68.5% of all MPs found [50]. Another study conducted on coastal mangrove wetlands in China indicated that the abundance of MPs in mangrove sediment ranges between 8.3 and 5738 particles/kg with different MPs shapes including fibers, films, fragments, foams, and pellets [51]. It was concluded that the areas with intense human activity such as tourism, harbor transportation, and fisheries, and with dense vegetation intercept more MPs. In different areas of the Yellow River Delta wetland, MPs abundances ranged from 136 to 2060 particles/kg, where concentrations of PET ranged from 536 to 660 ug/kg, and the concentrations of polycarbonate (PC) ranged from 83.9 to 196 ug/kg [52]. This indicates that coastal wetlands are particularly at risk in trapping plastic waste since they are at the interface of terrestrial and marine systems and tidal wetlands are subject to plastic waste deposition, as they are within the vicinity of highly dense human population areas and activities. Furthermore, PE MPs with sizes ranging from 0.96 to 1.57 mm were detected in some fish species common in the Arabian Gulf [53]. A study on MP pollution was carried out in Kuwait, which included analyzing 44 intertidal locations and 87 fish and mussels' gastrointestinal contents. The findings revealed that only a few MPs were detected in about 15 locations, but three pieces of MPs were detected in the gastrointestinal tract of the grouper of fish (locally known as Hamour); and the identified MPs were mainly PP, PE, and PS [54]. [PERSON] et al., have reported that MPs concentration is highest in northern shores of the Arabian Gulf [55]. A study by [PERSON] et al. conducted in 2020 indicated that 50% of the global wastewater influent remains untreated, which adds about 3.85 \(\times\) 10\({}^{16}\) MPs annually to the aquatic environments [56]. The study concluded that treating all produced wastewater before its release could lead to a 90% decrease in the current MPs input into aquatic systems. MNPs are characterized by their persistence and accumulation in the environment. Thus, MNPs pollution negatively impacts the entire environment by contaminating the air, land, and water due to inadequate plastic waste management infrastructure, posing a threat to ecosystems and human health. MNPs change soil properties, harming biodiversity, and plant health. Wastewater effluent and sludge often contain significant quantities of plastic; thus, improper handling of plastic waste can cause plastic to enter terrestrial ecosystems, either directly or indirectly. Consequently, plastics can enter water and soil when effluent and sludge are used as fertilizer. As a result, water resources will be impacted.