**5. Risks of microplastic pollution in the aquatic ecosystem**

Plastics have really been recognized as a substantial component of marine plastic pollution for centuries, but their biological and environmental implications on marine ecosystems have only recently been emphasized and appreciated [16, 21]. Microplastics pose a great risk to aquatic life, as their small size makes them readily available to a wide range of marine organisms, and it is of increasing scientific concern (**Figure 4**) [13, 19–21, 34, 45].

Chemical toxins, indigestibility, choking dangers, and a channel for the spread of microbes are just a few of the potential risks that microplastics provide to organisms. These threats increase the risk to aquatic fish and human survival. In this section, we discussed the various risks microplastic pollution posed to the marine ecosystem.

*The Risks of Microplastic Pollution in the Aquatic Ecosystem DOI: http://dx.doi.org/10.5772/intechopen.108717*

**Figure 4.**

*The effect of microplastic pollution on marine ecosystem [58].*

#### **5.1 Chemical toxins**

Plastic's durability and corrosion resistance make it an appealing and preferable material to employ, but it also makes it very resistant to deterioration, making the dumping of plastic litter troublesome [45]. The composition of this plastic waste, as well as the enormous surface area of microplastics, makes them vulnerable to attaching watery organic contaminants and hazardous plasticizer leaching. Ingestion of microplastics may thus introduce toxins to the bottom of the food chain in the marine ecosystem, where toxic chemical buildup in the tissues of aquatic living species is possible [59].

Perhaps because plastics are commonly considered to be biochemically inert [59, 60], plastic additives, also known as "plasticizers," may be fully integrated into plastics during manufacturing and injection molding to improve their properties or extend their life by providing resistance to heat (e.g., polybrominated diphenyl ethers), oxidative damage (e.g., nonylphenol), and antimicrobials (triclosan) [37, 61]. These additives are harmful to the environment and the marine ecosystem. Because they both prolong the decomposition time-frames of plastic and may seep out potentially hazardous chemicals into marine aquatic life [45, 62, 63].

A few of these chemicals can move away from the synthetic matrix of plastic due to inadequate polymerization of polymers during manufacture. The extent to which these additives leak from polymers is determined by the pore size of the polymer matrix, which varies by polymer, the additive's size and characteristics, and environmental circumstances, such as weathering [16, 19, 59]. Because microplastics have a high surface-area-to-volume ratio, live species in the marine ecosystem may be directly exposed to leached additives after ingesting microplastics. These chemicals and monomers have the potential to disrupt biologically vital processes, perhaps leading to endocrine disruption, which can have an impact on movement, reproduction and development, and carcinogenesis [45, 62, 64].

Polybrominated diphenyl ethers, phthalates, and the component monomer bisphenol A are well-known endocrine disruptors because they can mimic, compete with, or alter the synthesis of natural hormones [63]. Chemical imbalance can result in temporary or permanent morphological changes in aquatic creatures during their formative phases, as well as sexual disruption in adults. In aquatic invertebrates and fish, phthalates have been related to a variety of molecular and whole-organism consequences, including genotoxic damage (micronuclei and death in mussel hemocytes), restricted motility in invertebrates, and intersex abnormalities in fish [65].

#### **5.2 Indigestibility**

While larger forms of garbage are easier to remove from a beach, microplastics are more challenging to eliminate but appear less apparent. Microplastics, due to their microscopic size, have the potential to be consumed by a variety of marine biota [15, 66]. Microplastic consumption in the wild is difficult to observe methodologically [67], however, an increasing number of studies are reporting microplastic ingestion across the food chain. The marine ecological danger associated with microplastics is the increased likelihood of ingestion by animals, such as birds, fish, and invertebrates, resulting in diminished foraging capacity and feeding stimulation, nutritional loss, and gastrointestinal issues [22, 68].

Microplastics pose a significant risk to aquatic life due to their small size, which makes them easily accessible to a wide range of marine creatures, and it is a growing scientific concern [13, 18–21, 31]. In addition to the possible negative effects of swallowing microplastics, toxic responses could emerge from endogenous pollutants leaking from the microplastics and external pollutants adhering to and trying to disassociate from the microplastics. Moreover, utilizing fluorescent nanospheres, phagocytic uptake of nanoplastics in a heterotrophic ciliate was observed. These lower-trophic level creatures are especially susceptible to swallowing microplastics since many of them are indiscriminate feeders with poor ability to distinguish between plastic particles and food particles [16]. As a result, microplastics will be widely and easily available to a wide range of planktonic creatures, including the larval stages of a number of industrially useful species found in the euphotic zone [13, 38]. This interaction between plankton and microplastics is theoretically amplified in gyres, where plankton numbers are low and microplastic intakes are high due to plastic deposition by ocean currents [16].

Microplastics can be consumed by a variety of marine living animals, including seabirds, crustaceans, and fish [69, 70]. Microplastics were found in the intestines of 35% of the planktivorous mesopelagic fish dissected in the north Pacific central gyre [71]. Plastic fibers, pieces, and coatings were also discovered in 13 of 141 mesopelagic fish captured in the north Pacific gyre [72]. In total, 83% of Nephrops sp. sampled in the Clyde sea (Scotland) had consumed pollutants. This economically useful, omnivorous, benthic crustacean primarily ate portions of monofilament line, and plastic bag shards [73].

Plastic fibers in the ecosystem can be as small as one nanometer in diameter and 15 nanometers in length, making them easily accessible to minute planktonic species [74]. Such fibers may be particularly hazardous as they may clump and knot, potentially preventing egestion [73]. In all of the preceding situations, the marine species may have consumed the microplastics intentionally, mistaking them for prey or food. It is yet to be determined whether the consumption of non-polluted microplastics has any substantial detrimental health impacts on biota, such as sickness, death, or reproductive success [75]. Once eaten, microplastics may pose a mechanical hazard to tiny animals, comparable to the consequences reported with macroplastics and bigger species [13, 45].

#### **5.3 Channels for the spread of microbes and adhered pollutants**

Marine plastic pollutants, particularly microplastics, are vulnerable to contamination from a variety of waterborne contaminants, including aqueous metals [15, 27], produce harmful chemicals [19], and persistent organic pollutants (POPs), also known as hydrophobic organic contaminants (HOCs) [57]. Such compounds are typically found in the highest quantities in the sea-surface microlayer, which also contains the largest concentrations of low-density microplastics [19, 57, 59].

Under optimal circumstances, phenanthrene was more likely to stick to plastics than to sediments. However, if heavily polluted microplastics come into interaction with non-contaminated sediments, the deposition differential would allow phenanthrene desorption to organic materials in the sediment [5]. A variety of contaminants, including PCBs, PAHs, DDTs and their metabolites, PBDEs, and bisphenol A, were found adhering to the surface of plastic pieces (less than 10 mm) tested from pelagic and neritic stations [76].

Microplastic waste containing POPs may be carried across seas, damaging marine ecosystems [77], or swallowed by marine creatures, transmitting poisons from the environment to aquatic life (i.e., a "Trojan horse" effect) [20, 38]. Many POPs are hazardous, causing endothelial dysfunction, mutagenesis, and/or cancer, and have the potential to biomagnify in higher-trophic organisms [5]. Ref. [78] came to a similar conclusion when they discovered that ingestion of plastic particles hampered the accumulation of fat deposits in migratory red phalaropes (Phalaropus fulicarius), affecting long-distance migration and possibly their reproductive effort on breeding places.

#### **5.4 Choking effect**

Plastic pieces and microplastics may also obstruct feeding tentacles and/or impede food transit through the digestive tract [70] or produce pseudo-satiation [the feeling of being full], resulting in reduced food consumption [21, 32]. However, [26, 32] argue that numerous marine organisms have the ability to eliminate foreign particles, such as sediment, natural decaying organic matter, and particulates from their bodies without harm, as illustrated by polychaete worms, which ingested microplastics from their surrounding sediment and then egested them in their fecal contamination casts [20].

Ingestion of plastics may cause blocking of stomach enzyme secretion, decreased eating stimulation, decreased steroid hormone balance, prolonged ovulation, and fertility problems in several marine animals [79]. Ingestion of plastic waste by small fish and seabirds, for example, can limit food intake, induce internal damage, and death due to intestinal infection [22, 23, 80]. Nonetheless, the magnitude of the injury will differ between species. Because of their inability to excrete ingested plastic material, Procellariiformes, for example, are more vulnerable [79, 81].
