# The Microplastics Cycle: An In-Depth Look at a Complex Topic
## 2 The Microplastics Cycle
### Microplastics in Oceans  
Much of the research on plastic pollution in marine systems has focused on ocean surface waters [91], but recent studies have expanded to examine microplastics at the ocean's depths, so existing knowledge disproportionally favors surface water. Approximately 18% of the plastic identified in marine habitats comes from fisheries and sectors associated with fishing [92]. The broad use of plastic items as direct replacements for metal and mechanical components in the fishing and allied industries is the primary factor for their prevalence in marine systems [93]. Additionally, aquaculture increases or introduces many plastics into the marine ecosystem [94]. Comparing wild and farm-raised or cultured mussels, for instance, the amount of microplastic debris in farmed mussels is substantially greater than that in mussels captured in the wild, away from the farming facilities. This rise in plastic debris in cultivated mussels is mostly due to the use of PP plastic lines in mussel farming [95]. Additionally, beach plastic litter is a significant contributor to plastics and microplastics entering marine habitats. Approximately 50 percent of beach litter is composed of plastic [96]. These plastics may either immediately enter the sea or ocean as plastics, or degrade on the beach and enter the marine ecosystem as microplastics. Vectors that contribute to the movement of microplastics into the marine environment include wind, rain, streams, and rivers, and also illegal waste dumping. Research on microplastics in marine settings has been widely published. We quantified this using the Web of Science Core Collection database to search through all 3616 publications that had been published up to 2022. The search strategy encompassed all permutations of the term'microplastics' in conjunction with each of the three related phrases: 'ocean','marine', and'sea' (Figure 4). Locations and published years were culled from the research. The data suggests that China is the global leader in publishing on the effects of microplastics on marine ecosystems, followed by the United States (Figure 3). Over the past five years, academic articles on microplastics in marine environments have surged to approximately four times their previous numbers. Micropplastics' age in the marine environment has a substantial bearing on their effects and problems [97]. As microplastics spend more time in the environment, the possibility that microorganisms, invertebrates, and vertebrates they interact with, grows [98; 99]. In addition, the longer the time period, the higher the likelihood of organic or microbiological deposition on microplates due to surface roughness [100] and/or ionic group changes [97]. Biofilms made up of organic components, microorganisms, and algae are rich in microplastics that have disintegrated over time. When this occurs, the substance may readily enter the food chain, since the microorganisms and algae in the biofilm serve as food for certain groups of species [101]. Copepods typically consume microplastics that have been in the environment longer, because these older plastics develop a biofilm of natural microbes, which contains similar prey and emits chemicals that make the particles more enticing as food [101]. Additionally, recent research has delved into the potential of plastics to serve as a carbon source for microorganisms, which can further boost biofilm development [102]. Consequently, microplastics create localized micro-hotspots characterized by heightened microbial activity, thereby instigating alterations in carbon cycling dynamics. Therefore, the longer that microplastics remain in the environment, the greater the likelihood that they will enter the food chain. Vertical transport, which refers to the movement of microplastics from the surface (floating) to the bottom of the sea or ocean, is a growing area of study in the field of microplastics. Research has identified several variables that contribute to this phenomenon.