# The Microplastics Cycle: An In-Depth Look at a Complex Topic
## 2 The Microplastics Cycle
### Microplastics in Freshwater
Several articles have identified that microplastics can serve as a substrate for biofilm formation [73]. When microplastics age, their surfaces roughen, creating increased crevices that can create a favorable habitat for biofilm development and other pollutants and pathogens to adhere [74; 75]. Biofilms formed on microplastics can have a significant impact in the adhesion and concentration of pollutants [76]. Polyvinyl chloride plastics (PVC) with biofilms absorb approximately 50 percent more of the antibiotic norfloxacin than PVC without biofilms. Similarly, high density polyethylene (HDPE) and polyamide (PA) microplastics with biofilm absorbed 46 percent and 24 percent more norfloxacin, respectively, than HDPE and PE microplastics without biofilm [77]. Metal adsorption on microplastics depends heavily on intraparticle diffusion. In addition, a rise in temperature and a decrease in salinity boost the affinity of metals and microplastics [78]. Different kinds of microplastics and metals exhibit varying degrees of adherence. PE microplastics have a stronger affinity for metals than PS microplastics, whereas PP microplastics have an even greater attraction [79]. Furthermore, the adsorption of microplastics on metals varies, depending on the microplastics' particle size [79]. The surface carbonyl group of PS microplastics interacts with the biogeochemistry of silver to produce silver nanoparticles [80]. Additionally, viruses may also adhere to the surface of microplastics. However, the adsorption affinity of microplastics varies on their size and surface functional group [81]. The complexities of the degradation of plastics into microplastics, driven by microbes and biofilms, raises questions about the impact of these plastics on the microbes themselves and their integral role in the ecosystem. It also raises questions about the impact of these plastics, and their integral role in the ecosystem on the very microbes themselves and the wider ecological balance. In addition to interactions of microplastics and biofilms, several papers have identified interactions between microalgae and microplastics. Microalgae are at the base of the food chain, and subtle impacts to them may affect the whole food chain. Microplastics can inhibit the development of the microalgae _Chlorella pyrenoidosis_, modify oxidative stress, and compromise cell membrane integrity [82]. Microplastics can also inhibit the photosynthetic activity of _Chlorella vulgaris_. Microplastics also dramatically decreased peroxidase and glutathione reductase levels in _C. vulgaris_, while increasing superoxide dismutase levels [83]. Additionally, when organic pollutants such as amoxicillin, ibuprofen, serntraline, and simazine are adsorbed onto microplastics, the combined disruption of this combination has a substantial impact on the photosynthetic activity of _Scenedesmus armatus_[84]. Further concern is raised when examining the interactions specifically with cyanobacteria and microplastics. [PERSON] and [PERSON] [85] found that microplastics exerted a dual effect on _Anabena variabilis_ growth, stimulating it at lower concentrations but inhibiting it at higher levels (>0.3 mg/mL) across a temperature range of 2.5-32.5 \({}^{\circ}\)C. As the concentration of microplastics increased, shading by the microplastics may have induced stress, which corresponded with an observed increase in extracellular polymeric substance (EPS) production by _A. variabilis_, which enhanced microplastic deposition. This complex interplay suggests that microplastics may play a role in cyanobacterial blooms, potentially impacting their deposition dynamics. In eutrophic reservoirs, microplastics can serve as vectors for potentially harmful cyanobacterial toxins, specifically microcyst-LR and microcstin-LF [86]. The interaction between cyanobacteria and calcium plays a crucial role in facilitating the sedimentation of microplastics within these ecosystems [87].