## 3 Result Statements from the Analysis of the Available Literature
### Microplastics: Delivery Vehicles for Micropolultants in Aquatic Environments
#### 3.1.1 Factors Influencing the Sorption Capacity of Microplastics to Micro-Pollutants  
There is an increased risk of the release and transfer of additives from plastics to the surrounding environment or organisms during the degradation processes or particle ageing [61]. Due to mechanical, chemical, biological, and/or UV ageing processes, the microplastic particles' physicochemical and mechanical properties, texture, and appearance change over time [62]. These changes were noted as the main causes of the altered sorption capacity of microplastics to micro-pollutants [63; 64; 65]. Microplastic sorption capacity depends on the interaction between microplastics and micro-pollutants in an environment that increases or decreases their affinities to each other and influences the number of adsorbed micro-pollutants (Figure 1).  
The physicochemical properties and age of microplastics interrelate in a variety of complex ways that affect sorption capacity. Color, density, specific surface area, and free volume are some of the physical properties of microplastics with the potential to affect their sorption capacity [66]. For instance, lighter-colored microplastics could adsorb lower-molecular-weight polycyclic aromatic hydrocarbons (PAHs) as well as interact with lower concentrations of PAHs and polychlorinated biphenyls (PCBs) when compared to darker-colored microplastics [67; 68]. Particle density also plays a role in sorption behavior, as microplastics with a higher density are capable of adsorbing lower concentrations of PAHs, PCBs, and phenanthrene compared to lower-density microplastic particles [69; 70; 71]. For example, polyethylene, with its characteristically large specific surface area and free volume, allowed more micro-pollutants to diffuse into the looser network of its polymer structure, suggesting a reason for its higher sorption capacity compared to the other microplastic types [70; 72; 73].  
Chemical Properties of Microplastics and Micro-Pollutants  
Micoplastic chemical properties, such as composition, crystallinity, planarity, surface charge, functional group, and chemical interaction potential, could also be considered as factors that have an influence on sorption capacity [74; 75; 76; 77]. A decrease in crystallinity found in rubbery plastics with amorphous regions, such as polyethylene, results in increased hydrophobic organic compounds (HOCs) sorption compared to glassy plastics, such as polystyrene [78; 79; 80]. Further, the chemical properties of micro-pollutants could also play a significant role in their interactions with microplastics, thereby affecting the sorption capacity. The varying microplastic sorption capacity for micro-pollutants, hydrophobic and hydrophilic compounds, and heavy metals is strongly dependent on type of reaction, including hydrophobicity, partitioning, Van der Waals forces, electrostatic interaction, \(\pi\)-\(\pi\) interaction, and hydrogen bonding interaction [81].  
Microplastic age can be a pivotal attribute of sorption capacity alteration. Ageing represents the accumulation of changes in microplastics over time, including changes in physicochemical properties [81]. The increased frequency or induction of oxygen-containing functional groups (e.g., hydroxyl, carbonyl, and formyl groups) occurs after the particles' exposure to ageing [82; 83; 84]. It has been reported that oxygen-containing functional groups, emerging during the microplastic ageing process, could interact with hydrophilic micro-pollutants by forming hydrogen bonds and increase the affinity between these chemicals [81; 82; 85]. The relatively high concentration of heavy metals found on aged polyethylene compared with the pristine polyethylene terephthalate (PET) can be  
Figure 1: Major factors and sub-factors influencing the sorption capacity of microplastics to micro-pollutants.  
related to the higher partition coefficient, resulting from the different chemical properties and biofilms [86,87].