## 1 Introduction
Several studies have emphasized the impact of pH as an environmental factor in increasing or inhibiting the adsorption capacity depending on the polymer type as well as the type of pollution [19; 20]. In this regard, previous research results have implied that the surfaces of polyethylene and polystyrene particles change and protonate with decreases in pH, consequently increasing the sorption of organic pollutants, such as perfluorooctane sulfonate, chlorinated phenols and others [3; 21; 22; 23]. Moreover, variable pHs in the surrounding water may change the ionization states of pollutants and influence their sorption processes on MPs [3; 21; 22; 23]. Among the various  
Figure 1: Most important factors influencing the sorption of pollutants on MPs. studies investigating the adsorption of various organic pollutants (such as pesticides or pharmaceuticals) on a number of MPs [23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35], pH was not always considered. However, as one of the main factors, the influence of pH on the sorption behavior of MPs is not yet fully understood and should be investigated further. Specifically, the amount of information available about how pH affects the adsorption mechanism of organic pollutants is limited. The majority of the research on aquatic pollution caused by MPs has been focused on marine environments, as well as on the interaction between MPs and both organic and inorganic pollutants. Inland waters play a major role in transporting MPs from generation sites, such as non-point pollution sources and wastewaters, to the ocean, as well as to coastal areas and inland seas. Furthermore, the higher concentrations of microplastic particles and pollutants in inland waters could result in a significant difference in the interactions between MPs and pollutants in these water bodies [36]. Additionally, there is a wide range of studies highlighting concerns about the sorption interactions between MPs and single-solute systems, often neglecting the fact that mixtures of pollutants are more common in natural environments. The behavior of organic pollutants in mixtures can be very different compared to single-compound systems, and highly complex sorption interactions can occur with adsorbents such as MPs. Thus, only studying the sorption process in single-solute systems may not be enough to predict the interaction between organic pollutants and MPs in water environments [19; 37; 38; 39]. Based on previous discussion and our earlier studies, we hypothesized that various MPs have different sorption capacities for specific groups of organic pollutants, and due to their different physico-chemical characteristics, the sorption behaviors of mixture solutions of selected groups of organic pollutants chlorinated phenols (CPs), polycyclic aromatic hydrocarbons (PAHs) and halogenated benzenes (HBs) on MPs can be influenced by environmental factors. Therefore, the main objective of this study was to investigate the influence of one of the most important environmental factors, pH value, on the adsorption behaviors and mechanisms of mixture solutions of selected groups of organic pollutants, CPs, PAHs and HBs, on seven types of MPs that are frequently detected in water environments.