## 3 Results and Discussion
### pH Effect on Sorption Affinity of Organic Pollutants on MPs  
In this study, the adsorption behaviors of the three selected groups of organic pollutants on MPs were obtained at three different pH values (pH 4, 7 and 10) in order to cover the widest possible range of pH values in a water environment. Figures S4-S6 show that changes in the pH value of the water matrix had the highest impact in the case of the selected CPs. On the other hand, changes in pH value had a very low impact on the adsorption behavior of the selected PAHs and HBs on MPs. The obtained results shown in Figure S6 imply that the highest percentage of adsorption of CPs was observed at pH 7 (25 to 68%). The adsorbed percentage of 4-CP adsorbed on MPs was in the following order: PP (30%)! PE_PCPs_1 \(\approx\) PE_PCPs_2 \(\approx\) PLA (35-40%)! Pep \(\approx\) PEg (48%)! PET (60%). Furthermore, the results imply an increase in the adsorption percentage of 2,4-DCP onto MPs as follows: PE_PCPs_1 (40%)! PE_PCPs_2 \(\approx\) PEg \(\approx\) PLA (50%)! Pep \(\approx\) PET \(\approx\) PP (65%). The adsorption affinity of 2,4,6-TCP and PCP on MPs was the highest with PP, PLA, PE_PCPs_2 and PEg (around 50-60%). A slightly lower adsorption percentage was determined for 2,4,6-TCP and PCP on PEp and PE_PCPs_1 (30-40%), while the lowest was found with PET, at 25-30%. Based on the physico-chemical characteristics of the CPs shown in Table S2, or to be precise, the pK\({}_{\text{a}}\) values of the acid constants, it can be seen that at pH 4, the selected CPs used in this study were in their molecular form, while at pH 10, they were in their ionic form. Additionally, based on the experimentally determined pH_PZC_ of the MPs at pH 4, all selected microplastic particles (PEp, PE_PCPs_1, PE_PCPs_2, PEg, PET, PP and PLA) were positively charged, while at pH 10, their surfaces were negatively charged. Therefore, at pH 4 in water, the binding percentage was low due to the impossibility of interaction between the positively charged surfaces of the MPs and CPs in their molecular form [50,51]. On the other hand, at pH 10, the surface of the MPs was negatively charged, and the investigated CPs were in an ionic, negatively charged form. Considering this fact, at pH 10, the selected CPs were repelled from the surface of the MPs and a low percentage of interactions occurred in comparison to pH 7 [50,51]. Based on the obtained results, a slight influence of the pH value on the formation of interactions between the tested benzene derivatives and MPs was observed. It was also possible to observe a significantly higher binding percentage compared to the results obtained for CPs (Figures S4 and S5). This behavior can be explained by the higher hydrophobicity of the selected benzene derivatives compared to CPs, which led to their higher affinity towards adsorption on MPs [52,53]. Based on the results shown in Figure S5, the selected HBs had the highest adsorption affinity toward the PE standard and those isolated from cosmetic preparations (PE_PCPs_1 and PE_PCPs_2). Additionally, there was an increase in the percentage of HBs that increased in hydrophobicity in the range of 55-99%. Thus, the binding percentage of HBs changed in the following order: 1,2,3-TeCB! 1,3,5-TeCB! 1,2,4-TeCB! PeCB! HeCB! TFL. The results shown in Figure S5 imply that the selected HBs had a significantly lower affinity for PLA (30-90%) in comparison to the selected nondegradable MPs. Similar results were obtained in terms of the influence of the pH value on the adsorption of PAH on the MPs. Based on the results shown in Figure S6, an insignificant influence of the pH value on the formation of interactions between the selected PAHs and MPs can be observed.