## 3 Results and Discussion
### The pH Effect on Adsorption Kinetics of CPs on MPs  
The results of the sorption kinetics of CPs on the PEp, PE_PCPs_1, PE_PCPs_2, PEg, PET, PP and PLA particles at different pH levels in the water matrix are shown in Figure 2. After 12-48 h, the adsorption of the selected CPs onto the MPs reached equilibrium, depending on the sorbate-sorbent combinations investigated. As shown in Figure 2, the uptake of CPs by the selected MPs and PLA increased with time, until the sorption equilibrium was achieved after 12 h in the case of powdered MPs and 48 h for granulated MPs. These results are in the range of the usually reported periods for the sorption equilibria of organic compounds on various types of MPs. The powdered MPs had the highest uptake for all selected CPs at neutral pH, or pH 7, and the highest adsorption affinity at pH 7 was obtained for 2,4-DCP (221.0 \(\mu\)g/g). The other three selected CPs indicated lower adsorption affinities compared to 2,4-DCP (137.7 \(\mu\)g/g, 162.0 \(\mu\)g/g and 90.74 \(\mu\)g/g for 4-CP, 2,4,6-TCP and PCP, respectively). The lower adsorption affinities toward these types of MPs could be a consequence of both the physico-chemical properties of the compounds and their molecular structures. Based on the physico-chemical properties of the selected CPs, as shown in Table S2, it could be assumed that PCP would exhibit the greatest change in its percentage of adsorption on PEp due to its low solubility in water and its high hydrophobicity compared to the other tested CPs. The influence of the hydrophobicity of molecules on the adsorption of organic compounds on MPs was pointed out by [PERSON] and [PERSON] (2018), who concluded that compounds with higher hydrophobicity are better adsorbed on MPs. However, the amount of PCP adsorbed was the smallest, which could be a consequence of the size of the molecule and the position of chlorine atoms in the PCP molecule, which may hinder the approach of the hydroxyl group to the surface of PEp, and thus hinder its adsorption. Furthermore, this confirms the chemical structure of 2,4-DCP and 2,4,6-TCP, where with the decrease in the number of chlorine atoms, the adsorption affinity increased (qt = 221 \(\mu\)g/g for 2,4-DCP and qt = 162.0 \(\mu\)g/g for 2,4,6-TCP) [22; 54]. In order to investigate the adsorption behavior of the CPs in the presence of other types of MPs in water, PET and PP were selected since they are often detected in the environment [55; 56]. The highest adsorption affinity at pH 7 towards PET was obtained by 2,4-DCP (qt = 125 \(\mu\)g/g). The adsorption affinity of CPs to PET further decreased in the following order: 2,4,6-TCP \(\approx\) 4-CP \(>\) PCP; the adsorbed amounts for 2,4,6-TCP and 4-CP were 67 \(\mu\)g/g and 25 \(\mu\)g/g for PCP. The obtained results for the adsorption kinetic of the CPs on PLA implied that the highest adsorption affinity has 2,4,6-TCP and PCP, where the qt after 24 h was 110 \(\mu\)g/g and 100 \(\mu\)g/g, respectively. The lowest adsorption affinity of CPs on PLA was obtained for 4-CP, qt = 85 \(\mu\)g/g. Figure 2: Experimental adsorption of (**a**) 4-CP; (**b**) 2,4-DCP; (**c**) 2,4,6-TCP and (**d**) PCP on PEp, PE_PCPs_1, PE_PCPs_2, PEg, PET, PP and PLA in water at different pH values (n = 2). On the other hand, the obtained results shown in Figure 2 indicate that at pH 4, the adsorption affinity of all selected CPs towards MPs decreased in comparison with the data obtained at pH 7. They also imply that, regardless of the pH, the highest adsorption affinity of CPs was obtained with the powdered MPs. Additionally, at pH 4, the highest adsorbed amount was obtained for 2,4-DCP on PE isolated from personal care products (73.8-91.0 \(\upmu\)g/g). As in the case of pH 7, at a lower pH in the water matrix (pH 4), the adsorbed amount decreased for CPs with higher hydrophobicity but larger molecule structure. Therefore, the adsorbed amount of 2,4,6-TCP and PCP on PE isolated from personal care products ranged between 47.7 and 66.9 \(\upmu\)g/g and 55.9 and 58.8 \(\upmu\)g/g, respectively.