Pharmaceuticals, Pesticides, and Poly- and Perfluoroalkyl Substances at Surface Water Occurrence Levels—Impact of Compound Specific Physicochemical Properties on Nanofiltration and Reverse Osmosis Processes

Received: 3 November 2025 Revised: 23 November 2025 Accepted: 25 November 2025 Published: 27 November 2025 Citation: Šurlan, J.; Galinha, C.F.; Maravi´c, N.; Brazinha, C.; Anti´c, I.; Živanˇcev, J.; Ðuriši´c-Mladenovi´c, N.; Šereš, Z.; Crespo, J.G. Pharmaceuticals, Pesticides, and Polyand Perfluoroalkyl Substances at Surface Water Occurrence Levels—Impact of Compound Specific Physicochemical Properties on Nanofiltration and Reverse Osmosis Processes. Membranes 2025, 15, 358. https://doi.org/10.3390/ membranes15120358 Copyright: © 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/ licenses/by/4.0/). Article Pharmaceuticals, Pesticides, and Polyand Perfluoroalkyl Substances at Surface Water Occurrence Levels—Impact of Compound Specific Physicochemical Properties on Nanofiltration and Reverse Osmosis Processes Jelena Šurlan 1, Claudia F. Galinha 2, Nikola Maravi´c 1,* , Carla Brazinha 3,4 , Igor Anti´c 1, Jelena Živanˇcev 1, Nataša Ðuriši´c-Mladenovi´c 1, Zita Šereš 1and João G. Crespo 2,5 1Faculty of Technology Novi Sad, University of Novi Sad, Bul. Cara Lazara 1, 21000 Novi Sad, Serbia 2LAQV-REQUIMTE, Department of Chemistry, NOVA School of Science and Technology, FCT NOVA, Unversidade NOVA de Lisboa, 2829-516 Caparica, Portugal 3Department of Bioengineering and iBB—Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal 4Associate Laboratory i4HB—Institute for Health and Bioeconomy, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal 5 Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal *Correspondence: [email protected]; Tel.: +381-21-485-3685 Abstract Pharmaceutically active compounds (PhACs), pesticides, and polyand perfluoroalkyl substances (PFAS) are increasingly detected in surface waters at trace concentrations, raising concerns for both aquatic systems and, consequently, human health. Conventional solutions are insufficient to achieve complete removal at trace compound concentrations, highlighting the need for advanced separation technologies. This study aims to comprehensively analyze rejection and removal mechanisms of selected PhACs, pesticides, and PFAS present in water solutions at reported environmentally relevant concentrations (300 ng L −1 ), using two nanofiltration (NF) and one reverse osmosis (RO) polyamide membrane. PhACs, pesticides, and PFAS were selected to cover a broad range of physicochemical properties, specifically molecular mass (MM), dissociation constant (pKa), and octanol–water partition coefficient (logK o/w ). Rejection values ranged from 42.1% (acetaminophen) to apparent 100% (for multiple compounds), depending on water pH, solute properties, and membrane characteristics. Size exclusion and electrostatic interactions were identified as the primary removal mechanisms, with hydrophobic interactions having a lower impact, particularly for carbamazepine, bezafibrate, and perfluorooctane sulfonic acid (PFOS). Addition of sodium chloride (3 g L −1 ) decreased rejection of most negatively charged compounds due to suppression of membrane surface charge, although clarithromycin and ofloxacin exhibited improved rejection. Presented results provide fundamental insight into compound-specific membrane rejection and highlight the importance of membrane–solute interactions under environmentally realistic conditions. The results support further optimization of NF and RO for targeted compound rejection and provide a baseline for data-driven membrane process modeling. Keywords: water treatment; pharmaceuticals; pesticides; PFAS; nanofiltration; reverse osmosis Membranes 2025,15, 358 https://doi.org/10.3390/membranes15120358 Membranes 2025,15, 358 2 of 20 1. Introduction Contaminants of emerging concern (CECs), such as PhACs, pesticides, and PFAS, are ubiquitously present in the environment with many of them extremely persistent, presenting a major challenge to human health and aquatic fauna [ 1 – 3 ]. Conventional wastewater treatment processes, including flocculation, sedimentation, microand ultrafiltration, and disinfection, are inefficient for complete CECs removal, and thus wastewater discharge is among the primary sources of numerous CECs in aquatic systems. On the other hand, advanced technologies, such as NF and RO, are often considered for achieving efficient removal of micropollutants [ 4 – 7 ]. Compared to RO membranes that, due to the small pore size ( ≈ 0.25 nm), reject most ions ( ≈ 0.25 nm), NF membranes have higher pore size (0.5–2 nm) , permeability, and selectivity towards divalent and polyvalent ions, while allowing passage of monovalent ions and small molecules [ 8 ]. Both NF and RO membranes are widely studied in water treatment processes due to the ability to remove different pollutants with low molecular mass (MM), including some CECs [ 9 , 10 ]. CECs removal using NF and RO is dependent on multiple factors, including operating parameters, solution properties, membrane characteristics, and CECs physicochemical properties [9,11–14]. Multiple studies have reported on removal of PhACs, pesticides, and PFAS from various water samples [ 10 , 11 , 13 – 24 ]; however, most of the reviewed studies focused on the influence of operating parameters, solution properties, and membrane characteristics on CECs removal. Detailed research focusing on specific correlations between individual CECs’ physicochemical properties and membrane rejection is still scarce. In particular, it remains unclear which molecular descriptor most reliably predicts and affects solute–membrane interactions across different membrane types and operating conditions [25]. Understanding the correlation between main CECs properties (MM, pKa, and logK o/w ) and membrane rejection at different operating conditions can provide valuable information regarding membrane process optimization for specific CECs removal. Furthermore, most of the reviewed studies focus on higher concentrations of CECs compared to occurrence concentrations reported in surface waters (pg/Lµ g/L) [ 3 ]. Therefore, there is a critical need for studies that not only investigate how CECs’ specific molecular descriptors govern membrane rejection but also evaluate CECs removal at environmentally relevant concentrations. The aim of this study is to evaluate the potential of selected NF and RO membranes for the removal of target PhACs, pesticides, and PFAS representatives having different physicochemical properties at environmentally relevant concentrations in water samples and provide a detailed insight into the relation between individual CECs’ molecular descriptors and membrane rejection at different operating conditions. This study employed ultrapure water spiked with selected CECs at matching environmental occurrence levels as a model matrix to allow controlled, reproducible conditions and to isolate the effects of target compounds on NF/RO rejection performance without the variability introduced by natural organic matter, colloids, or other co-contaminants. This work was performed at concentrations representative of real-world occurrence levels [ 26 – 28 ]. The primary aim was to investigate fundamental removal mechanisms under well-defined conditions before introducing additional complexity. Future work will extend these investigations to environmentally relevant matrices, incorporating natural organic matter and particulate matter to evaluate fouling behavior, long-term performance, and scalability under realistic conditions. Discussion concerning permeate fluxes obtained during the process was excluded in order to focus on identifying relevant solute removal mechanisms. Furthermore, impact of sodium chloride presence in water samples was evaluated in experiments where RO membrane was used, since high levels of salts are often present in various water bodies, due to saltwater intrusion, climate change impact (droughts), evaporation in closed Membranes 2025,15, 358 3 of 20 basins, industrial discharges with high salt concentration, etc. The findings of this study contribute to a better understanding of the key factors influencing PhACs, pesticides, and PFAS removal by membrane-based processes, providing valuable insights for optimizing treatment processes and improving water quality management. 2. Materials and Methods 2.1. Chemicals and Reagents Fourteen compounds were initially selected for investigation; however, the final results on the efficiency of membrane processes are presented for twelve compounds due to limitations of the applied analytical method, as explained later. Six PhACs, four pesticides, and four PFAS were initially selected as CECs representatives based on their differences in physicochemical properties, more specifically MM, pKa, and logK o/w (Table 1). MM of selected CECs ranges from 151.2 Da to 748.0 Da. Nine selected CECs are considered hydrophobic (logK o/w > 2) and five CECs are classified as hydrophilic (log K o/w < 2), based on the logK o/w value limit [ 29 ]. Based on their pKa value, four CECs are positively charged, two are neutral, and eight are negatively charged at pH 7. Table 1. Structure and properties of selected PhACs, pesticides, and PFAS. CECs Structure MM (Da) apKa alogKo/w aHydrophobicity b Pharmaceutically active compounds Clarithromycin 748.0 8.99 3.16 Hydrophobic Ofloxacin 361.4 5.97–8.22 –0.39 Hydrophilic Carbamazepine 236.3 2.3 2.45 Hydrophobic Acetaminophen 151.2 9.38/9.7 0.46 Hydrophilic Salbutamol 239.3 9.1–10.4 1.4 –0.64 Hydrophilic Bezafibrate 361.8 3.6 4.3 Hydrophobic Pesticides Carbofuran 221.3 11.9 2.32 Hydrophobic Acetamiprid 222.7 0.7 0.8 Hydrophilic Membranes 2025,15, 358 4 of 20 Table 1. Cont. CECs Structure MM (Da) apKa alogKo/w aHydrophobicity b Pesticides Malathion 330.4 6.8 2.36 Hydrophobic Propiconazole 342.2 1.09 3.7 Hydrophobic PFAS Perfluorooctane sulfonamide (PFOSA) 499.1 6.2 5.8 Hydrophobic Perfluorooctane sulfonic acid (PFOS) 500.1 0.14 4.49 Hydrophobic Perfluorobutanoic acid (PFBA) 214.0 0.08 2.2 Hydrophobic Perfluorobutane sulfonic acid (PFBS) 300.1 –3.31 1.82 Hydrophilic a Pubchem, Chemspider; b determined based on logK o/w value (logK o/w > 2 hydrophobic, logK o/w < 2 hydrophilic) [29]. Samples were prepared using high-purity CECs standards from Sigma Aldrich (St. Louis, MO, USA) or LGC (Augsburg, Germany). Purities of the used analytical standards were as follows: clarithromycin (99%), ofloxacin (>95%), carbamazepine (100%), acetaminophen (>99%), salbutamol (100%), bezafibrate (99%), carbofuran (>99%), acetamiprid (>99%), malathion (>99%), propiconazole (>98%), PFOSA (>97%), PFOS (100%), PFBA (100%), and PFBS (>99%). Stock solution with targeted PhACs, pesticides, and PFAS was prepared using LC-MS grade methanol (MeOH, ≥ 99.9%) (VWR International, Radnor, PA, USA). Ultrapure (Milli Q) water (18 M Ω cm) (Advantage system from Millipore, Molsheim, France), was used for model water (feed) preparation. Diluted sodium hydroxide (>98%) and hydrochloric acid (>36.5%) solutions (concentration 0.1 mol L −1 ) were used to set solution pH value at pH 4, pH 7, and pH 10. Sodium chloride (>99.5%) was added in RO feed solution at pH 7 in a concentration relevant in brackish water treatment (3 g L−1). 2.2. NF and RO Experiments Feed solutions were prepared in Milli Q water by spiking the water with solution containing PhACs, pesticides, and PFAS (concentration of each individual CEC in each feed solution was 300 ng L −1 ), followed by pH adjustment and sodium chloride addition. The target concentration of 300 ng L −1 for each compound in the spiked model mixture was selected based on concentrations previously reported for CECs in surface water and treated wastewater effluents. Numerous monitoring studies have documented CECs occurrence in the low ng/L to low µ g/L range, with median or mean concentrations for many pharmaceuticals and personal care products frequently falling between 100 and 500 ng/L [26–30]. Three thin-film composite (TFC) polyamide membranes (SW30HR, Desal-5 DK, and NF270) were selected based on the differences in molecular weight cut off (MWCO), according to the manufacturers’ specifications. Relevant characteristics of the selected membranes are shown in Table 2. Membranes 2025,15, 358 5 of 20 Table 2. Characteristics of the selected NF and RO membranes. Commercial Name SW30HR Desal-5 DK NF270 Type RO NF NF Manufacturer FilmTec™ SUEZ FilmTec™ Material aTFC polyamide TFC polyamide TFC polyamide MWCO (Da) a100 150–300 400 pH range a2–11 2–10 2–11 pKa 4.0 d4.1 c3.3/5.0 b Surface charge at pH 4 eneutral neutral neutral Surface charge at pH 7 enegative negative negative Surface charge at pH 10 enegative negative negative a According to the manufacturers’ specifications; b [ 31 , 32 ]; c [ 33 ]; d [ 32 ]; e determined based on pKa value (pH = pKa, neutral; pH > pKa, negative). Experiments were conducted in a METCell dead-end stirred cell unit from Evonik Industries AG (Essen, Germany) (Figure S1 in Supplementary Material ). The active surface area of the membrane is 51.4 cm 2 . Prior to conducting the experiments, membranes were soaked in ultrapure water for 24 h. High pressure nitrogen gas cylinder with a pressure regulator was used to adjust the pressure in the feed compartment. Prior to the addition of feed solution, membranes were compacted in the cell unit with ultrapure water until a constant flux was obtained. Pressure for each membrane was chosen based on the flow of the ultrapure water through the pristine membrane, in order to achieve similar duration of each experiment. Pressure was set based on the membrane permeate flow at 3 bar, 10 bar, and 30 bar for NF270, Desal-5 DK, and SW30HR membranes, respectively, and was kept constant throughout the experiments. Feed solutions were stirred at 450 rpm for the duration of the experiments. This vigorous stirring ensured that no external mass transfer limitations occur (experimentally validated). Membrane flux was monitored for the duration of the experiments by acquisition of the permeate mass with an accuracy of 0.01 g. Permeate flow, Q p (L h −1 ), and permeate flux, J(L h −1 cm −2 ), were calculated using the following equations, respectively: Qp=V t(1) J=Qp A(2) where V(L) and t(h) represent permeate volume and time of permeate collection, respectively, whereas Arepresents the membrane surface area (cm2). The experiments lasted until the first 100 mL of permeate were collected, with a remaining 100 mL of retentate. Concentrations of targeted PhACs, pesticides, and PFAS were analyzed in the feed, permeate, and retentate solutions. Apparent rejections, R(%), were calculated using the following equation: R=cr cr+cp∗100 (3) where c r and c p represent CECs concentration (ng mL −1 ) in retentate (concentration in the feed compartment in each instant) and permeate, respectively. Results and discussion of membrane adsorption were not included in the corresponding article, since adsorbed CECs amounts to the membrane surface are below the limit of quantification for UHPLCMS/MS, due to low, but environmentally relevant, initial CECs concentration. Therefore, Equation (3) was used in order to more clearly evaluate rejection and removal mechanisms Membranes 2025,15, 358 6 of 20 without the interference of possible adsorption onto membrane surface. Specific values of measured data are provided in metadata file. Rejection values presented in Section 3 are shown without errors and standard deviation values; however, charts with errors are shown in Figure S1 in Supplementary Material. In experiments where c p was below the limit of detection, c p was considered as a non-detectable concentration, and the calculated R value was assumed to be 100%. 2.3. Sample Preparation and Instrumental Analysis Sample preparation was carried out using the previously described method in a study published by Petrovi´c et al. (2014) [ 34 ]. Briefly, preparation of collected sample solutions (feed, permeate, and retentate) for instrumental analysis included solid phase extraction (SPE). SPE was performed by using single-layer sorbents (Oasis HLB, 200 mg, 6 mL, Waters Corporation, Milford, MA, USA). HLB sorbents were selected based on their hydrophilic–lipophilic nature, which enables extraction of a wide range of CECs with different physicochemical properties. Cartridges were positioned in a vacuum manifold and conditioned by 5 mL of MeOH and 5 mL of ultrapure water, followed by loading the sample and rinsing with 5 mL of ultrapure water. Afterwards, sorbents were dried for 2 h by passing air through the sorbent. Targeted CECs were eluted from the sorbents with MeOH (2 × 4 mL). Obtained eluates were evaporated to dryness at 30 ◦ C under a nitrogen stream and reconstituted in 1 mL of first gradient mobile phase. High-performance liquid chromatography coupled with triple quadrupole mass spectrometry, UHPLC-MS/MS (Thermo Fisher Scientific, Waltham, MA, USA), was used for instrumental analysis of selected CECs, which is described in detail in a study published by Raki´c et al. (2023) [ 35 ]. Conditions and methodology for instrumental analysis are described in detail in Supplementary Material. Recoveries determined for all 14 initially selected compounds are presented in Supplementary Material (Table S3). Although four PFAS were included in model feed solutions, rejection values for two of them, perfluorooctane sulfonamide (PFOSA) and perfluorobutanoic acid (PFBA), were not considered in this study due to the very low recoveries. Specifically, mean recoveries were 7.36% for PFOSA and 20.92% for PFBA (Table S3 in Supplementary Material), which are considered insufficient for reliable quantification and, consequently, for robust calculation of rejection. Hydrophilic–lipophilic balance (HLB) polymeric sorbents, due to their “dual nature”, can be applied for PFAS extraction; however, low recoveries could be expected for short-chain perfluoroalkyl carboxylic acids [ 36 ], e.g., PFBA, due to inefficient retention onto the sorbent [ 37 ]. This behavior is in agreement with previous reports showing poor HLB retention and low recoveries for short-chain PFCAs, including PFBA [ 38 , 39 ]. Additionally, PFOSA exhibits pH-dependent extraction behavior, with optimal recoveries at pH 8 [ 40 ], whereas in this work, pH 7 was selected as a compromise condition to enable simultaneous extraction of CECs with diverse physicochemical properties. For these reasons, PFOSA and PFBA were excluded from the rejection evaluation. Additionally, lower recovery was observed for ofloxacin (~46%), probably due to its high hydrophilicity, which may hinder efficient extraction by HLB polymeric cartridges. Nevertheless, the results on rejection values for this compound are presented here, as it is assumed that the same recovery rate applies to this compound in both c r and c p samples. Consequently, the percentage ratio calculated using Equation (3) remains unaffected, providing valuable insights into ofloxacin removal. According to Gros et al. (2012) [ 41 ], it is challenging to find optimal conditions for each target analyte in multi-residue methodologies; therefore, it is necessary to select optimal conditions for the highest number of compounds. Recoveries of all selected CECs are given in the Supplementary Material. Membranes 2025,15, 358 7 of 20 3. Results and Discussion Three polyamide membranes with different MWCO (SW30HR, Desal-5 DK, and NF270) were selected for thorough analysis of CECs rejections at different operating pH values. Twelve CECs, including six PhACs, four pesticides, and two PFAS, were selected in order to cover a wide range of molecular descriptors (MM, pKa, and logK o/w ) and evaluate the impact of each descriptor on solute rejection and associated mechanisms. Tables 1and 2 summarize CECs’ physicochemical properties and selected membranes’ properties, respectively. 3.1. Impact of CECs’ Physicochemical Properties and Operating pH on CECs Rejection Rejection values of twelve targeted CECs (including two PFAS, four pesticides, and six PhACs) at three pH values by using SW30HR, Desal-5 DK, and NF270 membranes are shown in Figures 1–3, respectively. Figure 1. PhACs, pesticides, and PFAS rejection values (sorted by increasing MM) at pH 4, pH 7, and pH 10 by using the SW30HR membrane. Membranes 2025,15, 358 8 of 20 Figure 2. PhACs, pesticides, and PFAS rejection values (sorted by increasing MM) at pH 4, pH 7, and pH 10 by using the Desal-5 DK membrane. Figure 3. PhACs, pesticides, and PFAS rejection values (sorted by increasing MM) at pH 4, pH 7, and pH 10 by using the NF270 membrane. Membranes 2025,15, 358 9 of 20 Rejection values ranged from 42.1% to apparent 100% by selected membranes. Rejection values of the same compound varied greatly depending on selected membrane and operating pH. Figures 1–3allow, by a simple visual observation, a confirmation of the relevance of size exclusion on the rejection of the selected solutes. It seems clear that there is a general trend confirming that the tighter the membrane, the higher the solute rejection (sequence SW30HR, Desal-5 DK, and NF270) as previously reported in numerous studies [ 42 , 43 ]. However, at pH 4, the observed rejection pattern did not fully conform to this expected trend. Also, from these figures it can easily be concluded that, in general, at higher pH, where the membranes under study are negatively charged, as well as the selected solutes, rejection is higher due to charge repulsion, confirming the relevance of electrostatic mechanisms in solute rejection. It should also be noticed that when using the SW30HR membrane, the lowest rejection values regarding all tested PhACs, pesticides, and PFAS were obtained at pH 4. Even though differences in CECs’ molecular descriptors were significant in terms of MM, pKa, and logK o/w , rejection values remained low for all samples at pH 4. Therefore, it can be assumed that lower rejection values obtained were caused by changes in the SW30HR membrane. Polyamide membranes are extremely sensitive to external factors (such as operating pH), which could influence the membrane swelling, therefore increasing the space between the membrane fibers and increasing permeation of CECs through the membrane. However, further research focused on SW30HR properties is required to determine the exact cause for lower performance of SW30HR membrane at pH 4. In the following sections, rejection values and removal mechanisms of each individual PhAC, pesticide, and PFAS, with the three selected membranes and three operating pH values, are thoroughly discussed, focusing on CECs’ specific properties presented in Table 1 (MM, pKa, and logKo/w). 3.1.1. Acetaminophen Rejection values of acetaminophen at pH 4 decreased with an increase in MWCO of the membrane (SW30HR > Desal-5 DK > NF270). Relatively low rejection values of acetaminophen (MM = 151.2 Da) by Desal-5 DK and NF270 membranes (MWCO 150–300 Da and 400 Da, respectively), in addition to uncharged membrane surfaces at pH 4 (Table 2), suggest size exclusion as the main removal mechanism at pH 4. Increase in operating pH to pH 7 decreased acetaminophen rejection value when using the Desal-5 DK membrane, whereas the rejection of acetaminophen increased by 13.8% when the SW30HR membrane was used. As mentioned previously in this section, the SW30HR membrane has an overall lower performance at pH 4 for all selected CECs; therefore, increase in rejection with an increase in pH value could be expected. However, an increase in operating pH to pH 7 led to a negative charge of the Desal-5 DK membrane surface, while the acetaminophen molecule keeps a positive charge (pKa > pH). Therefore, decrease in rejection value due to electrostatic attraction between acetaminophen and membrane surface could occur. Further increase in pH value to 10 resulted in an evident increase in rejection of acetaminophen by all three membranes (R > 78%). Hence, electrostatic repulsion between the negatively charged membrane surfaces and negatively charged acetaminophen (pKa < pH) contributed to increased rejection values. The greatest increase in rejection of acetaminophen with increase in operating pH (from 4 to 10) was observed when the NF270 membrane was used. Increase in rejection of acetaminophen by NF membranes with an increase in pH value was also observed in a previously published study [ 44 ]. Size exclusion and electrostatic interactions could be considered as the most important removal mechanisms by selected membranes, whereas, due to the acetaminophen hydrophilic nature, hydrophobic interactions had no noticeable impact on rejection. Membranes 2025,15, 358 16 of 20 Figure 4. Effect of sodium chloride addition on the rejection of selected CECs by the RO membrane SW30HR. Increased rejection values of clarithromycin and ofloxacin by RO membrane were observed with addition of sodium chloride to the feed solution. The increased rejection for positively charged clarithromycin and ofloxacin, and decreased rejection of negative charged CECs, contributed to the general mechanistic differentiation from charge screening as dominant sodium chloride effect. Sodium chloride affected primarily membrane negative charge rather than CEC charge screening. Electrostatic attraction between the SW30HR membrane surface and positively charged clarithromycin at pH 7 decreases due to suppressed membrane surface charge, consequently slightly increasing rejection. Furthermore, apparent 100% rejection values of carbofuran and malathion were observed with and without sodium chloride addition. Since ofloxacin and malathion are neutral at pH 7, decrease in membrane surface charge would not impact the rejection. Furthermore, based on SW30HR MWCO (100 Da) and the general usage in desalination processes, it could be expected to reach higher rejection values concerning all tested CECs (CECs MM > SW30HR MWCO). However, the obtained results, both with and without sodium chloride added, showed relevance of other mechanisms besides size exclusion which negatively affected total rejection values obtained when using SW30HR membrane. 4. Conclusions This study included the evaluation of NF and RO implementation for the removal of pharmaceuticals, pesticides, and PFAS (contaminants of emerging concern—CECs) from aqueous media at reported environmentally relevant concentrations, thereby addressing a critical gap in the current literature, which predominantly focuses on higher, non-environmental levels. Twelve compounds were selected based on their molecular descriptors (MM, pKa, and logK o/w ) with focus on covering a wide range of molecular properties. Rejection values ranged from 42.07% to apparent 100% by selected membranes and were greatly influenced by operating pH, MM, and pKa value. These findings demonstrated a different impact of evaluated molecular descriptors, reinforcing previously reported studies with CEC-specific analysis and mechanistic clarification. Higher operating pH values increased CECs rejection values when using the SW30HR and NF270 membranes; however, the operating pH impact on CECs rejection when using the Desal-5 DK membrane was not as clear. MM greatly influenced CECs’ rejection values at all pH values, whereas logK o/w values’ influence was rather minor. Electrostatic repulsion or electrostatic attraction strongly affected rejection values. Sodium chloride addition to the feed solution decreased rejection of eight selected CECs by the RO membrane. Size exclusion and electrostatic interactions were identified as the main removal mechanisms for selected PhACs, pesticides, and PFAS, with a lower influence of hydrophobic interactions. Future Membranes 2025,15, 358 17 of 20 research could validate reported findings in more complex natural matrices where organic matter, colloids, and competitive sorption could modify CECs–membrane interactions. Additionally, sufficiently large amount of obtained data opens possibilities for exploring data-driven modeling approaches to correlate process descriptors (operating conditions, membrane properties, and solute molecular characteristics) with performance outputs, such as rejection, which could provide valuable insights. Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/membranes15120358/s1. Figure S1: Rejection of selected CECs at three pH values by SW30HR, Desal-5 DK, and NF270 membranes; Method: UHPLC-MS/MS.; Table S1: Gradient profile—time, percentage of mobile phases and flow rate; Table S2: MS/MS parameters; Table S3: Recovery and RSD of selected CECs. Author Contributions: Conceptualization, N.M. and C.B.; formal analysis, I.A. and J.Ž.; investigation, J.Š., N.M. and C.B.; data curation, J.Š., N.M. and C.F.G.; writing—original draft preparation, J.Š.; writing—review and editing, N.M., C.F.G., N.Ð.-M., I.A., J.Ž., Z.Š. and J.G.C.; visualization, J.Š. and N.M.; supervision, N.Ð.-M., Z.Š. and J.G.C.; funding acquisition, N.Ð.-M. All authors have read and agreed to the published version of the manuscript. Funding: Funded by the European Union. Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or EU executive agency. Neither the European Union nor the granting authority can be held responsible for them. This work is conducted under the project TwiNSol-CECs that has received funding from Horizon Europe programme under grant agreement no. 101059867. Data Availability Statement: Data supporting reported results can be found at the following link: https://doi.org/10.5281/zenodo.15790703 (accessed on 2 November 2025). Conflicts of Interest: The authors declare no conflicts of interest. Abbreviations The following abbreviations are used in this manuscript: CECs Contaminants of emerging concern HLB Hydrophilic–lipophilic balance MeOH Methanol MM Molecular mass MWCO Molecular weight cut off NF Nanofiltration PFAS Polyand perfluoroalkyl substances PFBA Perfluorobutanoic acid PFBS Perfluorobutane sulfonic acid PFOA Perfluorooctanoate PFOS Perfluorooctane sulfonic acid PFOSA Perfluorooctane sulfonamide PhACs Pharmaceutically active compounds RO Reverse osmosis SPE Solid phase extraction TFC Thin-film composite UHPLC-MS/MS High performance liquid chromatography coupled with triple quadrupole mass spectrometry Membranes 2025,15, 358 18 of 20 References 1. Richardson, S.D.; Kimura, S.Y. 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