Key Takeaways & Executive Findings
- •• • Adsorption kinetics for all four microplastics (PE, PP, PS, PVC) toward diazepam, fluoxetine, and mianserin conformed to a pseudo-second-order model, indicating chemisorption as the rate-limiting step; this implies that microplastic-drug interactions are not merely physical but involve specific chemical forces, affecting the reversibility and potential release in the environment. • • PE exhibited the highest adsorption capacity for fluoxetine, PP for mianserin, and PVC for diazepam, with Langmuir and Freundlich model fits exceeding 0.9; this selectivity suggests that polymer type dictates the dominant adsorption mechanism (e.g., hydrophobic partitioning for PE/PP, polar interactions for PVC), which is critical for predicting contaminant transport in polymer-specific waste streams. • • Diazepam adsorption on microplastics was maximal at pH 6.5–8.5, the typical pH range of natural surface waters, and decreased under acidic or alkaline conditions due to electrostatic repulsion; this pH dependency implies that environmental pH fluctuations can modulate the bioavailability and mobility of psychoactive drugs, with potential implications for aquatic toxicity. • • Increasing NaCl concentration enhanced diazepam adsorption, with equilibrium adsorption capacity rising as ionic strength increased; this salting-out effect, driven by non-electrostatic interactions, indicates that in marine or brackish environments, microplastics may act as stronger sinks for such contaminants, altering their fate and transport.
Abstract
Microplastics, as emerging environmental pollutants, can adsorb psychotropic drugs in aquatic environments, facilitating their migration and transformation, ultimately posing ecological risks. This study investigated the adsorption behavior and mechanisms of four common microplastics—polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC)—each with a particle size of 50 μm, toward three psychoactive drugs: diazepam, fluoxetine, and mianserin. Adsorption kinetics, isotherms, and the effects of pH and salinity were examined. Kinetic data fitted well to a pseudo-second-order model, indicating chemisorption as the rate-limiting step. Isotherm analysis using Langmuir and Freundlich models revealed that PE exhibited the highest affinity for fluoxetine, PP for mianserin, and PVC for diazepam, while PS showed linear adsorption for fluoxetine, suggesting partitioning. The adsorption of diazepam was maximal at pH 6.5–8.5, typical of natural surface waters, and increased with NaCl concentration, indicating that non-electrostatic interactions dominate and that higher ionic strength enhances adsorption. Mechanistic insights suggest that hydrophobic interactions, hydrogen bonding, π-π interactions (for PS), and halogen bonding (for fluoxetine) contribute to adsorption. These findings highlight the potential of microplastics to act as vectors for psychoactive drugs, necessitating further research on their environmental fate and ecological implications.
1. Introduction
The global rise in pharmaceutical consumption has led to the pervasive presence of psychoactive drugs in aquatic environments, with conventional wastewater treatment often achieving removal efficiencies below 50% for compounds like diazepam and fluoxetine. These recalcitrant pollutants, detected at concentrations up to 5.2 μg/L and 8.9 μg/L in effluent, respectively, pose ecological risks to non-target organisms. The COVID-19 pandemic exacerbated this issue, with prescriptions for anxiolytics and antidepressants surging by 30–50%, leading to elevated environmental inputs and risk quotients exceeding 0.1 in surface waters. Microplastics, ubiquitous in water bodies, exhibit high specific surface areas (50–100 m²/g) and hydrophobic surfaces, enabling them to adsorb organic contaminants and act as vectors for long-range transport. However, existing studies have largely focused on single polymer types or limited drug classes, leaving a critical gap in understanding the systematic interactions between diverse microplastics and multiple psychoactive drugs, particularly the tricyclic antidepressant mianserin.
This study addresses this bottleneck by systematically investigating the adsorption behavior of four common microplastics (PE, PP, PS, PVC) toward three psychoactive drugs (diazepam, fluoxetine, mianserin) under controlled conditions. By employing adsorption kinetics, isotherm modeling, and examining the influence of pH and salinity, we elucidate the underlying mechanisms, including hydrophobic partitioning, electrostatic interactions, hydrogen bonding, and π-π interactions. The findings provide essential data for assessing the environmental fate of these contaminants and inform risk assessment frameworks for microplastic-associated pharmaceutical pollution.
Loading authentic research manuscript (Pages 1–5)...
WANG Ruixue, WANG Yuqi, ZHANG Chenglong, XU Yunyun (2026). Adsorption Behavior of Microplastics for Typical Psychoactive Drugs. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202606014
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What are the dominant adsorption mechanisms for each microplastic type, and how do they influence the desorption potential in natural waters?
PE and PP primarily adsorb via hydrophobic partitioning and van der Waals forces, with hydrogen bonding contributing for polar drugs. PS enhances adsorption through π-π interactions due to its benzene rings, while PVC's chlorine atoms increase polarity, promoting dipole-dipole interactions. Fluoxetine can form carbon-halogen bonds with PVC, further strengthening adsorption. These mechanisms suggest that desorption may be slow under ambient conditions, but changes in pH or ionic strength could trigger release, as seen with diazepam's reduced adsorption at extreme pH.
How does the adsorption capacity of these microplastics compare to that of natural sediments or other sorbents, and what are the implications for risk assessment?
The study did not directly compare with natural sediments, but microplastics' high specific surface area (50–100 m²/g) and hydrophobic surfaces typically result in adsorption capacities exceeding those of natural particles. For instance, PE adsorbed fluoxetine effectively, with Langmuir fits above 0.9. This implies that microplastics can concentrate psychoactive drugs, potentially increasing their bioavailability to organisms that ingest microplastics, thereby amplifying ecotoxicological risks.
What is the effect of pH on adsorption, and why is the maximum observed at pH 6.5–8.5?
At pH 6.5–8.5, the surface charge of microplastics and the ionization state of diazepam (pKa ~3.4) result in minimal electrostatic repulsion, allowing hydrophobic and hydrogen bonding interactions to dominate. Outside this range, electrostatic repulsion between similarly charged surfaces and drug molecules reduces adsorption. This pH dependency is critical for predicting adsorption in natural waters, which typically fall within this optimal range, suggesting that microplastics will effectively scavenge diazepam in most freshwater systems.
How does salinity influence adsorption, and what does this imply for estuarine or marine environments?
Increasing NaCl concentration enhanced diazepam adsorption, attributed to the salting-out effect, which reduces the solubility of hydrophobic organic compounds and promotes their partitioning onto microplastics. This indicates that in saline waters, microplastics may exhibit higher adsorption capacities for such drugs, potentially increasing their persistence and transport in marine environments. The study found that non-electrostatic interactions dominate, so ionic strength primarily affects the aqueous activity coefficient rather than surface charge.
What are the limitations of this study in terms of environmental relevance, and what future research is needed?
This study used pristine microplastics of uniform size (50 μm) and single-drug solutions, which may not fully represent real-world conditions where microplastics are weathered, biofouled, and coexist with multiple contaminants. Future research should investigate the effects of aging, natural organic matter, and mixture toxicity. Additionally, the adsorption kinetics and isotherms were conducted under controlled laboratory conditions; field validation is necessary to confirm the findings under dynamic environmental conditions.
Related Chinese Research & Cross-Citations
Synergistic Regulation by Long- and Short-Chain Quorum Sensing Signaling Molecules Enhances Sulfamethoxazole Metabolism in Electroactive Biofilms within a Microbial Electrolysis Cell Coupled Anaerobic Digestion System
High-strength sulfamethoxazole (SMX) wastewater severely inhibits anaerobic microorganisms, reducing organic degradation and methane yield. This study investigated the effects of short-chain (C6-HSL) and long-chain (C12-HSL) N-acyl-homoserine lactone (AHL) signaling molecules, individually and in combination, on the construction, performance, and antibiotic resistance gene (ARG) profiles of anaerobic electroactive biofilms within a microbial electrolysis cell coupled anaerobic digestion (MEC-AD) system. Compared to the control (no AHLs), SMX removal efficiency increased by 9.26%, 7.44%, and 10.67% for C6-HSL (T1), C12-HSL (T2), and combined (T3) treatments, respectively. Methane production rates rose by 20.4%, 16.9%, and 23.1% for T1, T2, and T3, respectively. AHLs promoted extracellular polymeric substance secretion, enhancing electroactive microbe attachment to the anode. Microbial community analysis revealed increased diversity and modulated key functional genera. Notably, Georgenia abundance increased by 16.77% (T1) and 36.47% (T3) but decreased by 15.99% (T2). ARG analysis showed that single AHLs elevated intI1, sul1, and sul2 abundances, whereas combined AHLs (T3) exhibited a milder response, with sul2 abundance reduced by 4.92% relative to control. This suggests synergistic AHLs suppress ARG host proliferation. This study first demonstrates that combined short- and long-chain AHLs enhance electroactive biofilm formation, maintain microbial community stability, and modulate ARG dissemination risk, offering a quorum sensing-based strategy for antibiotic wastewater treatment and risk management.
Preparation of Solid-Phase Carbon Sources with Different Ratios and Their Carbon Release Properties
Low C/N ratios in wastewater treatment plant effluent necessitate external carbon sources for denitrification, but conventional liquid carbon sources are costly and unstable. This study prepared nine composite solid-phase carbon sources by combining PHBV with natural cellulose materials (straw, sawdust, corncob) at different mass ratios. Dynamic release experiments, DOC analysis, UV-Vis spectroscopy, and EEM fluorescence were employed to characterize carbon release. Results showed that increasing cellulose proportion in corncob-based sources led to release patterns opposite to those of straw- and sawdust-based sources. For straw and sawdust, higher cellulose ratios accelerated release rates, increased total release and duration, reduced aromaticity and molecular weight of released DOM, and promoted protein-like components (tryptophan, tyrosine), indicating enhanced bioavailability. Under identical ratios, corncob-based sources exhibited moderate total release, release durations exceeding 134 h, lower DOM aromaticity and molecular weight, and lower humic substance proportion, indicating superior bioavailability and engineering potential. Among the nine sources, JG5, MX5, and CC4 (PHBV:cellulose mass ratios of 4:5, 4:5, and 1:1, respectively) showed optimal comprehensive performance with low theoretical maximum release, long release periods, and high mass transfer coefficients. EEM-PARAFAC identified three DOM components (protein-like C1, C2; humic-like C3), with protein-like components dominating. This study validates the relationship between cellulose proportion and release kinetics and reveals synergistic regulation of DOM components, offering guidance for designing effective solid-phase carbon sources.
Enhancement of Anaerobic Digestion Operational Efficiency for Guar Gum Production Wastewater Using a Microaerobic-Biochar Coupled System
Guar gum production wastewater contains 1,2-propanediol, which in conventional anaerobic treatment causes propionate accumulation and microbial inhibition. Microaerobic conditions foster fermentative bacterial metabolism, enhancing organic substrate conversion, while biochar promotes anaerobic microbial aggregation and oxygen tolerance. This study treated actual guar gum wastewater using three configurations: blank control, anaerobic, and microaerobic-biochar (O2/BC) coupled systems. Under mesophilic conditions (37 °C), with micro-aeration at 0.2 mL/(g VS·d) and biochar dosage of 15 g/L, the O2/BC system achieved a COD removal efficiency of 90%, 10.6 percentage points higher than the anaerobic control. Effluent COD and propionate concentrations dropped to 3800 mg/L and 0.15 g/L, respectively, representing reductions of 49.6% and 98.4% versus the control. Biogas production was 1.64 times that of the control, with a maximum methane concentration of 77.2%. Fourier transform infrared spectroscopy (FT-IR) indicated increased abundance of –OH, –CH2–, and C–O functional groups on sludge surfaces, revealing biochar's adsorption enhancement. Scanning electron microscopy (SEM) showed dense microbial aggregates dominated by long bacilli, distinct from conventional anaerobic sludge. Microbial community analysis revealed increased abundance of Clostridium and Comamonas, modulating the propionate-to-acetate ratio and optimizing acidification efficiency, thereby promoting complex organic degradation. This study provides a novel technical pathway for biological treatment of alcohol-rich organic wastewater.
Occurrence Characteristics, Source Apportionment, and Ecological Risk Assessment of Pesticides in Plateau Lakes: A Case Study of Dianchi Lake
This study systematically investigated the occurrence, spatial distribution, sources, and ecological risks of 160 pesticides in Dianchi Lake, a typical plateau lake impacted by agricultural activities. A total of 37 pesticides were detected in the water, with total concentrations ranging from 64.2 to 1132.8 ng/L (average 610.0 ng/L). Fungicides, including boscalid (BOS), fluopicolide (FPC), and dimethomorph (DMM), were dominant, contributing up to 65.0% of the total concentration. Spatially, the southern lake region exhibited significantly higher concentrations (672.5 ng/L) than the north, attributed to intensive facility agriculture. Highly hydrophobic pesticides, such as penconazole (PEN), showed a tendency to enrich in bottom layers. Source apportionment identified inflowing rivers and wastewater treatment plant effluents as primary input sources, with average concentrations 7 and 9 times higher than lake water, respectively. Ecological risk assessment revealed that pesticides posed the highest risk to algae, followed by daphnia and fish. Prometryn (PMT) was identified as a high-risk factor for algae, while profenofos (PFF) and carbendazim (CBD) posed potential threats to higher trophic levels. These findings provide fundamental data and technical support for understanding pesticide pollution in plateau lake ecosystems.
Microbiome Mechanisms of Composite Carbon Sources for Enhancing Denitrification and Reducing N2O Emissions
Biological nitrogen removal in wastewater treatment plants (WWTPs) is often limited by insufficient influent carbon sources, necessitating external carbon addition to enhance denitrification. Conventional single carbon sources, such as sodium acetate, frequently fail to meet the metabolic demands of complex microbial communities, compromising nitrogen removal efficiency and stability. Composite carbon sources, by providing multiple electron donors, can improve metabolic cooperation among microorganisms, yet their underlying microbial mechanisms remain insufficiently understood. In this study, activated sludge from a municipal WWTP was used to investigate the microbial mechanisms of composite carbon sources during denitrification. Batch denitrification experiments were conducted in combination with metagenomic and metatranscriptomic analyses to systematically characterize microbial community structure and functional gene expression under different carbon source conditions. Results showed that, compared with sodium acetate as the single carbon source, the composite carbon source system (sodium acetate: sodium succinate: ethanol = 2:1:3) increased the denitrification rate from (6.822 ± 0.141) mg/(L·h) to (8.370 ± 0.186) mg/(L·h), representing a 22.7% improvement, while reducing N2O accumulation by approximately 55%. Metagenomic analysis revealed that Ottowia, Rubrivivax, Thauera, and Zoogloea were the dominant denitrifying genera. Metatranscriptomic results further demonstrated that the composite carbon sources significantly upregulated the transcription of key denitrification genes, with nirS, norB, and nosZ increasing by 37.8%, 27.4%, and 48.6%, respectively. In addition, the composite carbon sources promoted complementary carbon metabolic strategies among different microbial communities, enhancing electron donor supply and improving denitrification efficiency. These findings indicate that composite carbon sources synergistically enhance denitrification performance through regulation of functional gene transcription in complex microbial communities, providing a theoretical basis for carbon source optimization in WWTPs.
Key Environmental Behaviors and Pollution Control Strategies of Tire Wear Particles in Aquatic Environments
Tire wear particles (TWPs) are emerging pollutants and constitute the dominant type of microplastics (MPs) in urban stormwater runoff, accounting for up to 90% of MPs in some cases. They are characterized by small size, high mobility, complex composition, and significant toxicity. Current research on TWPs remains fragmented, lacking a comprehensive understanding of their environmental behaviors and pollution control in aquatic systems. This review systematically analyzes the enrichment and vectoring roles of TWPs for coexisting pollutants, and their environmental fate, including ecotoxicological impacts, detection methodologies, release of intrinsic additives, and aggregation and sedimentation behaviors. Drawing on insights from other microplastic studies, the paper explores control technologies across the pollution pathway—source, transport, and terminal treatment—and proposes feasible management strategies. Key findings indicate that TWPs can adsorb heavy metals and organic contaminants, with adsorption capacities influenced by aging processes. Their aggregation is governed by solution chemistry, with critical coagulation concentrations varying with ionic strength and pH. The release of additives such as zinc and benzothiazoles is significant, posing ecological risks. Future research should focus on real-water aggregation mechanisms, additive release under natural conditions, long-term performance of treatment facilities like constructed wetlands under TWPs stress, enzymatic degradation pathways, and integration of AI, big data, and IoT for cost-effective detection and risk modeling. This review provides a scientific basis for developing targeted pollution control measures for TWPs in aquatic environments.