Key Takeaways & Executive Findings
- •• • PE release rate (26.1±1.8%) significantly exceeds PP (16.4±1.3%) under 6-month simulated rainfall at 0.2% abundance and 20–40 μm size, indicating polymer-specific mobility that dictates environmental exposure risk. • • MPs of 40–60 μm size exhibit the highest release and vertical migration, while excessive abundance triggers aggregation and suppresses release, highlighting a critical size-abundance threshold for transport prediction. • • Vertical migration peaks between 14–18 months under 24-month simulated rainfall, with PE migrating deeper than PP, underscoring the long-term contamination potential of sludge-amended soils. • • Environmental factors exert decisive control: migration increases with pH but decreases with electrolyte concentration; sludge leachate promotes transport at low organic matter concentrations but inhibits at high concentrations, necessitating site-specific risk assessments.
Abstract
Microplastic pollution poses a severe threat to terrestrial ecosystems, with soil acting as a major sink. The application of sewage sludge organic fertilizer in public green spaces introduces microplastics (MPs) into the soil, yet their release and vertical migration dynamics remain poorly understood. This study investigated the release and transport of polypropylene (PP) and polyethylene (PE) MPs, the most prevalent types in sludge organic fertilizer, under simulated rainfall conditions representative of Chengdu. Over a six-month simulated rainfall period, the release rate of PE (26.1±1.8%) at 0.2% abundance (weight ratio) and 20–40 μm size was significantly higher than that of PP (16.4±1.3%). The highest release was observed for 40–60 μm particles, while excessive abundance induced aggregation, inhibiting release. A 24-month simulated transport experiment revealed that PE exhibited higher mobility than PP, with peak migration occurring between 14 and 18 months, and 40–60 μm particles showing the greatest transport capacity. Environmental factors critically modulated migration: increasing pH enhanced mobility, but the promoting effect of sludge leachate diminished under alkaline conditions; higher electrolyte concentrations reduced mobility, with sludge leachate exerting stronger inhibition at high EC; organic matter exhibited a non-linear effect, promoting transport at low concentrations and inhibiting at high concentrations. These findings provide essential data for mitigating microplastic contamination in public green spaces.
1. Introduction
Microplastic contamination of agricultural and urban soils has emerged as a critical environmental challenge, with sewage sludge organic fertilizer serving as a primary entry vector. While sludge recycling offers a sustainable solution for waste management, it inadvertently introduces microplastics into terrestrial ecosystems, where they accumulate and potentially migrate to groundwater. Existing studies have documented microplastic presence in sludge, yet the dynamic processes governing their release from organic matrices and subsequent vertical transport under realistic rainfall conditions remain inadequately quantified. This knowledge gap hinders accurate risk assessment and the development of effective mitigation strategies for public green spaces.
This investigation addresses this bottleneck by systematically evaluating the release and vertical migration of polypropylene (PP) and polyethylene (PE) microplastics from sludge organic fertilizer under simulated rainfall. By quantifying release rates over a six-month fertilization cycle and transport dynamics over 24 months, the study delineates the influence of particle size, abundance, and key environmental parameters (pH, electrolyte concentration, organic matter). The findings reveal polymer-specific behaviors and non-linear responses to environmental factors, providing a robust empirical foundation for predicting microplastic fate and informing regulatory frameworks for sludge reuse in urban landscaping.
Loading authentic research manuscript (Pages 1–5)...
WU Bi, WU Zheng, HUANG Tao (2026). Release and Vertical Migration Behavior of Typical Microplastics from Sewage Sludge Organic Fertilizer Applied in Public Green Spaces. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607015
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 relative release rates of PE and PP from sludge organic fertilizer under simulated rainfall, and how do they vary with particle size?
Under six months of simulated rainfall, PE exhibits a release rate of 26.1±1.8% at 0.2% abundance and 20–40 μm size, significantly higher than PP's 16.4±1.3%. The highest release occurs for 40–60 μm particles, while smaller (20–40 μm) and larger (>60 μm) sizes show lower release due to aggregation and kinetic inertia, respectively.
How does the vertical migration of microplastics evolve over a 24-month period, and what is the peak migration window?
Vertical migration of microplastics from sludge organic fertilizer occurs over extended periods, with peak transport observed between 14 and 18 months of simulated rainfall. PE migrates more readily than PP, and 40–60 μm particles exhibit the greatest mobility, reaching deeper soil layers.
What is the impact of environmental pH on microplastic transport, and how does sludge leachate modulate this effect?
Microplastic transport capacity increases with rising pH. Under alkaline conditions, the promoting effect of sludge leachate on transport diminishes, as the leachate's pH is higher than the ambient medium, and high pH itself enhances mobility.
How do electrolyte concentration and organic matter content in the soil solution influence microplastic migration?
Higher electrolyte concentrations reduce microplastic transport, with sludge leachate exerting stronger inhibition at high EC due to its elevated ionic strength. Organic matter exhibits a non-linear effect: at concentrations below that of sludge leachate, it promotes transport, while at higher concentrations, it inhibits migration.
What are the implications of these findings for the management of sludge organic fertilizer application in public green spaces?
The results indicate that microplastic release and migration are influenced by polymer type, particle size, and environmental conditions. To minimize soil contamination, application strategies should consider sludge characteristics and site-specific soil pH, salinity, and organic matter content. Monitoring and mitigation efforts should focus on the 40–60 μm size fraction and account for the enhanced mobility of PE over PP.
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.