Microplastic contamination in wastewater: Sources, distribution, detection and remediation through physical and chemical-biological methods

Occurrence and environmental consequences of microplastics and nanoplastics from agricultural reuse of wastewater and biosolids in the soil ecosystem: A review

The contamination of soil and groundwater ecosystems by plastic particles (micro- and nanoplastics) was discussed, focusing on wastewater and biosolids recycled into agricultural soils. The impact of these contaminants was critically examined. Livestock (average: 18; min.: 8 - max.: 42 MP/L) and municipal (average: 2226; min: 0.08 - máx: 31,400 MP/L) wastewater, vinasse, and biosolids (>30,000 MP/L) from wastewater treatment plants are the most frequently reported in the literature for their nutritional potential in agricultural reuse. However, aside from municipal wastewater and biosolids, plastic particles in these other matrices are still largely unexplored, posing a potential threat to soil quality due to the limited understanding of their contribution to soil contamination. The particles accumulate in deeper layers, altering the hydraulic conductivity, fertility, organic matter availability, greenhouse gas emissions, and soil fauna and microorganisms. Nanoplastics have a more pronounced impact than microplastics and represent a greater threat. Due to their vertical mobility, nanoplastics have a greater capacity to accumulate in deep layers, including in groundwater. Different from what is observed for microplastics, current detection and quantification methodologies for nanoplastics are broad and nonspecific. It currently considers extensive size ranges (0-5000 μm), making it difficult to accurately identify these compounds, highlighting the need for more suitable methods for detecting nanoplastics. Given the recognized impacts on soil, it is essential to advance studies to ensure the benefits of reusing wastewater and organic soil amendments while effectively eliminating plastic particles from these matrices to prevent critical contamination scenarios.

Aerosols Generated in the Wastewater Treatment Process Are a Potential Source of Airborne Microplastics

Airborne microplastics pose a significant risk to human health. Similarly to the water-air transfer process, such as sea spray, aerosols generated during the wastewater treatment process, driven by aeration and mechanical agitation, are an overlooked potential source of airborne microplastics. This study constitutes the first attempt to investigate the pollution characteristics of microplastics in aerosols generated during wastewater treatment, based on laser direct infrared spectroscopy (LDIR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Microplastics were ubiquitously observed in aerosols from each unit of the wastewater treatment plant, with abundances in the range of 0.83-28.03 items·m-3. A total of 30 different polymer types were identified by LDIR, while polyvinyl chloride and polyethylene terephthalate were the most common polymers. Film and fragment were the main shapes, with a predominant size range of 20-50 μm. The aerosolization degree of microplastics is affected by the aeration intensities and hydrodynamic conditions maintained in each unit, but also varied depending on their inherent characteristics. These findings suggest that the aerosolization of microplastics from wastewater treatment is a potential source of airborne microplastics. This study contributes a novel insight into the occurrence of microplastics in aerosols generated during wastewater treatment.

Establishment and application of standard analysis methods for microplastic samples: Urban sewage and sewage sludge as a source of microplastics in the environment

The widespread use of plastics has led to the ubiquitous presence of microplastics (MPs) in the environment, posing risks to ecosystems and human health. Wastewater treatment plants (WWTPs), which often fail to completely remove MPs during treatment, have become a significant source of pollution. However, inconsistencies in sampling, pretreatment, and identification methods hinder comparative studies. This study developed a standardized method for MP analysis in WWTP water and sludge samples. Metal filters and ultrasound-assisted transfer improved desorption efficiency, while NaI flotation achieved nearly complete MP recovery. A two-step digestion method combining Fenton reagent and cellulase effectively removed organic matter (weight loss of 54.21 ± 2.00%) while maintaining 100% MP recovery. By tailoring the method to variables such as treatment processes, water volume, and pollution sources, a "gold standard" approach was designed to evaluate the environmental abundance of MPs in various WWTPs. Application of this method revealed MP concentrations of 2530-18,240 MP/L in influent and 650-1700 MP/L in effluent, with an estimated daily discharge of 1.42 × 108 MP/d into the environment. Primary sedimentation and skimming removed 57.07% of MPs, with secondary and advanced treatments enhancing removal. MPs primarily transferred to sludge, averaging 38.6-104.5 MP/g (dry weight). The most abundant MPs in influent were PU, PET, and PTFE, while PA, PU, and PET dominated in effluent. MPs smaller than 0.5 mm accounted for 98%, with regular particles increasing in effluent. This efficient method establishes a "gold standard" for MP analysis in WWTPs.

Aquatic insects as mediator for microplastics pollution in a river ecosystem of Bangladesh

Microplastics (MPs) are emerging pollutants that threaten the aquatic ecosystem. Aquatic insects may play a crucial role in moving MPs into different trophic levels within and across the ecosystems. However, field-level evidence is still insufficient globally despite its tremendous ecological significance. Thus, for the first time in Bangladesh, MPs were explored in six species of aquatic insects along with water and sediment of the Daleshwari River. Digestion and density separation methods were used for the extraction of MPs. Microscopic inspection and Fourier transform spectroscopy (FT-IR) were done to identify and quantify MPs. The average concentration of MPs in sediment and water is 143.1 ± 28.52 of MPs/L and 30153.8 ± 2313.62 of MPs/kg, respectively. In aquatic species, the highest MPs found in D. rusticus (57.82 ± 14.98 MPs/g), followed by B. contaminate (38.53 ± 6.87 MPs/g), Ranatra sp. (34.05 ± 5.39 MPs/g), C. servilia (26.99 ± 7.88 MPs/g), D. annulatus (16.44 ± 6.95 MPs/g), and O. sabina (14.13 ± 4.52 MPs/g). A total of eight types of polymers have been identified. It was important to notice that the studied aquatic insects bear similar MPs (size, shape, and color) found in water and sediments from the river. It reveals the potential for the insects (accumulators of MPs) to be a driving factor for the transport of the MPs across different ecosystems. It has also been found that Aquatic insect's size, weight, feeding habitat, and host reserviour could be responsible for MPs ingestion. In addition, ecological risk assessment (Contamination Factor, Nemerrow Pollution Index, Pollution Load Index, Polymer Hazard Index) indicates different levels of risk for the pertaining river ecosystem.

Microplastic proliferation in Malaysia's waterways: bridging knowledge gaps for environmental health

Microplastic (MP) pollution is an imperative environmental concern in Malaysia, distinguished by its insidious nature and enduring detrimental impacts. The nation grapples with challenges such as intensified industrial activities, inadequate plastic waste management, and insufficient law enforcement. There is an urgent need to address Malaysian waterways to mitigate this "Silent Killer" that compromises the food chain, with approximately 50% of MP ingestion attributed to fish, averaging 502.3 mg per individual daily. This review critically evaluates both primary and secondary sources of MP pollution within Malaysia's aquatic ecosystems, categorizing them into three distinct groups: (1) terrestrial sources, (2) aquatic sources, and (3) atmospheric sources. The regulatory frameworks and socioeconomic determinants, including the escalation of vehicle usage and industrial operations, inform these classifications. The research compilation utilized scientific databases, academic conferences, and sector-specific reports. The study underscores the paucity of information regarding MP pollution. It highlights the necessity for comprehensive investigations employing standardized methodologies and primary data collection, encompassing seafood samples, small streams, drainage systems, and sludge analysis. Additionally, secondary data sources, such as air samples from industrial precincts and aquatic environments, are essential for assessing MP. Raising public awareness about post-consumer plastic waste management and oil disposal in restaurants and workshops is crucial. Robust legal frameworks must be enacted and enforced across the nation, extending beyond urban locales, with stringent enforcement and standardized data gathering being vital for formulating effective strategies to reduce plastic waste and foster a safer ecological environment.

Risk assessment of potentially toxic elements, microplastics, and microorganisms in groundwater around municipal solid waste landfill

Risk assessment of potential toxic elements (PTEs), microplastics (MPs) and microorganisms in groundwater around landfills is critical. Waste from landfills seeps into groundwater contaminating water quality, threatening groundwater safety, and negatively affecting the ecosystem. This study explored spatial and temporal changes in PTEs, MPs, and microorganisms in the groundwater around a closed landfill. The results showed that Mn and Cr were the most predominant PTEs in the groundwater, average Mn and Cr concentrations in June being 1.16 and 4.51 times higher than in November, respectively. The Risk assessment of PTEs in groundwater Mn was heavily contaminated, Cr was moderately contaminated. The abundance of MPs the average value of MPs in June was 1.55 times higher than that in November; the MPs indicated that groundwater is more heavily contaminated, especially in the downstream areas. The Proteobacteria is the main phylum, and PLS-PM, PTEs were positively correlated with the phylum of microorganisms, negatively correlated with the genus of microorganisms and the abundance of MPs. This study emphasizes the importance of environmental management of landfills, provide new insights into the monitoring and identification of groundwater contamination as well as scientific guidance on appropriate remediation strategies for leachate-contaminated groundwater.

Effects of microplastics on polycyclic aromatic hydrocarbons migration in Baiyangdian Lake, northern China: Concentrations, sorption-desorption behavior, and multi-phase exchange

Microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) have been found in all environment matrices and are of concern worldwide. In this study, PAHs were determined in Baiyangdian Lake, China, and the effects of MPs on the migration of PAHs at the lake interfaces were analyzed. The average abundances of detected MPs were 9595 items m-3 for water and 1023 items kg-1 for sediment. The detected MPs were polyamide 6, polypropylene, polyethylene, and polyethylene terephthalate. The average Σ16PAHs in the water, sediment, and air were 1338 ng L-1, 751 ng g-1 dry weight, and 395 ng m-3, respectively. At the air-water interface, naphthalene, and phenanthrene volatilized from water to air, whereas benzo(b)fluoranthene, benzo(k)fluoranthene, and dibenzo(a,h)anthracene deposited from air to water. The fugacity fraction between sediment and bottom water ranged from 0.88 to 0.99, which indicated net volatilization at the water-sediment interface. The adsorption capacities of the four MPs for the PAHs ranged from 39.4 to 99.8 μg g-1 with a desorption efficiency range of 0.01%-44.3% under oscillation. According to the distribution of PAHs on the MPs, the exchange fluxes of PAHs at the water-air and sediment-water interfaces were recalculated. The results showed that the MPs could increase deposition of the PAHs from air to the water (ΔFA-W: -221 × 10-2 to -0.01 × 10-2 ng m-2 d-1) and the volatilization of PAHs from sediment to water (ΔFW-S: -79.7 × 105 to 180 × 105 ng m-2 d-1), which suggests that MPs increase the risk of PAHs in water and to aquatic organisms.

Assessment of potential ecological risk for microplastics in freshwater ecosystems

Microplastics (MPs) are one of the most widespread environmental pollutants, but their risk assessment to freshwater ecosystems has not been clearly investigated. Risk assessment has been constrained by the absence of MP concentration in some environment, the diverse types and shapes of MPs, and limitations of polystyrene (PS)-biased toxicity studies. This study examined exposure to MPs in rivers and lakes worldwide, including China (the Three Gorges Dam & Yangtze River (TGD & YR) and the lakes of Wuhan city (WL)), Vietnam (seven lakes of Da Nang city (7UL)), Europe (the Rhine River (RR)), Finland (Kallavesi Lake (KL)), Argentina (nine lakes in the Patagonia region (9LP)), Brazil (Guaiba Lake (GL)), and South Korea (Nakdong River (NR), Han River (HR), and Anyang Stream (AS)), and assessed the risks to aquatic ecosystems based on the toxicity information and morphology of MPs. We also examine the limitations of the traditional risk quotient (RQ)-based risk assessment method for PS-biased toxicity studies. Potential ecological risks were assessed using pollution load index (PLI) and potential ecological risk index (PERI) considering the hazard scores of MP types. RQ was approximately 10-6 to 10-4, indicating negligible risk to aquatic organisms. In contrast, the calculated PLI (>30: extreme danger) and PERI (>1200: extreme danger) values suggest that MPs represent serious ecological threats at all the study locations. Furthermore, principal component analysis (PCA) indicated that MP fibers and fragments have a significant impact on the risks for freshwater systems. These MP morphologies derive from surrounding fishing and agricultural activities, and household and clothing industries. The areas surrounding these rivers and lakes are expected to become more densely populated, potentially leading to increased MP emissions and higher risks, suggesting a need to expand wastewater treatment facilities, reduce consumption of single-use plastics, and raise societal awareness of waste plastics.

A review of methods for mitigating microplastic contamination in biosolids from wastewater treatment plants before agricultural soil application

Wastewater treatment plants (WWTP) are recognized as major sources of microplastic (MP) particles in terrestrial environments, particularly in agricultural soils through biosolids application. While many reviews have focused on the distribution, detection, and mitigation of MPs in wastewater effluent to limit their discharge into oceans, our understanding of methods to mitigate biosolid contamination remains limited. This review focuses on methods for mitigating MPs contamination in biosolids at various intervention points, including sources, WWTP including the primary and secondary treatment stages where sludge is generated, and post-contamination. These methods are categorized as physical, physicochemical, and biological approaches, and their advantages and limitations are discussed. For instance, physicochemical methods, especially froth flotation, are cost-effective but are hindered by contaminants and reagents. Physical methods like microfibre filtration devices (MFD) are safe but their efficiency depends on the filter pore size and design. Biological methods, particularly microbial degradation, are limited by the varying efficiencies of microorganisms in breaking down MPs and the extended time required for their effective degradation. Other physical methods including dissolved air flotation, and ultrasonication already exist in WWTPs but may require retrofitting or optimization to enhance MP removal from biosolids. As each method inherently has limitations, the key to achieving MP-free biosolids, and thus preventing their release into agricultural soil, lies in integrating these methods through multi-coupling strategies.

Determination of Seasonal Microplastic pollutıon Variation in Aquatic Environments: Case Study from İskenderun Technical University Pond

Although microplastic (MP) pollution in aquatic ecosystems has been a critical issue, a significant portion of previous studies has been limited to marine environments. Few studies have evaluated MP abundance in inland waters, and those that exist often ignore seasonal variations. This study aimed to assess the seasonal variations in microplastic (MP) abundance in the İskenderun Technical University (İSTE) Pond. MP abundance ranged from 0.5 MPs/L to 10.8 MPs/L, with a mean of 3.7 MPs/L. Fiber-shaped, black-colored, small-sized (< 1000 μm) MPs were commonly found on the surface water. Statistical analysis confirmed significant variations in MP abundance across seasons. The abundance of MPs in the surface water correlated with the mean annual precipitation. Atmospheric deposition and storm water runoff were major contributors to microplastic pollution in the pond. PP and PET particles were identified. The findings of this study contains preliminary results that can be used in the development of future legislations and regulations.

Effects of particle size and aging on heavy metal adsorption by polypropylene and polystyrene microplastics under varying environmental conditions

Microplastics have become a major environmental issue because of their widespread presence and tendency to adsorb heavy metals, which can have harmful effects on aquatic ecosystems and human health. The present study investigates the adsorption mechanisms of Pb2+ and Cu2+ ions on both pristine and artificially aged microplastics (MPs) made of polystyrene (PS) and polypropylene (PP). Furthermore, the influence of MP size on the adsorption capacity under different environmental conditions was evaluated. According to the characterization of MPs, aging leads to physical damage and an increase in the number of oxygen-containing functional groups on their surface. The experimental results highlight the significantly higher adsorption ability of smaller and aged MPs compared with that of pristine MPs for both the heavy metal ions. The pseudo-second-order equation provided a better fit for the adsorption kinetics study (R2 = 0.95), suggesting that chemisorption governs the rate-limiting phase in the adsorption mechanism on the MP surfaces. The concordance between the adsorption isotherm model and Freundlich model (R2 > 0.95) indicated a predominance of multilayer adsorption. The environmental factors such as pH, humic acid, temperature, and SO42- concentration significantly affected the adsorption of Pb2⁺ and Cu2⁺ onto PP and PS MPs. These variables play a crucial role in determining the nature of the interactions between heavy metal ions and the microplastic particles under diverse environmental conditions. Electrostatic interactions, surface complexation and van der Waals forces were identified as two factors that could either improve or diminish the metal ion adsorption capacity of MPs.

Applications of the Microalgae Chlamydomonas and Its Bacterial Consortia in Detoxification and Bioproduction

The wide metabolic diversity of microalgae, their fast growth rates, and low-cost production make these organisms highly promising resources for a variety of biotechnological applications, addressing critical needs in industry, agriculture, and medicine. The use of microalgae in consortia with bacteria is proving valuable in several areas of biotechnology, including the treatment of various types of wastewater, the production of biofertilizers, and the extraction of various products from their biomass. The monoculture of the microalga Chlamydomonas has been a prominent research model for many years and has been extensively used in the study of photosynthesis, sulphur and phosphorus metabolism, nitrogen metabolism, respiration, and flagellar synthesis, among others. Recent research has increasingly recognised the potential of Chlamydomonas-bacteria consortia as a biotechnological tool for various applications. The detoxification of wastewater using Chlamydomonas and its bacterial consortia offers significant potential for sustainable reduction of contaminants, while facilitating resource recovery and the valorisation of microalgal biomass. The use of Chlamydomonas and its bacterial consortia as biofertilizers can offer several benefits, such as increasing crop yields, protecting crops, maintaining soil fertility and stability, contributing to CO2 mitigation, and contributing to sustainable agricultural practises. Chlamydomonas-bacterial consortia play an important role in the production of high-value products, particularly in the production of biofuels and the enhancement of H2 production. This review aims to provide a comprehensive understanding of the potential of Chlamydomonas monoculture and its bacterial consortia to identify current applications and to propose new research and development directions to maximise their potential.

The Microalgae Chlamydomonas for Bioremediation and Bioproduct Production

The extensive metabolic diversity of microalgae, coupled with their rapid growth rates and cost-effective production, position these organisms as highly promising resources for a wide range of biotechnological applications. These characteristics allow microalgae to address crucial needs in the agricultural, medical, and industrial sectors. Microalgae are proving to be valuable in various fields, including the remediation of diverse wastewater types, the production of biofuels and biofertilizers, and the extraction of various products from their biomass. For decades, the microalga Chlamydomonas has been widely used as a fundamental research model organism in various areas such as photosynthesis, respiration, sulfur and phosphorus metabolism, nitrogen metabolism, and flagella synthesis, among others. However, in recent years, the potential of Chlamydomonas as a biotechnological tool for bioremediation, biofertilization, biomass, and bioproducts production has been increasingly recognized. Bioremediation of wastewater using Chlamydomonas presents significant potential for sustainable reduction in contaminants and facilitates resource recovery and valorization of microalgal biomass, offering important economic benefits. Chlamydomonas has also established itself as a platform for the production of a wide variety of biotechnologically interesting products, such as different types of biofuels, and high-value-added products. The aim of this review is to achieve a comprehensive understanding of the potential of Chlamydomonas in these aspects, and to explore their interrelationship, which would offer significant environmental and biotechnological advantages.

Microplastics removal in wastewater treatment plants: A review of the different approaches to limit their release in the environment

In last 10 years, the interest about the presence of microplastics (MPs) in the environment has strongly grown. Wastewaters function as a carrier for MPs contamination from source to the aquatic environment, so the knowledge of the fate of this emerging contaminant in wastewater treatment plants (WWTPs) is a priority. This work aims to review the presence of MPs in the influent wastewater (WW) and the effectiveness of the treatments of conventional WWTPs. Moreover, the negative impacts of MPs on the management of the processes have been also discussed. The work also focuses on the possible approaches to tackle MPs contamination enhancing the effectiveness of the WWTPs. Based on literature results, despite WWTPs are not designed for MPs removal from WW, they can effectively remove the MPs (up to 99 % in some references). Nevertheless, they normally act as "hotspots" of MPs contamination considering the remaining concentration of MPs in WWTPs' effluents can be several orders of magnitude higher than receiving waters. Moreover, MPs removed from WW are concentrated in sewage sludge (potentially >65 % of MPs entering the WWTP) posing a concern in case of the potential reuse as a soil improver. This work aims to present a paradigm shift intending WWTPs as key barriers for environmental protection. Approaches for increasing effectiveness against MPs have been discussed in order to define the optimal point(s) of the WWTP in which these technologies should be located. The need of a future legislation about MPs in water and sludge is discussed.

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Toxicological review of micro- and nano-plastics in aquatic environments: Risks to ecosystems, food web dynamics and human health

The increase of micro- and nano-plastics (MNPs) in aquatic environments has become a significant concern due to their potential toxicological effects on ecosystems, food web dynamics, and human health. These plastic particles emerge from a range of sources, such as the breakdown of larger plastic waste, consumer products, and industrial outputs. This review provides a detailed report of the transmission and dangers of MNPs in aquatic ecosystems, environmental behavior, and interactions within aquatic food webs, emphasizing their toxic impact on marine life. It explores the relationship between particle size and toxicity, their distribution in different tissues, and the process of trophic transfer through the food web. MNPs, once consumed, can be found in various organs, including the digestive system, gills, and liver. Their consumption by lower trophic level organisms facilitates their progression up the food chain, potentially leading to bioaccumulation and biomagnification, thereby posing substantial risks to the health, reproduction, and behavior of aquatic species. This work also explores how MNPs, through their persistence and bioaccumulation, pose risks to aquatic biodiversity and disrupt trophic relationships. The review also addresses the implications of MNPs for human health, particularly through the consumption of contaminated seafood, highlighting the direct and indirect pathways through which humans are exposed to these pollutants. Furthermore, the review highlights the recommendations for future research directions, emphasizing the integration of ecological, toxicological, and human health studies to inform risk assessments and develop mitigation strategies to address the global challenge of plastic pollution in aquatic environments.

In Situ Electrochemical Synthesis of Squamous-like Cu2S Induced by Sulfate-Reducing Bacteria as a Fenton-like Catalyst in Wastewater Treatment: Catalytic Performance and Mechanism

In this paper, a novel method was proposed for the synthesis of Cu2S on copper mesh via electrolysis in SRB culture medium. It was found that following electrolysis in SRB medium, squamous-like Cu2S arrays were obtained on the copper mesh, and the Cu2S loading contents varied with the electrolyzing parameters. The resultant Cu2S on copper mesh in SRB (CSCM-SRB) with the highest catalytic MB degradation properties was produced by electrolysis at 3.75 mA/cm2 for 900 s. The optimized MB-degrading conditions were determined to be 1.2 cm2/mL CSCM-SRB with 0.05 M H2O2 at 35 °C when pH = 6, under which the degradation of MB reached over 99% after 120 min of reaction. Disinfecting properties was also proven by antibacterial tests, revealing that an almost 100% antibacterial rate against E. coli was obtained after 8 min. The organic compounds produced by SRB adsorbed on CSCM-SRB strongly promoted the degradation of MB. Furthermore, possible Fenton-like mechanisms of CSCM-SRB were proposed, illustrating that ·O2-, ·OH, and 1O2 acted as the main functional species during Fenton-like reactions, leading to effective MB degradation and high antibacterial properties. Finally, a simple device for wastewater treatment was designed, providing possible applications in real environments.