Wastewater treatment plant effluent as a source of microplastics: review of the fate, chemical interactions and potential risks to aquatic organisms

Macro- and Microplastics in the Antarctic Environment: Ongoing Assessment and Perspectives

The number of scientists and tourists visiting Antarctica is on the rise and, despite the management framework for environmental protection, some coastal areas, particularly in the Antarctic Peninsula region, are affected by plastic contamination. The few data available on the occurrence of microplastics (<5 mm) are difficult to compare, due to the different methodologies used in monitoring studies. However, indications are emerging to guide future research and to implement environmental protocols. In the surface and subsurface waters of the Southern Ocean, plastic debris >300 µm appears to be scarce and far less abundant than paint chips released from research vessels. Yet, near some coastal scientific stations, the fragmentation and degradation of larger plastic items, as well as microbeads and microfibers released into wastewater from personal care products and laundry, could potentially affect marine organisms. Some studies indicate that, through long-range atmospheric transport, plastic fibers produced on other continents can be deposited in Antarctica. Drifting plastic debris can also cross the Polar Front, with the potential to carry alien fouling organisms into the Southern Ocean. Sea ice dynamics appear to favor the uptake of microplastics by ice algae and Antarctic krill, the key species in the Antarctic marine food web. Euphausia superba apparently has the ability to fragment and expel ingested plastic particles at the nanoscale. However, most Antarctic organisms are endemic species, with unique ecophysiological adaptations to extreme environmental conditions and are likely highly sensitive to cumulative stresses caused by climate change, microplastics and other anthropogenic disturbances. Although there is limited evidence to date that micro- and nanoplastics have direct biological effects, our review aims at raising awareness of the problem and, in order to assess the real potential impact of microplastics in Antarctica, underlines the urgency to fill the methodological gaps for their detection in all environmental matrices, and to equip scientific stations and ships with adequate wastewater treatment plants to reduce the release of microfibers.

Wastewater treatment plant effluent and microfiber pollution: focus on industry-specific wastewater

The production, use, and disposal of synthetic textiles potentially release a significant amount of microfibers into the environment. Studies performed on municipal wastewater treatment plants (WWTPs) effluent reported a higher presence of microfibers due to the mix of domestic laundry effluent through sewage. As municipal WWTPs receive influents from households and industries, it serves as a sink for the microfibers. However, research on textile industry WWTPs that primarily treat the textile fabric processing wastewater was not explored with the concern of microfibers. Hence, the review aims to analyze the existing literature and enlighten the impact of WWTPs on microplastic emission into the environment by specifically addressing textile industry WWTPs. The results of the review confirmed that even after 95-99% removal, municipal WWTPs can emit around 160 million microplastics per day into the environment. Microfiber was the dominant shape identified by the review. The average microfiber contamination in the WWTP sludge was estimated as 200 microfibers per gram of sludge. As far as the industry-specific effluents are analyzed, textile wet processing industries effluents contained > 1000 times higher microfibers than municipal WWTP. Despite few existing studies on textile industry effluent, the review demonstrates that, so far, no studies were performed on the sludge obtained from WWTPs that handle textile industry effluents alone. Review results pointed out that more attention should be needed to the textile wastewater research which is addressing the textile wet processing industry WWTPs. Moreover, the sludge released from these WWTPs should be considered as an important source of microfiber as they contain more quantity of microfibers than the effluent, and also, their routes to the environment are huge and easy.

Assessment of microplastics in Irish river sediment

Microplastics (MPs) are environmental pollutants of growing concern, and awareness of MPs pollution in marine and freshwater environments has increased in recent years. However, knowledge of MPs contamination in riverine sediments in Ireland is limited. To address this, we collected and analysed sediment samples from 16 selected sites along the River Barrow. Microplastics were extracted through a density separation method, after which their size, colour, and shape were analysed under a stereo microscope (Optica SZM-2). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to identify polymer types. A total of 690 MPs were recovered from the 16 sites, with fibres as the dominant MP type. The highest concentration of MPs was 155 MP fibres kg-1 wet sediment found in samples collected from Graiguenamanagh, Co. Kilkenny (GK). The majority of the recovered MPs were polyethylene (PE), polypropylene (PP), nylon, and cellulose acetate (CA) fibres. Overall, this study highlighted the presence of MPs in Irish river sediments and provided a baseline for future studies on MPs pollution. Further research is needed to better understand sources, distribution, and effects of MPs in freshwater ecosystems.

Responses of nitrogen removal under microplastics versus nanoplastics stress in SBR: Toxicity, microbial community and functional genes

Microplastics (MPs) and nanoplastics (NPs), as emerging pollutants, are frequently detected in wastewater treatment plants. However, studies comparing the effects of MPs versus NPs on nitrogen removal by activated sludge are rarely reported. Here, the responses of nitrogen removal performance, microbial community and functional genes to MPs and NPs in sequencing batch reactors were investigated. Results revealed that MPs (10 and 1000 μg/L) had no effects on nitrogen removal. While upon exposure to NPs, although low concentration (10 μg/L) of NPs showed no remarkable influence on nitrogen removal, high level (1000 μg/L) of NPs decreased NH₄⁺-N removal efficiency by 24.48% and caused accumulation of NO₃^--N and NO₂^--N. These inhibitory probably due to the acute toxicity of NPs to activated sludge, which was reflected by the increasing reactive oxygen species generation and lactate dehydrogenase release. The toxic effects of NPs further declined the relative abundance of nitrifiers (e.g., Nitrospira) and denitrifiers (e.g., Dechloromonas). These negative effects, accompanied by a decrease in abundance of amoA and nxrA genes related to nitrification (30.01% and 65.24% of control) and narG, nirK and nirS genes associated with denitrification (78.59%, 61.39%, and 86.17% of control), directly illustrated the attenuate phenomenon observed in nitrogen removal.

Effects of Polyester Fibers and Car Tire Particles on Freshwater Invertebrates

Microplastic ingestion has been shown for various organisms, but knowledge of the potential adverse effects on freshwater invertebrates remains limited. We assessed the ingestion capacity and the associated effects of polyester fibers (26-5761 µm) and car tire particles (25-75 µm) on freshwater invertebrates under acute and chronic exposure conditions. A range of microplastic concentrations was tested on Daphnia magna, Hyalella azteca, Asellus aquaticus, and Lumbriculus variegatus using water only (up to 0.15 g/L) or spiked sediment (up to 2 g/kg dry wt), depending on the habitat of the species. Daphnia magna did not ingest any fibers, but low levels of fibers were ingested by all tested benthic invertebrate species. Car tire particle ingestion rose with increasing exposure concentration for all tested invertebrates and was highest in D. magna and L. variegatus. In most cases, no statistically significant effects on mobility, survival, or reproductive output were observed after acute and chronic exposure at the tested concentrations. However, fibers affected the reproduction and survival of D. magna (no-observed-effect concentration [NOEC]: 0.15 mg/L) due to entanglement and limited mobility under chronic conditions. Car tire particles affected the reproduction (NOEC: 1.5 mg/L) and survival (NOEC: 0.15 mg/L) of D. magna after chronic exposure at concentrations in the same order of magnitude as modeled river water concentrations, suggesting that refined exposure and effect studies should be performed with these microplastics. Our results confirm that microplastic ingestion by freshwater invertebrates depends on particle shape and size and that ingestion quantity depends on the exposure pathway and the feeding strategy of the test organism. Environ Toxicol Chem 2022;41:1555-1567. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Emerging investigator series: microplastic sources, fate, toxicity, detection, and interactions with micropollutants in aquatic ecosystems - a review of reviews

Hundreds of review studies have been published focusing on microplastics (MPs) and their environmental impacts. With the microbiota colonization of MPs being firmly established, MPs became an important carrier for contaminants to step inside the food web all the way up to humans. Thus, the continuous feed of MPs into the ecosystem has sparked a multitude of scientific concerns about their toxicity, characterization, and interactions with microorganisms and other contaminants. The reports of common subthemes have agreed about many findings and research gaps but also showed contradictions about others. To unravel these equivocal conflicts, we herein compile all the major findings and analyze the paramount discrepancies among these review papers. Furthermore, we systematically reviewed all the highlights, research gaps, concerns, and future needs. The covered focus areas of MPs' literature include the sources, occurrence, fate, existence, and removal in wastewater treatment plants (WWTPs), toxicity, interaction with microbiota, sampling, characterization, data quality, and interaction with other co-contaminants. This study reveals that many mechanisms of MPs' behavior in aquatic environments like degradation and interaction with microbiota are yet to be comprehended. Furthermore, we emphasize the critical need to standardize methods and parameters for MP characterization to improve the comparability and reproducibility of the incoming research.

Long-Term Occurrence and Fate of Microplastics in WWTPs: A Case Study in Southwest Europe

Microplastic (MP) water pollution is a major problem that the world is currently facing, and wastewater treatment plants (WWTPs) represent one of the main alternatives to reduce the MP release to the environment. Several studies have analysed punctual samples taken throughout the wastewater treatment line. However, there are few long-term studies on the evolution of MPs over time in WWTPs. This work analyses the performance of a WWTP sited in Southwest Europe in relation with annual occurrence and fate of MPs. Samples were monthly taken at different points of the facility (influent, secondary effluent, final effluent, and sludge) and MPs were quantified and characterised by means of stereomicroscopy and FTIR spectrophotometry. The majority of MPs found in wastewater and sludge samples were fragments and fibres. Regarding to the chemical composition, in the water samples, polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP) stood out, whereas, in the sludge samples, the main polymers were PET, polyamide (PA) and polystyrene (PS). The MPs more easily removed during the wastewater treatment processes were those with sizes greater than 500 µm. Results showed that the MPs removal was very high during all the period analysed with removal efficiencies between 89% and 95%, so no great variations were found between months. MP concentrations in dry sludge samples ranged between 12 and 39 MPs/g, which represented around 79% of the total MPs removed during the wastewater treatment processes. It is noticeable that a trend between temperature and MPs entrapped in sewage sludge was observed, i.e., higher temperatures entailed higher percentage of retention.

A critical review of microplastics in the soil-plant system: Distribution, uptake, phytotoxicity and prevention

Microplastics (MPs) are creating an emerging threat on the soil ecosystems and are of great global concern. However, the distribution in soil-plant system, as well as the phytotoxicity and impact mechanisms of MPs remain largely unexplored so far. This study introduced the diverse sources of MPs and showed the significant spatial variation in the global geographic distribution of MPs contamination based on data collected from 116 studies (1003 sampling sites). We systematically discussed MPs phytotoxicity, such as plant uptake and migration to stems and leaves, delaying seed germination, impeding plant growth, inhibiting photosynthesis, interfering with nutrient metabolism, causing oxidative damage, and producing genotoxicity. We further highlighted the alterations of soil structure and function by MPs, as well as their self and load toxicity, as potential mechanisms that threaten plants. Finally, this paper provided several preventive strategies to mitigate soil MPs pollution and presented research gaps in the biogeochemical behavior of MPs in soil-plant systems. Meanwhile, we recommended that methods for the quantitative detection of MPs accumulated in plant tissues should be explored and established as soon as possible. This review will improve the understanding of the environmental behavior of MPs in soil-plant systems and provide a theoretical reference to better assess the ecological risk of MPs.

Microplastics as an aquatic pollutant affect gut microbiota within aquatic animals

The adverse impact of microplastics (MPs) on gut microbiota within aquatic animals depends on the overall effect of chemicals and biofilm of MPs. Thus, it is ideal to fully understand the influences that arise from each or even all of these characteristics, which should give us a whole picture of consequences that are brought by MPs. Harmful effects of MPs on gut microbiota within aquatic organisms start from the ingestion of MPs by aquatic organisms. According to this, the present review will discuss the ingestion of MPs and its following results on gut microbial communities within aquatic animals, in which chemical components, such as plastic polymers, heavy metals and POPs, and the biofilm of MPs would be involved. This review firstly analyzed the impacts of MPs on aquatic organisms in detail about its chemical components and biofilm based on previous relevant studies. At last, the significance of field studies, functional studies and complex dynamics of gut microbial ecology in the future research of MPs affecting gut microbiota is discussed.

Fate of microplastics in agricultural soils amended with sewage sludge: Is surface water runoff a relevant environmental pathway?

Sewage sludge used as agricultural fertilizer has been identified as an important source of microplastics (MPs) to the environment. However, the fate of MPs added to agricultural soils is largely unknown. This study investigated the fate of MPs in agricultural soils amended with sewage sludge and the role of surface water runoff as a mechanism driving their transfer to aquatic ecosystems. This was assessed using three experimental plots located in a semi-arid area of Central Spain, which were planted with barley. The experimental plots received the following treatments: (1) control or no sludge application; (2) historical sludge application, five years prior to the experiment; and (3) sludge application at the beginning of the experiment. MPs were analyzed in surface water runoff and in different soil layers to investigate transport and infiltration for one year. The sewage sludge used in our experiment contained 5972-7771 MPs/kg dw. Based on this, we estimated that about 16,000 MPs were added to the agricultural plot amended with sludge. As expected, the sludge application significantly increased the MP concentration in soils. The control plot contained low MP concentrations (31-120 MPs kg^-1 dw), potentially originating from atmospheric deposition. The plot treated five years prior to the experiment contained 226-412 and 177-235 MPs kg^-1 dw at the start and end of the experiment, respectively; while the recently treated plot contained 182-231 and 138-288 MPs kg^-1 dw. Our study shows that MP concentrations remain relatively constant in agricultural soils and that the MP infiltration capacity is very low. Surface water runoff had a negligible influence on the export of MPs from agricultural soils, mobilizing only 0.2-0.4% of the MPs added with sludge. We conclude that, in semi-arid regions, agricultural soils can be considered as long-term accumulators of MPs.

Interactions between microplastics and unit processes of wastewater treatment plants: a critical review

Microplastics are classified as emerging pollutants of the aquatic environment, necessitating a comprehensive understanding of their properties for successful management and treatment. Wastewater treatment plants (WWTPs) serve as point sources of microplastic pollution of the aquatic and terrestrial (eco)systems. The first part of this review explores the basic definitions of microplastics, sources, types, physical and chemical methods of identifying and characterizing microplastics in WWTPs. The next part of the review details the occurrence of microplastics in various unit processes of WWTPs and sewage sludge. Followed by this, various methods for removing microplastics from wastewater are presented. Finally, the research gaps in this area were identified, and suggestions for future perspectives were provided.

Comparative bibliometric trends of microplastics and perfluoroalkyl and polyfluoroalkyl substances: how these hot environmental remediation research topics developed over time

Bibliometrics point to the hottest areas of science and policy working to reverse the environmental impacts of PFAS and microplastics.

Effects of microplastics accumulation on performance of membrane bioreactor for wastewater treatment

The effective interception of membrane leads to the accumulation of microplastics (MPs) in membrane bioreactor (MBR) process for long-term operation. However, the influence of MPs accumulation on the performance of MBR hasn't been well understood. In this study, the accumulation of polypropylene microplastics (PP-MPs) in two MBRs run for 3 yr with or without discharging sludge was simulated by operating the lab-scale MBRs for 84 days. The variations of pollutant removal, membrane fouling, composition of soluble microbial product (SMP) and extracellular polymeric substance (EPS), and microbial community of MBRs were systematically investigated. The results show that the removal efficiency of COD and NH₄⁺-N was not depressed by PP-MPs accumulation. However, the presence of PP-MPs in the range of 0.14-0.30 g/L could inhibit the growth of microorganisms, enhance the secretion of SMP and EPS, and reduce the microbial richness and diversity. In the contrary, the high concentration of PP-MPs (2.34-5.00 g/L) exhibited the opposite effects and mitigated membrane fouling, suggesting the important role of MPs concentration. It was also found that the exposure to high concentration of PP-MPs enhanced relative abundance of Clostridia, and inhibited the growth of Proteobacteria. The findings of this study provide a foresight to understand the effects of MPs accumulation on the performance of MBRs.

Emission, Transport, and Deposition of visible Plastics in an Estuary and the Baltic Sea-a Monitoring and Modeling Approach

was to assess whether a comprehensive approach linking existing knowledge with monitoring and modeling can provide an improved insight into coastal and marine plastics pollution. We focused on large micro- and mesoplastic (1-25 mm) and selected macroplastic items. Emission calculations, samplings in the Warnow river and estuary (water body and bottom sediments) and a flood accumulation zone monitoring served as basis for model simulations on transport and behavior in the entire Baltic Sea. Considered were the most important pathways, sewage overflow and stormwater. The coastline monitoring together with calculations allowed estimating plastics emissions for Rostock city and the Warnow catchment. Average concentrations at the Warnow river mouth were 0.016 particles/m³ and in the estuary 0.14 particles/m³ (300 µm net). The estuary and nearby Baltic Sea beaches were hot-spots for plastic accumulation with 6-31 particles/m². With increasing distance from the estuary, the concentrations dropped to 0.3 particles/m². This spatial pattern, the plastic pollution gradients and the observed annual accumulation values were consistent with the model results. Indicator items for sewer overflow and stormwater emissions exist, but were only found at low numbers in the environment. The considered visible plastics alone can hardly serve as indicator for microplastic pollution (<1 mm). The use of up-scaled emission data as input for Baltic Sea model simulations provided information on large scale emission, transport and deposition patterns of visible plastics. The results underline the importance of plastic retention in rivers and estuaries.

Understanding the fate of nano-plastics in wastewater treatment plants and their removal using membrane processes

Nanoplastics (NPs) have become a major environmental issue due to their adverse effect on the water environment. Wastewater treatment plant (WWTP) is considered as one of the main sources for breaking down of larger-sized plastic debris and microplastics (MPs) into NPs. This study aims to provide a comprehensive understanding of NPs generation in the WWTPs, their physiochemical characteristics and interaction with the WWTPs. It is found that cracking is the major mechanism of plastics fragmentation in the WWTPs. This review also discusses the current membrane process used for NPs removal. It is found that conventional membrane processes are ineffective as they are not designed for NPs removal and fouling is a major obstacle for its application. Therefore, this study concludes by providing an outlook of developing a bio-nanofiltration process that can be used as a tertiary treatment for removing NPs and other components present in water. Such a process can produce NPs-free water for non-potable use or safe discharge into open waterways.

Combining citizen and conventional science for microplastics monitoring in the White Sea basin (Russian Arctic)

The study presents the results of the field expedition in the Russian Arctic held by a group of NGO members, scientists and volunteers in summer-autumn 2020 in the Arkhangelsk Region (Russia). The survey showed microplastics presence in 7 out of 13 remote and sparsely inhabited locations in lakes, rivers and coastal areas of the White Sea basin, with microplastic particle average concentration 1.14 part/m³, that is in agreement with other recent regional studies. Mostly PE, PET and PVC were found. A simple, cheap and easy-to-use microplastics monitoring protocol was developed and tested to be used by volunteers in remote Arctic communities. Video-lectures and tutorials are available online in an open-aсcess mode. 200 volunteers from polar communities are trained in microplastic sampling and litter separation, learning about microplastic pollution, including local residents, schoolchildren and students.

Fourier transform infrared (FTIR) analysis identifies microplastics in stranded common dolphins (Delphinus delphis) from New Zealand waters

Here we provide a first assessment of microplastics (MPs) in stomach contents of 15 common dolphins (Delphinus delphis) from both single and mass stranding events along the New Zealand coast between 2019 and 2020. MPs were observed in all examined individuals, with an average of 7.8 pieces per stomach. Most MPs were fragments (77%, n = 90) as opposed to fibres (23%, n = 27), with translucent/clear (46%) the most prevalent colour. Fourier transform infrared (FTIR) spectroscopy revealed polyethylene terephthalate (65%) as the most predominant polymer in fibres, whereas polypropylene (31%) and acrylonitrile butadiene styrene (20%) were more frequently recorded as fragments. Mean fragment and fibre size was 584 μm and 1567 μm, respectively. No correlation between total number of MPs and biological parameters (total body length, age, sexual maturity, axillary girth, or blubber thickness) was observed, with similar levels of MPs observed between each of the mass stranding events. Considering MPs are being increasingly linked to a wide range of deleterious effects across taxa, these findings in a typically pelagic marine sentinel species warrants further investigation.

Evidence for Microplastics Contamination of the Remote Tributary of the Yenisei River, Siberia—The Pilot Study Results

This study is a pioneering attempt to count microplastics (MPs) in the Yenisei River system to clarify the role of Siberian Rivers in the transport of MPs to the Arctic Ocean. The average MPs content in the surface water of the Yenisei large tributary, the Nizhnyaya Tunguska River, varied from 1.20 ± 0.70 to 4.53 ± 2.04 items/m3, tending to increase along the watercourse (p < 0.05). Concentrations of MPs in bottom sediments of the two rivers were 235 ± 83.0 to 543 ± 94.1 with no tendency of downstream increasing. Linear association (r = 0.952) between average organic matter content and average counts of MPs in bottom sediments occurred. Presumably MPs originated from the daily activities of the in-situ population. Further spatial-temporal studies are needed to estimate the riverine MPs fluxes into the Eurasian Arctic seas.

Spatio-temporal distribution of microplastics in a Mediterranean river catchment: The importance of wastewater as an environmental pathway

Microplastics (MPs) are considered to be ubiquitous contaminants in freshwater ecosystems, yet their sources and pathways at the river catchment scale need to be better determined. This study assessed MP (55-5000 µm) pollution in a Mediterranean river catchment (central Spain) and aimed to identify the importance of wastewater as an environmental pathway. We sampled treated and untreated wastewaters, and raw and digested sludge from five WWTPs during two seasons. River water and sediments were sampled at three locations with different anthropogenic influences during three seasons. On average, 93% (47-99%) of MPs were retained by WWTPs. Concentrations in river water and sediment ranged between 1 and 227 MPs/m³ and 0-2630 MPs/kg dw, respectively. Concentrations strongly depended upon land-use, with pollution levels increasing significantly downstream of urban and industrial areas. Seasonality influenced the observed MP concentrations strongly. During high flow periods, higher water but lower sediment concentrations were observed compared to low flow periods. We estimate that 1 × 10¹⁰ MPs are discharged into the catchment via treated and untreated wastewater annually, which constitutes up to 50% of the total MP catchment discharge. Thus, we conclude that the wastewater system represents a major environmental pathway for MPs into Mediterranean rivers with low dilution capacity.

Assessment of microplastics in discharged treated wastewater and the utility of Chrysaora pentastoma medusae as bioindicators of microplastics

Microplastics are ubiquitous pollutants in aquatic environments globally. Wastewater treatment plants are considered to be a major source of microplastics and jellyfish have been proposed as potential bioindicators of microplastic pollution. We tested whether treated wastewater influenced the concentration and/or composition of microplastics in the receiving water by comparing the concentration and composition of microplastics in seawater collected in the wastewater plume and at sites distant from treated wastewater releases in the Gold Coast Broadwater, Australia, and at sites within the nearby Tweed River estuaries, which receives >10 times less wastewater discharge. In addition, tiger sea nettle Chrysaora cf. pentostoma medusae were collected to determine whether more microplastics occurred in the guts of the medusae nearby diffusers and whether the microplastics ingested by medusae were representative of those present in the water column. The concentration and composition of microplastics at the wastewater release sites did not significantly differ from sites that were distant from them. Eighty three percent of medusae contained microplastics in their guts and the composition of the ingested microplastics differed significantly from that in the surrounding water. We concluded that discharged treated wastewater had no detectable effect on levels or composition of microplastics in the receiving water and that C. pentostoma are unsuitable bioindicators because the microplastics they ingested did not represent those available in their environment.

Sewage sludge as a source of microplastics in the environment: A review of occurrence and fate during sludge treatment

Modern wastewater treatment plants (WWTPs) effectively remove microplastics (MPs) from wastewater and unsurprisingly concentrate them in sludge. Hence through its beneficial use and disposal, sludge causes secondary release pathways of an estimated average amount of 10⁶ to 10¹⁴ wastewater-based MPs to various environmental compartments yearly. Despite these numbers, studies investigating sludge are scarce. Currently, majority of the studies in the field focus on identifying the magnitude of the problem, whereas research investigating the fate and effects of MPs during sludge treatment are very rare. This review aims to bring together and critically evaluate the limited studies conducted about MPs in the sludge treatment line and bring out the key gaps and research needs in the area. Studies conducted so far indicate that depending on the type, size, and amount of MPs, their effects during anaerobic digestion differ, with some studies demonstrating serious negative impact on biogas production. Possible effect mechanisms are also suggested such as formation of reactive oxygen species (ROS) and leaching of toxic chemicals. Moreover, a potential for sludge treatment processes (thickening, dewatering, drying, stabilization, etc.) to change the characteristics and the number of MPs, which may increase surface area available for adsorption and desorption of pollutants, was observed. Review uncovers that, in the broad universe of MPs, some highly abundant ones in sludge such as polypropylene, polyurethane, polycarbonate, and acrylic are not yet investigated in sludge treatment. Future research should focus not only to investigate the fate/effects but to fully understand the mechanisms behind these, which is missing in many studies reviewed. Besides, new studies show that effect of MPs start from the floc formation stage during biological treatment, which in fact determine the final sludge behavior in thickening and dewatering. Therefore, holistic approaches starting from wastewater till sludge exits WWTP seem necessary. Substantiating from polymer chemistry and response of plastics to stress conditions, review suggests possibilities of deterioration during sludge treatment processes. It becomes evident that some totally uninvestigated aspects such as disintegration conducted before stabilization, can change the fate of MPs during sludge treatment and may bring new perspectives to the solution of the problem.

The Py - GC-TOF-MS analysis and characterization of microplastics (MPs) in a wastewater treatment plant in Gauteng Province, South Africa

Wastewater treatment plants (WWTPs) in South Africa, like is the case for most WWTPs around the globe albeit capable of removing substantial quantities of microplastics (MPs) and in fact, the treatments become ineffective for those plastic particles less than 100 µm. As a consequence, the receiving water bodies in which the final effluent is discharged becomes highly polluted. The present research is devoted to the analysis of the pervasive MPs in wastewaters of the treatment plant located in the Gauteng Province, South Africa using Pyrolysis - GC-TOF-MS. Based on the results, there were 23 pyrolyzate products with contributions from PVC, PA, PET and PE with abundances of 47.8%, 13.1%, 17.4% and 4.3% respectively. The remaining 17.4% could be attributed as additives in MPs. The SEM images illustrated that the MPs appeared to be inter - wined, fibrous of different thicknesses and lengths. The highly weathered MPs exhibited the rough surface which was noticeably damaged with peeled off layers presumably because of photo-oxidation during the aging process. The vibrational modes of FTIR revealed the presence of the various functional groups in the corresponding polymers of MPs. The thermal studies confirmed the presence of calcium, aluminum and silicon as residues of catalysts or flame retardants or UV stabilizers in MPs or as adsorbates resulting from the surface adsorption from the surroundings. The Py-GC-TOF-MS confirmed the identity of the various fragments related to the MPs monomers.

Plastic pollution during COVID-19: Plastic waste directives and its long-term impact on the environment

Majority of the million tons of plastic produced each year is being disposed after single-use. Plastic bottle, bags, food containers, gloves, and cup that end up in landfills and environment could linger for hundreds to thousands of years. Moreover, COVID-19 pandemic caused by the novel coronavirus (SARS-CoV-2), will also exacerbate the global plastic pollution as the use of personal protective equipment (PPE i.e., gloves, masks) became mandatory to prevent the spread of the virus. Plastic eventually breaking down in micro & nanoscopic bits due to physical or chemical or biological actions in the environment, can enter animal and human food web. So, plastic management programs need to be more robust with a focus on the prevention of the micro and nanoplastics entrance into the environment and food web. In the present pandemic situation, it is even more necessary to know about how much plastic waste is being generated and how different countries are coping up with their plastic waste management. In this review, we have elucidated how global plastic production rise during COVID-19 and how it would contribute to short and long-term impacts on the environment. Plastic pollution during the pandemic will increase the GHS emissions in the incineration facilities. Improper disposal of plastics into the oceans and lands would endanger the marine species and subsequently human lives. We have also assessed how the increased plastic pollution will aggravate the micro and nanoscale plastic problem, which have now become an emerging concern. This review will be helpful for people to understand the plastic usage and its subsequent consequences in the environment in a pandemic like COVID-19.

Impacts of baseflow and flooding on microplastic pollution in an effluent-dependent arid land river in the USA

Effluent discharge from wastewater treatment plants can be a substantial source of microplastics in receiving water bodies including rivers. Despite growing concern about microplastic pollution in freshwater habitats, the literature has not yet addressed effluent-dependent rivers, which derive 100% of their baseflow from effluent. The objective of this study was to document and explore trends in microplastic pollution within the effluent-dependent lower Santa Cruz River near Tucson, Arizona (USA). We examined microplastic concentrations in the water column and benthic sediment and microplastic consumption by mosquitofish (Gambusia affinis) at 10 sites along a ~40 km stretch of the lower Santa Cruz River across two time periods: baseflow (effluent only) and post-flood (effluent immediately following urban runoff). In total, across both sampling periods, we detected microplastics in 95% of water column samples, 99% of sediment samples, and 6% of mosquitofish stomachs. Flow status (baseflow vs post-flood) was the only significant predictor of microplastic presence and concentrations in our models. Microplastic fragment concentrations in the water column were higher post-flood, microplastic fiber concentrations in benthic sediment were lower post-flood, and mosquitofish were more likely to have consumed microplastics post-flood than during baseflow. The additional microplastics detected after flooding was likely due to a combination of allochthonous material entering the channel via runoff and bed scour that exhumed microplastics previously buried in the riverbed. Effluent-dependent urban streams are becoming increasingly common; more work is needed to identify microplastic pollution baselines and trends in effluent rivers worldwide.

Microplastics in polar regions: An early warning to the world's pristine ecosystem

The menace of plastic which is polluting the ocean has emerged as a global problem. It is well-known to everyone that the ultimate end for most of the plastic debris is the ocean. The distribution of plastic rubbish in the oceans is strongly influenced by hydrodynamic properties of water. The continuous break down of plastic objects, as a consequence of thermal, chemical and biological processes along with various environmental factors, results into microplastics (MPs). The microplastics are those particles which are deriving pallets of plastic, having length of less than 5 mm or 0.2 in. Nowadays microplastics are everywhere in the waters all around the world. The high dispersion pattern of oceanic currents takes away microplastics in the entire ocean even to remote areas, like the Polar Regions. Microplastics are difficult to remove from the ocean and the ingestion of these particles by several consumers of different trophic levels like benthos, birds, and fishes is a threat to the diverse food webs and ecosystems. Different scientific investigations have ascertained that a significant concentration of MPs are present in various marine ecosystems globally including the Polar region (both Arctic and Antarctic), and in the upcoming future, the condition is expected to get worse. The objective of this review is to establish a baseline evidence for the availability of microplastics in the polar region. For this reason, the state of the art of knowledge on microplastics in Polar Regions was studied.

Microplastic and Organic Fibres in Feeding, Growth and Mortality of Gammarus pulex

Microplastic fibres (MPFs) are a major source of microplastic pollution, most are released during domestic washing of synthetic clothing. Organic microfibres (OMF) are also released into the environment by the same means, with cotton and wool being the most common in the UK. There is little empirical evidence to demonstrate that plastic fibres are more harmful than organic fibres if ingested by freshwater animals such as Gammarus pulex. Using our method of feeding Gammarus MPFs embedded in algal wafers, we compared the ingestion, feeding behaviour and growth of Gammarus exposed to 70 µm sheep wool, 20 µm cotton, 30 µm acrylic wool, and 50 µm or 100 µm human hair, and 30 µm cat hair at a concentration of 3% fibre by mass. Gammarus would not ingest wafers containing human hair, or sheep wool fibres. Given the choice between control wafers and those contaminated with MPF, cat hair or cotton, Gammarus spent less time feeding on MPF but there was no difference in the time spent feeding on OMFs compared to the control. Given a choice between contaminated wafers, Gammarus preferred the OMF to the MPF. There were no significant differences in growth or mortality among any of the treatments. These results conclude that MPFs are less likely to be ingested by Gammarus if alternative food is available and are not more harmful than OMFs.

A complete mass balance for plastics in a wastewater treatment plant - Macroplastics contributes more than microplastics

A complete plastic particle mass balance was established at Sweden's second-largest wastewater treatment plant. It comprised material collected at its two bar screens, a 20 mm and a 2 mm one, in the influent water after the 20 mm screen, the effluent water, and the digested sludge. Macro- and microplastics above 500 µm were analysed individually applying ATR-FTIR, while microplastics of 10-500 µm were analysed by µFTIR imaging with automated particle recognition. Masses of plastics >500 µm were determined by weighting, while the mass of the smaller microplastics was estimated from the imaging. The total plastic load on the plant was 202.2 kg d^-1, of which the two screens retained 73%. The remaining plastic mass was found in the sludge (13.6%) and the effluent (0.4%). The missing 12.7% could be caused by sampling and measuring uncertainties and potentially also fragmentation below the size detection limit of the analytical approach, or by degradation. The bar screens furthermore retained plastics smaller than the screen size, indicating that this material should be taken into account also when solely looking at smaller particles. The overall treatment efficiency of the plant was high: 99.6% considering both macro- and microplastics, and 98.8% considering only microplastics <500 µm.

Occurrence, effect, and fate of residual microplastics in anaerobic digestion of waste activated sludge: A state-of-the-art review

The plastic products have large consumption over last decades, resulting in a serious microplastics (MPs) pollution. Specially, the main removal way of MPs from wastewater is to transfer MPs from liquid to solid phase, leading to its enrichment in waste activated sludge (WAS). Anaerobic digestion has been served as the most potential technique to achieve both resource recovery and sludge reduction, herein this review provides current information on occurrence, effect, and fate of MPs in anaerobic digestion of WAS. The effects of MPs on WAS anaerobic digestion are greatly related to forms, particles sizes, contents, compositions and leachates of MPs. Also, the presence of MPs not only can change the effects of other pollutants on anaerobic digestion of WAS, but also can affect the fates of them. Besides, the future perspectives focused on the fate, effect and final removal of MPs during WAS anaerobic digestion process are outlined.

From the ocean to jellies forth and back? Microplastics along the commercial life cycle of red algae

Red algae are increasingly exploited for direct consumption and for production of gelling agents like agar and carrageenan, widely employed in food and personal care products. In this article we identify knowledge gaps about microplastics in the whole commercial life cycle of gelling red algae, from their marine production to the final wastewater treatment. Recommendations for new research include studies of microplastics deposition on red algae at sea, during the industrial process of production of gelling agents, and indeed about improvements of microplastics retention in wastewater treatment plants.

Surface-functionalised materials for microplastic removal

Microplastic (MP) pollution is a matter of great concern attracting increasing attention due to its adverse effects on the environment. Different technologies and methodologies have been developed to remove these pollutants. Herein, we focus on a promising environmental solution that involves surface modification to change the wettability properties of MPs or solid materials by conferring superhydrophobicity and superoleophilicity to increase the selectivity for MP separation. Both processes can be used to selectively separate MPs because of the changes in the wettable properties of the MP or by changing the oil used in the case of superhydrophobic surfaces. We show two distinct methods based on changing the wettability properties of surfaces that could lead to innovative and environmental applications. We also discuss some of the challenges that need to be overcome.

Solid waste: An overlooked source of microplastics to the environment

Microplastics pollution is one of the most pressing environmental problems of the 21st century. While microplastics are pervasive throughout various environmental compartments, research to date has primarily focused on marine systems. Land-based microplastics sources (e.g., solid waste) have received comparatively little attention, although they account for the main flow of microplastics into aquatic environments. Solid waste microplastics sources primarily include landfill refuse, sludge, and food waste. Microplastics in these waste streams can be associated with various micropollutants that can have deleterious impacts on ecosystem health as they enter the food chain. Thus, understanding the occurrence, fate, and degradation pathways of solid waste microplastics is essential to develop comprehensive control and mitigation strategies. This study critically reviewed these key aspects of microplastics in municipal solid waste landfill refuse, sewage sludge, and food waste, and identified the interconnections of these components in the proliferation of microplastics to the environment. Additionally, microplastics related laws and regulations and their relevance to solid waste microplastics mitigation are discussed.

Plastisphere enrich antibiotic resistance genes and potential pathogenic bacteria in sewage with pharmaceuticals

Microplastics (MPs) and pharmaceuticals are common emerging pollutants in sewage, and their coexistence may have more negative effects on the environments. This study chose tetracycline (TC), ampicillin (AMP) and triclosan (TCS) to investigate the responses of antibiotic resistance genes (ARGs) and microbial communities on different MPs (polyvinyl chloride (PVC), polyethylene (PE)) biofilms (plastisphere). The adsorption capacity of three pharmaceuticals on PVC and PE decreased in the order of AMP > TC > TCS. PE was more conducive to microbial attachment than PVC. MPs led to the increase of the total copies of ARGs and mobile genetic elements (MGEs) in the sewage. Importantly, multidrug ARGs and MGEs were enriched on plastisphere. Furthermore, the co-occurrence of TC and MPs led to higher risks of spreading ARGs and MGEs. In addition, potential pathogenic bacteria Legionella, Mycobacterium, Neisseria and Arcobacter were more abundant on plastisphere than those in sewage, and these bacteria might be the hosts for ARGs and MGEs. This study showed that plastisphere could be repositories of ARGs and MGEs in sewage and accumulated potential pathogenic bacteria.

Label-free identification and differentiation of different microplastics using phasor analysis of fluorescence lifetime imaging microscopy (FLIM)-generated data

As plastic pollution is becoming an increasing worldwide problem, a variety of different techniques for the detection and in-depth characterization of plastics, including spectroscopy and chromatography methods, were introduced to the public. Recently we presented fluorescence lifetime imaging microscopy (FLIM) a new approach for the identification and characterization of microplastics using their fluorescence lifetime (τ) for differentiation. A very powerful extension of the recently established FLIM could be phasor analysis, which allows data representation in an interactive 2D graphical phasor plot thereby enabling a global view of the fluorescence decay in each pixel of the measured image. Microplastic particles generated from six different types of plastics were subjected to excitation wavelengths of 440 nm, upon which specific fluorescence lifetimes as well as the photon yield were determined using FLIM and phasor analysis. We could show that phasor analysis for FLIM with a laser pulse repetition frequency of 40 MHz was able to generate specific locations in the phasor plot for the plastics for fast differentiation, e.g. resulting in well-defined phasor plot positions for ABS at 3.019 ns, PPE at 6.239 ns, PET bottle from Germany at 2.703 ns and PET bottle from USA at 2.711 ns. Phasor analysis for FLIM proves to be a fast, label-free, and sensitive method for the identification and differentiation of plastics also with the aid of visualization variation enabling techniques such as heat treatment of plastics.

Effect of microplastics in water and aquatic systems

Surging dismissal of plastics into water resources results in the splintered debris generating microscopic particles called microplastics. The reduced size of microplastic makes it easier for intake by aquatic organisms resulting in amassing of noxious wastes, thereby disturbing their physiological functions. Microplastics are abundantly available and exhibit high propensity for interrelating with the ecosystem thereby disrupting the biogenic flora and fauna. About 71% of the earth surface is occupied by oceans, which holds 97% of the earth's water. The remaining 3% is present as water in ponds, streams, glaciers, ice caps, and as water vapor in the atmosphere. Microplastics can accumulate harmful pollutants from the surroundings thereby acting as transport vectors; and simultaneously can leach out chemicals (additives). Plastics in marine undergo splintering and shriveling to form micro/nanoparticles owing to the mechanical and photochemical processes accelerated by waves and sunlight, respectively. Microplastics differ in color and density, considering the type of polymers, and are generally classified according to their origins, i.e., primary and secondary. About 54.5% of microplastics floating in the ocean are polyethylene, and 16.5% are polypropylene, and the rest includes polyvinyl chloride, polystyrene, polyester, and polyamides. Polyethylene and polypropylene due to its lower density in comparison with marine water floats and affect the oceanic surfaces while materials having higher density sink affecting seafloor. The effects of plastic debris in the water and aquatic systems from various literature and on how COVID-19 has become a reason for microplastic pollution are reviewed in this paper.

Evaluation of the available strategies to control the emission of microplastics into the aquatic environment

No effective strategy has been found so far to control the emission of microplastics. The purpose of this article is to review the available control strategies, as well as barriers to developing them. Based on the estimations in the available literature, decomposition of larger plastics, clothes washing and tire abrasion play an essential part in the total emission rate of microplastics into the ocean. Nonetheless, there is no corresponding information regarding the soil, and more information is needed to prioritize the emission sources of microplastics more preciously. Generally, there have been two approaches for the management of the microplastic issues, including the substitution of non-plastic materials for plastic ones in products such as personal care products, and microplastic removal from wastewater. The former is in its infancy and has commenced only in a few developed countries. Existing wastewater treatment plants (WWTPs) as the other approach can transfer a significant portion of the microplastics into the sludge. The result is that the final destination of these microplastics can be the soil. Since there is little information on how serious the impact of microplastics is on the soil as compared with water, the currently used WWTPs cannot be considered as a final remedy. Furthermore, there has been not been any specifically designed techniques to remove microplastics from wastewater efficiently and economically.

A robust and anticorrosion non-fluorinated superhydrophobic aluminium surface for microplastic removal

Solid particulate pollutants such as microplastics constitute a global environmental issue in the 21st century. Many studies are exploring ways of removing these particles from marine environments such as seas and oceans. Here, we present a superhydrophobic surface obtained by combining anodisation and the liquid-phase deposition of lauric acid. The superhydrophobic surface was examined by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) to elucidate its hierarchical structure and wetting state, while time-of-flight secondary ion mass spectrometry (TOF-SIMS) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) were applied to identify the chemical composition of the surface, which revealed that aluminium laurate decreased the surface free energy. As microplastics are usually found in saline water, it was important to study the anticorrosion properties of the surface. Polarisation curves of the anodised surface showed excellent anticorrosion properties in 3.5 wt% NaCl aqueous solution, which was enhanced by the superhydrophobic properties when the aluminium surface was anodised for 60 min. The functionalised surface was superhydrophobic (154°) and superoleophilic (0°). These wetting properties allowed the surface to remove microplastics from the NaCl aqueous solution with an efficiency higher than 99%. Thus, we present a novel application of a superhydrophobic and anticorrosive surface in the removal of microplastics. This has not been reported previously and provides a new scope for superwettable materials and their environmental applications.

Occurrence, fate and removal of microplastics as heavy metal vector in natural wastewater treatment wetland system

Microplastics pollution in aquatic ecosystems is of great concern; however, systemic investigations are still lacking in freshwater wetland systems used for wastewater treatment. The present study discusses such freshwater wetland system in Eastern India to understand its microplastics transport mechanism, heavy metals association and microplastics removal efficiency. Microplastics (63 µm - 5 mm) were heavily found in surface water and sediments of treatment ponds (7.87 to 20.39 items/L and 2124.84 to 6886.76 items/kg) and associated wastewater canals (30.46 to 137.72 items/L and 1108.78 to 34612.87 items/kg). A high content of toxic metals (As, Cd, Cr, Cu, Ni, Pb and Zn) were found on the microplastics with polyethylene terephthalate and polyethylene as major plastics types which were also found in fishes and macroinvertebrates of treatment ponds. Machine learning algorithm revealed a close association between microplastics content in fishes and surface water, indicating risk associated with floating microplastics to the aquatic biota. The study also revealed that microplastics were acting as heavy metals vector and potentially causing fish contamination. Surface water microplastics removing efficiency of the treatment ponds was estimated to be 53%. The study bespeaks about transport of microplastics through wastewater canals and their retention in treatment ponds emphasizing sustainability maintenance of natural wastewater treatment systems especially considering microplastics contamination to the aquatic biota of freshwater wetland systems.

Plastic in compost: Prevalence and potential input into agricultural and horticultural soils

To maintain and improve soil fertility, compost application is a widely recommended practice. We hypothesized that this practice is, however, also a main entry path for plastic into soil. Hence, we i) quantified the prevalence of plastic in eight composts from different composting plants and hardware stores to derive estimations about related plastic inputs into soil, and ii) characterized the properties of these plastic residues in regard to size and shape for further risk assessment. Plastic remains were analyzed via density separation (ZnCl₂) and light microscopy. Testing this method recovered 80 ± 29% of spiked plastic items. Applying this method revealed that all composts contained plastic particles in detectable amounts, with contents ranging from 12 ± 8 to 46 ± 8 particles kg^-1, corresponding to calculated plastic weights of 0.05 ± 0.08 to 1.36 ± 0.59 g kg^-1. Because of this high variability, an a-priori discrimination of plastic loads between compost types cannot be achieved. Upscaling these loads to common recommendations in composting practice, which range from 7 to 35 t compost ha^-1, suggest that compost application to agricultural fields goes along with plastic loads of 84,000 to 1,610,000 plastic items ha^-1 per year (a), respectively, amounting to 0.34 to 47.53 kg plastic ha^-1 a^-1. Large potential inputs should thus also occur for horticultural soils, where application rates of compost usually vary between 6.48 and 19.44 t ha^-1, therewith resulting in a minimum plastic contamination of 77,770 plastic items and 0.31 kg plastic ha^-1 a^-1, but a maximum amount of up to 894,240 plastic items and 26.4 kg plastic ha^-1 a^-1. We conclude that compost application must be considered as potential source of plastic for both agricultural and horticultural soils, and technical solutions are needed to minimize these contamination risks while continuing this practice as important option to secure soil health.

Potential human health risks due to environmental exposure to nano- and microplastics and knowledge gaps: A scoping review

Microplastics are an emerging global environmental contaminant that are affecting multiple spheres. Despite their ubiquity in all spheres of life and ecology, little is known about the health effects of microplastics exposure to humans. This scoping review explores the existing evidence on the potential human health effects of microplastics and subsequent knowledge gaps. An electronic search of published articles in PubMed, Scopus, EMBASE, Cochrane databases, and Google Scholar was conducted using a combination of subject headings and keywords relating to microplastics and human health effects. The initial search resulted in 17,043 published articles and grey literature documents. After a full review of published articles and their references, 129 publications were identified for further detailed review. These articles indicate that human exposure to microplastics can occur through ingestion, inhalation, and dermal contact due to their presence in food, water, air, and consumer products. Microplastics exposure can cause toxicity through oxidative stress, inflammatory lesions, and increased uptake or translocation. Several studies have demonstrated the potentiality of metabolic disturbances, neurotoxicity, and increased cancer risk in humans. Moreover, microplastics have been found to release their constituent compounds as well as those that are adsorbed onto their surface. Further research is needed to quantify the effects of microplastics on human health and their pathogenesis.

Micro-plastic pollution along the Bay of Bengal coastal stretch of Tamil Nadu, South India

In the present-day context, micro-plastic particles in a marine environment are increasingly ubiquitous and of considerable persistence. In line with the micro-plastic pollution, the present contribution is devoted to the investigation of micro-plastic particles (MPs) along the urban sandy beach called Marina, the renowned longest beach in India. Along the sea coast of about 5 km, the quantification of micro-plastic particles using optical microscope evidenced the granular, filamentous, filmy and tubular fragments in a total of 72 marine samples including those filtered in the marine water column (WAT; 24 samples), those found in wet sediment (WET; 24 samples) and those found in dry sand (DSS; 24 samples). The filamentous-typed plastics of 79%, 57% and 52%, respectively in WET, WAT and DSS dominated over the other granular and tubular types. The micro-plastic particles were in the range of 60-820 items per m³, 60-1620 items per kg and 20-1540 items per kg for WAT, WET and DSS, respectively. The standard deviation for the microplastics abundance were 193.1, 396.6 and 364.6 for WAT, WET and DSS respectively. Upon visual inspection, the micro particles were observed in eight different colors and most of the samples were found to contain two different fragment types. Apart from the optical microscopic examination, the micro-plastics particles were studied by scanning electron microscope (SEM) coupled with elemental analysis by energy dispersive spectroscopy (EDS). The energy spectral graphs displayed that the micro-filaments and micro-tubular particles contained polyesters and fluoro-polymers. The presence of few micro-filaments of polypropylene and polyethylene was also evidenced from their atomic percentage values of carbon of about 88% and 93%, respectively. The presence of fluoro-polymers and polyesters was also confirmed by Fourier Transform Infra-Red (FTIR). Excepting the fluoro-polymers, the micro-plastics particles contained elements arising from sea water (Na, Cl, S, Mg, Ca, K). Heavy metals such as Cu, Mn, Mo, Ru and Rh were observed in micro-tubular fragments. Fe and Ti elements were detected with the highest atomic percentage of 17.19 and 19.84 in micro-tubular fragments. All the observations and analyses give a photography of the nature and the spatial distribution of MPs along this Indian beach.

The difference of aggregation mechanism between microplastics and nanoplastics: Role of Brownian motion and structural layer force

In recent years, microplastics (MPs) and nanoplastics (NPs) have attracted worldwide attention because of the potential risks they pose to aquatic environments, but there are few studies on the difference of aggregation mechanism between MPs and NPs. In this study, 100 nm and 1 μm polystyrene plastics were selected as models to explore the aggregation mechanism of MPs/NPs under different aquatic environments. The influence of ion species and concentrations on the aggregation behaviors and kinetics were systematically investigated to predict the effects of water quality on the occurrence form of MPs and NPs based on DLVO theory and revised modified Smoluchowski theory. Results showed concentration, valence and hydrated ability of cations jointly affected the aggregation behavior of NPs. The critical coagulation concentration ratio of cations were consistent with Schulze-Hardy rules. But the different aggregation rate coefficients of same valent cations were ascribed to the structural layer force. Anion species played a role in the reaction-controlled regime by producing hydrogen ions to neutralize negative charges on NPs surfaces. Due to the strong Brownian motion and structural layer force, NPs would be stable in freshwater but preferentially aggregated when transport through brackish water, estuaries, eutrophication and high hardness areas and sea water, forming the accumulation hot spots of NPs in the sediment. While for MPs, physical process controlled the aggregation mechanism of them, leading to high stability in natural water and eventually transporting into marine environments. This study provided a theoretical foundation for assessing the transport, distribution, fate and ecological risks of MPs and NPs in realistic aquatic environments.

A review of the removal of microplastics in global wastewater treatment plants: Characteristics and mechanisms

Wastewater treatment plants (WWTPs) are considered to be the main sources of microplastic contaminants in the aquatic environment, and an in-depth understanding of the behavior of microplastics among the critical treatment technologies in WWTPs is urgently needed. In this paper, the characteristics and removal of microplastics in 38 WWTPs in 11 countries worldwide were reviewed. The abundance of microplastics in the influent, effluent, and sludge was compared. Then, based on existing data, the removal efficiency of microplastics in critical treatment technologies were compared by quantitative analysis. Particularly, detailed mechanisms of critical treatment technologies including primary settling treatment with flocculation, bioreactor system, advanced oxidation and membrane filtration were discussed. Thereafter, the abundance load and ecological hazard of the microplastics discharged from WWTPs into the aquatic and soil environments were summarized. The abundance of microplastics in the influent ranged from 0.28 particles L^-1 to 3.14 × 10⁴ particles L^-1, while that in the effluent ranged from 0.01 particles L^-1 to 2.97 × 10² particles L^-1. The microplastic abundance in the sludge within the range of 4.40 × 10³-2.40 × 10⁵ particles kg^-1. In addition, there are still 5.00 × 10⁵-1.39 × 10¹⁰ microplastic particles discharged into the aquatic environment each day Moreover, among the critical treatment technologies, the quantitative analysis revealed that filter-based treatment technologies exhibited the best microplastics removal efficiency. Fibers and microplastics with large particle sizes (0.5-5 mm) were easily separated by primary settling. Polyethene and small-particle size microplastics (<0.5 mm) were easily trapped by bacteria in the activated sludge of bioreactor system. The negative impact of microplastics from wastewater treatment plant was worthy of attention. Moreover, unknown transformation products of microplastics and their corresponding toxicity need in-depth research.

Gathering at the top? Environmental controls of microplastic uptake and biomagnification in freshwater food webs

Microplastics are ubiquitous in the environment, with high concentrations being detected now also in river corridors and sediments globally. Whilst there has been increasing field evidence of microplastics accumulation in the guts and tissues of freshwater and marine aquatic species, the uptake mechanisms of microplastics into freshwater food webs, and the physical and geological controls on pathway-specific exposures to microplastics, are not well understood. This knowledge gap is hampering the assessment of exposure risks, and potential ecotoxicological and public health impacts from microplastics. This review provides a comprehensive synthesis of key research challenges in analysing the environmental fate and transport of microplastics in freshwater ecosystems, including the identification of hydrological, sedimentological and particle property controls on microplastic accumulation in aquatic ecosystems. This mechanistic analysis outlines the dominant pathways for exposure to microplastics in freshwater ecosystems and identifies potentially critical uptake mechanisms and entry pathways for microplastics and associated contaminants into aquatic food webs as well as their risk to accumulate and biomagnify. We identify seven key research challenges that, if overcome, will permit the advancement beyond current conceptual limitations and provide the mechanistic process understanding required to assess microplastic exposure, uptake, hazard, and overall risk to aquatic systems and humans, and provide key insights into the priority impact pathways in freshwater ecosystems to support environmental management decision making.

Semi-automated analysis of microplastics in complex wastewater samples

In order to assess risks to the natural environment from microplastics, it is necessary to have reliable information on all potential inputs and discharges. This relies on stringent quality control measures to ensure accurate reporting. Here we focus on wastewater treatment works (WwTWs) and the complex sample matrices these provide. Composite samples of both influent and effluent were collected over a 24 h period on two separate occasions from eight different WwTWs across the UK. Sludge samples were taken on five occasions from five WwTWs. The WwTW treatments included activated sludge, trickling filter and biological aerated flooded filter with or without tertiary treatment. Using micro-FTIR analysis, microplastics ≥25 μm were identified and quantified. Procedural blanks were used to derive limits of detection (LOD) and limits of quantification (LOQ). Where values were above the LOQ, microplastics in the influent ranged from 955 to 17,214 microplastic particles/L and in the effluent from 2 to 54 microplastic particles/L, giving an average removal rate of 99.8%. Microplastics could be quantified in sludge at concentrations of 301-10,380 microplastics/g dry weight, this analytical method therefore revealing higher concentrations than reported in previous studies. The most common polymers present overall were polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET). We also report on critical considerations for blank corrections and quality control measures to ensure reliable microplastic analysis across different sample types.

Preliminary Screening for Microplastic Concentrations in the Surface Water of the Ob and Tom Rivers in Siberia, Russia

To date, the largest Russian rivers discharging to the Arctic Ocean remain a “blank spot” on the world map of data on the distribution of microplastics in freshwater systems. This study characterizes the abundance and morphology of microplastics in surface water of the Ob River and its large tributary, the Tom River, in western Siberia. The average number of particles for the two rivers ranged from 44.2 to 51.2 items per m3 or from 79.4 to 87.5 μg per m3 in the Tom River and in the Ob River, respectively. Of the recovered microplastics, 93.5% were less than 1 mm in their largest dimension, the largest group (45.5% of total counts) consisted of particles with sizes range 0.30–1.00 mm. Generally, microfragments of irregular shape were the most abundant among the Ob and Tom samples (47.4%) and exceeded microfibers (22.1%), microfilms (20.8%), and microspheres (9.74%) by average counts. Results from this study provide a baseline for understanding the scale of the transport of microplastics by the Ob River system into the Arctic Ocean and add to currently available data on microplastics abundance and diversity in freshwater systems of differing global geographic locations.

Co-occurrence of microplastics and triclosan inhibited nitrification function and enriched antibiotic resistance genes in nitrifying sludge

As more and more microplastics (MPs) and triclosan (TCS), which are added in consumer products, enter wastewater treatment plants with sewage, there are concerns about the impacts of the co-occurrence of MPs and TCS on biological wastewater treatment. In this study, the co-effects of four 1 mg/L MPs (polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC) and polyamide (PA)) and 0.5 mg/L TCS on nitrification were investigated in lab-scale nitrifying sequencing batch reactors (SBRs) (SBR-PE, SBR-PS, SBR-PVC and SBR-PA) relative to control which received no MPs (SBR-CK). The removal rates of NH₄⁺-N and TCS in SBR-CK were around 100% and 92%, respectively. Compared with SBR-CK, no measurable inhibition was observed on nitrification in SBR-PE and SBR-PS, however, SBR-PVC and SBR-PA rapidly lost nitrification function during 14 days, which might be due to the reducing of MLSS caused by PVC, PA and TCS co-loading. Furthermore, PS, PVC and PA decreased the removal of TCS. The co-occurrence of TCS and PS, PVC, PA increased extracellular polymeric substances, reduced microbial diversity and shifted microbial communities. Notably, the acrA-03, mexF, fabI, intI1, intI3 and IS613 genes were enriched by MPs and TCS co-loading. Therefore, the removal of MPs and TCS from wastewater should be prioritized.

Efficiency of Wastewater Treatment Plants (WWTPs) for Microplastic Removal: A Systematic Review

Plastic is widely used for human activities (food packaging, medical, technological devices, etc.) and there is a growing concern regarding the risks for environmental and human health because they have still not been fully evaluated. Particularly, microplastics (primary and secondary) are present in all environmental compartments and this poses a potential threat because of their entry into the food chain. Furthermore, microplastics can absorb numerous pollutants that can be accumulated in the human body through bioaccumulation and biomagnification processes. We carried out a systematic review using a PRISMA approach to verify the efficiency of wastewater treatment plants (WWTPs) for microplastic removal. The international databases (PubMed, Science Direct, Scopus) were used to find published studies on efficiency of wastewater treatment plants (WWTPs) for microplastic removal. The search period was between January 2010 and June 2020. Over 1000 full research papers were initially selected through the use of keywords. After that, the papers were further selected by English language, title, and abstract, and duplicate papers and non-relevant papers were eliminated according to eligibility criteria. Finally, we included 15 full research papers. In each of the 15 full research papers selected, the microplastics identified were categorized by the authors for shape, size, and type of polymers identified. The characterization of the various types of microplastics was performed by Fourier Transform Infrared Spectroscopy (FTIR) or Raman spectroscopy. We have observed how wastewater treatments plants located in different continents (Europe, Asia, North America) mostly use a primary and secondary type of treatment that allows one to reach a high percentage of microplastics removal from wastewater. Most of the wastewater treatments plants investigated reported a microplastics removal efficiency greater than 90%, but despite this, millions of microplastics continue to be released every day into the aquatic environment. Then, in the near future, efficient and common standardized protocols for monitoring MPs should be drawn up, as well as increasing the knowledge of sources and strategies to further reduce microplastics contamination of treated wastewater.

Microplastics in Terrestrial Ecosystems: A Scientometric Analysis

Microplastics, as an emerging contaminant, have been shown to threaten the sustainability of ecosystems, and there is also concern about human exposure, as microplastic particles tend to bioaccumulate and biomagnify through the food chain. While microplastics in marine environments have been extensively studied, research on microplastics in terrestrial ecosystems is just starting to gain momentum. In this paper, we used scientometric analysis to understand the current status of microplastic research in terrestrial systems. The global scientific literature on microplastics in terrestrial ecosystems, based on data from the Web of Science between 1986 and 2020, was explored with the VOSviewer scientometric software. Co-occurrence visualization maps and citation analysis were used to identify the relationship among keywords, authors, organizations, countries, and journals focusing on the issues of terrestrial microplastics. The results show that research on microplastics in terrestrial systems just started in the past few years but is increasing rapidly. Science of the Total Environment ranks first among the journals publishing papers on terrestrial microplastics. In addition, we also highlighted the desire to establish standards/protocols for extracting and quantifying microplastics in soils. Future studies are recommended to fill the knowledge gaps on the abundance, distribution, ecological and economic effects, and toxicity of microplastics.